Astronomy Apply Your Knowledge Discovering Astronomy Chapter 1 page 15 SUMMARY QUESTIONS 1. Briefly describe the appearance of several varieties of galaxies? Spiral galaxies thought to be approximately 100,000 ly in their longest dimension. elliptical galaxies, which are shaped like giant ellipses. irregular galaxies 2. State the hierarchy of objects in the universe, from the smallest to the largest. The Solar System - the major members of the solar system are the Sun & planets (there are other things we'll discuss later - comets, asteroids, etc.). The planets can be further divided into two groups - small, rocky bodies the size of Earth or smaller, and much larger gaseous ones. There is also an interesting distribution of these in space - the small ones are closer to the Sun, and the large ones are further away (except Pluto, which is small and far away). As the semester progresses, we'll see that this arrangement is something we could expect to find in any other planetary systems we may discover later. As we just saw, saying "larger" and "smaller" is not an objective way to describe things. So, we'll look at a few numbers in the table below. 3. Define the astronomical unit (AU) and the light-year (ly) and state their approximate sizes in kilometers. Calculate the size of the light-year in astronomical units? Astronomical Unit (AU) this is the average distance between the Earth and the Sun, or about 150,000,000 km (93,000,000 miles). This is useful when you're talking about distances to things inside the solar system. Light Year (ly) - distance light travels in one year - about 9.5 x 10 15 m or 9.5 x 10 12 km (about 6 trillion miles). Very useful for distances inside our galaxy or distances to nearby galaxies. It's not uncommon, though, to see the size of the universe expressed in light years. Parsec (pc) About 3.26 ly. Distances within the solar system are generally mea- sured by using the average Earth-Sun distance as a stan- dard measuring stick. In familiar units this distance is 93,000,000 miles (or 150,000,000 km1), astronomers generally refer to it simply as one astronomical unit (ab- breviated AU). The average distance of Saturn from the Sun is almost 10 AU. A light-year is the dis- tance that light travels in one year while traveling at the speed of light (300,000 km/sec) APPLYING YOUR KNOWLEDGE 1. Which photograph in this chapter intrigues or interests you most, and why? FIGURE 1-14. The globular cluster M13, a giant aggregate of hundreds of thousands of stars formed early in the history of our galaxy. I now know what a globular cluster looks like lots of white stars and blue haze color between stars. 2. From simply looking at the phtographs in this chapter, can you say which object is the largest? How do you know? FIGURE 1-4 Jupiter. Is one of the largest planets. 3. Why do astronomers use astronomical units rather than miles or kilometers? Questions marked with > require computation. > 4. How many orders of magnitude larger than an atom is a typical person? that they are one to two orders of magnitude. "Giga" and "Mega" are not used as often in science as some of the other prefixes - they pop up more in the computer world, where the numbers they represent are not exactly equal to a billion or a million. Finally, differences between numbers are sometimes classified by "orders of magnitude". This essentially means "powers of 10", so a 600 ft. tall building is two orders of magnitude taller than a person. We can use this idea with weights, times, or whatever. A small car is about one order of magnitude (10 x) heavier than a large person. Generally, this comes up when you are making rough calculations or the things you are comparing are not known to high accuracy. As an example, I could guess that everyone in the class can lift 100 lbs. and be sure that I was within one order of magnitude either way - anyone can lift & 10 lbs., & it's unlikely anyone will be able to lift more than 1,000 lbs. > 5. How many orders of magnitude are there between each of the following pairs: (a) the diameters of the Earth and Sun, (b) the diameter of the Earth and an astro- nomical unit, (c) the length of an astronomical unit and the distance to the nearest star beyond the sun, (d) the distance to the nearest star beyond the Sun and the diameter of the Milky Way galaxy, (e) the diameter of the Milky Way and the distance to the nearest galaxy like ours, and (f) the size of a nucleus and the diameter of the universe? > 6. Use information in Appendix C to determine the number of orders of magnitude between the diameters of Uranus and Neptune, the Moon and Jupiter, Earth and Jupiter, and Pluto and Saturn. Uranus diameter is Neptune diameter is > 7. Write the following numbers in powers of ten notation. (a) 100,000,000 (b) 0,000,000,000,001 (c) 25,000,000,000,000 > 8. Use Appendix C at the back of the book as your source of data for placing the planets into groups having diameters of the same order of magnitude. Repeat for the planetary masses. Inquiry 1-1 Only one of the pairs of numbers below are of the same order of magnitude. Which? (a) 15,000 and 80,000 (b) 500 and 300 (c) 3,000,000 and 4,000 Inquiry 1-2 How many orders of magnitude larger than an average person's height is the Earth's diameter? ANSWERS TO INQUIRIES 1-1. (b) 1-2. Seven orders of magnitude. Seasons The Earth's rotational axis is not perpendicular to its orbital plane. There is an angle between the NCP Earth's axis and the North Ecliptic Pole North end of a line perpendicular to the Earth's orbit & passing through Earth's center of 23.5°. Because we see everything from the same point of view all year if we stay in one place, we see the Sun seem to move not just from East to West daily, also from N to S Summer & Fall and then S to N Winter & Spring. Two times a year, the Earth's axis of rotation does not point towards the Sun at all - it's perpendicular to a line joining the Earth and the Sun. These times are called the Equinoxes (from Latin for equal night - the night & day have equal lengths - 12 h) and they happen on the 1st day of spring about March 21st and the 1st day of fall about September 23rd. On these days, the sun rises exactly in the East & sets exactly in the West. When the northern end of the Earth's axis starts to have a component pointing away from the Sun, we are entering the season of days shorter than 12 hours (Fall). We're in the northern hemisphere, so we see shorter days and less direct sunlight - this is because the Sun is lower in the sky all day long. It also rises more to the south of east and sets more to the south of west. Since the Sun is lower in the sky, less of its light gets spread over more of the Earth, making the rays less intense. A quick example is to shine a flashlight directly down onto a table so that you see a circle of light. Then, tilt the flashlight so the circle gets longer and skinnier. You're not producing any more light, and it's being spread over a larger area, so it gets less intense. These shorter days of less intense sunlight lead naturally to cooler temperatures in our hemisphere. Six months later, the northern tip of Earth's axis starts to point more towards the Sun. The Sun is higher in the sky never overhead outside of the tropics and it rises north of east and sets north of west. Longer days with more direct sunlight heat up our hemisphere & cause summer. There's actually a lag between the longest, most sunlight-intense day (June 21, known as the summer solstice - the Sun is at its northernmost point & turns around & heads south) and the hottest part of the year (usually July/August) which is caused by the oceans serving as a giant heat-sink. They're hard to heat up, & they take a while to cool down (which is why the shortest day with the Sun at the lowest altitude Dec. 21 - winter solstice - Sun's southernmost point, when it is lowest in the sky & turns around heading north is a couple of months before the coldest days usually January/February. Notice that we didn't mention distance to the Sun anywhere in here. We're actually closest to the Sun around the first few days of the year. This acts to make the Northern seasons a little less intense than the Southern ones local climate effects and the distribution of land/sea on the Earth probably make this impossible to detect. Chapter 2 Page 31 Why are these systems of units and ways of writing numbers so important? It's because we have to have a way to describe things objectively in science. We can't communicate effectively with other scientists if we only say things like "this new star is far away from Earth". Not everyone will agree on what "far" means. Even the nearest star (besides the Sun) is very far away if we are considering sending a probe to it. However, if you're talking to someone who studies cosmology (the universe, its beginning, evolution, and end), the nearest star is practically in the same place as the Sun! Using a consistent system of units and giving numbers instead of adjectives prevents misunderstandings. SUMMARY QUESTIONS 1. Distinguish between a theory and a hypothesis. A hypothesis is a reasonable supposition made in describing the results of experiments and observations. It attempts to make predictions of future behavior. Once the evidence for its validity is strong, it becomes a theory. a theory: such validity means that many scientists have repeated and verified confirmed the experi- ments/observations. No theory can be proven to be true. However, data can prove a theory to be false. 2. Distinguish between a fact and an inference. An inference is a conclusion reached by incorporating many lines of reasoning, including observation, experiment, and theory. 3. Describe what scientists mean by a model and its relationship to "truth." A model is a description of a phenomenon, based on observation, experiment, and theory. It is not necessar - ily the truth or reality, a descrition that allows prediction of future behavior. 4. Explain the difference between an observational and an experimental science. List and explain the parti- cular difficulties that face astronomy and describe several advantages that astronomy has over "earth- bound" sciences. Measuring the distances to other planets. Dark Matter 5. Describe why the great distances in astronomy are both a disadvantage and an advantage to the study of astronomy. Angles & Errors Measurement of Angles - The use of an angular measurement is the only way we can say how far apart two objects in the sky appear to be from each other. The big things to remember here are 1) this information alone is not enough to tell us how far apart these two things actually are from each other or from us 2) the angular measurement depends on the true distances between the three objects - for example, from the Earth, the angular separation between the Sun & the full Moon is 180°. If you were on another planet, that separation might be anywhere from 0° to 180° (see below). Small angle approximation- the formula for the angle subtended by something which is far away from you (far meaning a large distance compared to its true diameter) is: The degree is actually a rather large unit of angular measure for most objects in the sky (just like you could measure your height in miles, but it's not very convenient). The degree can be divided into 60 pieces, called minutes of arcor arc-minutes and abbreviated with an apostrophe (35' = 35 minutes of arc). The Moon is about 30' in angular size as seen from Earth. The arc-minute can then be divided into 60 strong>arc-seconds abbreviated with quotation marks. This means that we can write: 1° = 60' = 3,600". Make sure you don't confuse minutes/seconds of time with minutes/seconds of arc, because they measure completely different things (time vs. angle). You've actually encountered this before when you've talked about ounces - an ordinary soft drink can holds 12 ounces (volume measurement) and a pound is 16 ounces (weight measurement). Measurement Errors - Precision & accuracy mean two different things when discussing measurements. If a series of measurements is precise, that means the random error in the measurements is small. The measuring device will repeatedly give the same answers (or nearly the same) when measuring the same things over and over. This does not necessarily mean the answers are correct. A measurement can be very precise and completely wrong. If a series of measurements is accurate, that means that, on average, the measurements are correct. Angles & Errors Measurement of Angles - The use of an angular measurement is the only way we can say how far apart two objects in the sky appear to be from each other. The big things to remember here are 1) this information alone is not enough to tell us how far apart these two things actually are from each other or from us 2) the angular measurement depends on the true distances between the three objects - for example, from the Earth, the angular separation between the Sun & the full Moon is 180°. If you were on another planet, that separation might be anywhere from 0° to 180° (see below). Small angle approximation- the formula for the angle subtended by something which is far away from you (far meaning a large distance compared to its true diameter) is: The degree is actually a rather large unit of angular measure for most objects in the sky (just like you could measure your height in miles, but it's not very convenient). The degree can be divided into 60 pieces, called minutes of arcor arc-minutes and abbreviated with an apostrophe (35' = 35 minutes of arc). The Moon is about 30' in angular size as seen from Earth. The arc-minute can then be divided into 60 strong>arc-seconds abbreviated with quotation marks. This means that we can write: 1° = 60' = 3,600". Make sure you don't confuse minutes/seconds of time with minutes/seconds of arc, because they measure completely different things (time vs. angle). You've actually encountered this before when you've talked about ounces - an ordinary soft drink can holds 12 ounces (volume measurement) and a pound is 16 ounces (weight measurement). Measurement Errors - Precision & accuracy mean two different things when discussing measurements. If a series of measurements is precise, that means the random error in the measurements is small. The measuring device will repeatedly give the same answers (or nearly the same) when measuring the same things over and over. This does not necessarily mean the answers are correct. A measurement can be very precise and completely wrong. If a series of measurements is accurate, that means that, on average, the measurements are correct. It ia difficult to measure great distances since a lot of planets, and stars are so far away. Stars can be very bright and or very dim. Dust particles near the stars may make it more difficult to measure the accurate distance. Stellar Coordinate Systems Because the Earth rotates relative to the distant stars, they are not in the same place every night or even at different times on the same night. There are 2 obvious ways to set your coordinates up - attach them to the Earth, or attach them to the stars. The most convenient way to locate a particular star is probably the altitude-azimuth or horizon system. This specifies a star's location as a number of degrees away from North (measured to the East) which is the azimuth, and a number of degrees above the horizon (measured towards the zenith) which is the altitude (stars below the horizon have negative altitudes). This system is attached to the Earth because if you go outside and find the altitude and azimuth of the top of a tall building, that will not change from day to day or year to year. This is an easy system in one sense, because everyone can find North & make estimates of where "30° altitude" and "105° East of North" would be. Unfortunately, these numbers depend on your location on the Earth (different for NY vs. LA) and the time of year AND time of day. In other words, somebody had to do a significant number of calculations to provide you with the altitude & azimuth of a star in advance from another city. The other system is known as the Equatorial system. This uses coordinates centered on the sky. The two coordinates in this system are known as Right Ascension and Declination. Declination is the star's position N or S of the celestial equator and is measured in degrees. Right ascension is measured from the N-S line which passes through the point where the ecliptic and the celestial equator cross Sun's position on the vernal equinox = 1st day of Spring. RA is therefore like longitude and declination is like latitude. Also, RA is measured in hours (rather than degrees) East from the crossing point mentioned above. The hours represent the fact that the Earth rotates once in 24 hours. One rotation = one complete circle = 360°, so 24h = 360° which means 1 hour of RA = 15°. The good part about these coordinates is that, once you know the RA & dec. for a star, they won't change over your lifetime. The bad part is, you still need to be able to find these stars at night, and RA & dec. are not easily determined by just looking at the night sky. 6. For the hypothetical "expedition to Earth" of this chapter, formulate and evaluate hypothesis that might be made by the alien scientists about life on Earth. Specify the kinds of observations that might be made when attempting to validate the hypothesis. A hypothesis is what an experiment will support or refute. Using a hypothesis to make predictions which are then evaluated by experiments is called deductive reasoning. Starting with experiments and using them to find a hypothesis explaining things is called inductive reasoning. If you observe specific things and then try to generalize them to a hypothesis, that's inductive (you drop 10 different kinds of metal into water, and they all sink - inductively, you conclude that metals are denser than water). Now, someone wants to test your hypothesis that metals are denser than water - they drop lithium into water (it would actually explode, but let's not worry about that). It floats, because it's less dense than water. Your hypothesis now needs to be modified. SOME metals are denser than water. That testing of your hypothesis was deductive. If your hypothesis survives many tests over a period of time (which can include some modifications) it will eventually rise to the level of a theory. For some reason, there is a popular belief that anything which is "only" a theory is somehow untested. The word theory in science actually means a great deal. We talk about the theory of relativity or the theory of quantum mechanics in physics - these are actually the most accurate theories the world has ever known. They make predictions (confirmed by experiment) to accuracies of parts-per-billion or better. As pointed out by Richard Feynman, this is like knowing the distance between New York and Los Angeles to within a few millimeters! Still, we call them theories. Astronomy operates under restrictions which don't constrain the other sciences. Chemists can combine elements to make the compounds they want to study, geologists can collect samples of rocks for study in the lab, biologists can put specimens under a microscope, but astronomers basically have to sit on Earth & collect light (some of which is not in the visible range) to answer their questions. The upside is that, with so much space and so many stars around, almost anything that can physically happen is happening somewhere - you just have to find it. Another thing to keep in mind about astronomy is the connection between distance and time. Light travels at about 300,000 km/sec so whenever you look anywhere, you're really looking into the past. If you're looking across the room, it's only a few nanoseconds into the past, but if you're looking at distant galaxies, you could be looking billions of years into the past. As we just said, we are in one sense restricted by the fact that a human lifetime is so short on the cosmic scale that changes to the stars are not readily apparent. However, we can use the fact that great distances = many years ago to get some sense of stellar or cosmological evolution through time. We can't see what our galaxy was like 5 billion years ago, but if we're looking at light that left other galaxies 5 billion years ago, that could give us some important clues. The observations may include observations of how life is like on earth from what we do each day. From human life to plant life, and other life. 7. Explain how the position of the alien scientists is similar to that of present-day astronomers (and also how it is different). They maybe observing us or other things in the same similar ways we are observing things with telescopes. 8. Compare and contrast the characteristics of pseudoscience presented in the chapter with those of science. Science and Pseudo-Science Science makes predictions based on observations, interpretation of data, and logical reasoning. Science should be completely unbiased - a scientist will generally try to think of every possible way to knock down his/her own work, for the simple reason that others will certainly do it. If you can think of some reason why what you have suggested is wrong, you also know more about what the right answer might be. Pseudoscience generally starts from the end and works backward to find facts which seem to match the desired endpoint. Difficulties of Astronomy - Time scale of modern astronomy (~100 years) is virtually nothing on the scale of stellar/galactic/cosmological change. What could you learn about a human's life cycle by watching a snapshot of thousands of humans? You'd have to guess which of these different images represent steps on a timeline, and which don't. Baby boys don't grow into middle-aged women on the way to being old men. Also, size plays a role, but it's not absolute - babies grow into larger people, but people in their nineties are not generally the largest people around, and NFL linebackers are not the oldest people on Earth. Philosophies of Science - Modern science is based on the testing and formation of hypotheses. These are basically ideas that make testable predictions and explain pre-existing observations. Growth of Science in the 20th century- Science has seen tremendous growth in the last 100 years. Newton's ideas, which most of science rests on, have been shown to be incomplete (NOT the same thing as being wrong - they are still good enough for many purposes. Only when we talk about speeds which are close to the speed of light or distances which are smaller than an atom or incredible concentrations of mass do we start to notice significant deviations from the laws we've used for 350 years.) There are many different reasons for the increase in knowledge lately. First, society can afford the "luxury" of having a larger percentage of the population involved in science. We don't need to have 50% of the country farming to feed themselves and the other 50%. Second, governments and societies have seen great benefits come from scientific studies, and that encourages investment in science. Technology, which can be thought of as the movement of an idea or device from the laboratory to mass production, has made similar leaps since about 1900. At that time, cars were rare, planes didn't exist, and electricity was somewhat new. Since then, science has helped refine cars & planes, designed rockets, created lasers, transistors, computers, etc. There has been a beneficial feedback from technology into science - the presence of computers allows scientists to gather far more data, analyze it more exhaustively, and test theories faster than would ever be possible without them. Pseudoscience can generally be distinguished from true science by determining whether the ideas espoused can ever be at risk, whether they are open to modifica- tion and evolution into new ideas, whether they claim to supply simple answers to complex questions, whether practitioners play the role of an underdog, and whether they do much research and publish it where trained scientists can examine the purported results. The term for those who claim to be doing science, when in fact, they are not playing by the rules of science is pseudoscientist, and what pseudoscientists pro- duce is called pseudoscience. The prefix pseudo liter- ally means that which deceptively resembles or appears to be something else. Separating Science and Pseudoscience there are lots of tools you can use to do this. First, skepticism is important. If you hear an extraordinary claim (this magnet will relieve pain anywhere in your body caused by anything), that should set off alarm bells for you. Examine things like 1) is there some way this could possibly work? This requires knowing some of the basic principles of science that we'll hopefully learn in here. For example, getting more energy out of something than you put in (perpetual motion) seems to crop up now and then. Most scientists won't even bother trying to deflate these claims anymore - they're too ridiculous to waste time on. The Patent Office will reject any application like this without reading further. It's kind of like someone telling the same knock-knock joke over & over again - you'll quickly stop saying "Who's there?" because you know how it will turn out & you're tired of it. 2) where did you hear about this magical device/theory? Has it been published in a reputable scientific journal? Or was it published at the writer's expense? The reason science operates by publishing in journals is that articles submitted are sent to two or more reviewers - other scientists who are experts in the subject of the article. Their job is to carefully analyze the experiment or theory discussed and look for any holes the author might have missed. If a mistake makes it past the reviewers and editors, it will be published for hundreds or thousands (depending on the journal) of other experts in that general area of study to see. This process has a tendency to quickly kill bad ideas. As a general rule, scientists who announce discoveries via news conferences rather than journal articles are looked at suspiciously by others scientists. 3) How does the author present the work? Frequently, pseudoscientists will claim that "organized science" is somehow out to get them. There is some conspiracy between the government, big businesses, and/or scientists to keep news of their discovery quiet. 4) Have other people been able to confirm or reproduce the results? If not, that should be a clue that something is off. 5) Are testable predictions made by the theory? The theory should be more than a "fit" to selected pieces of data (or even all of the available data) - something new should come out of the theory. 6) Existing data shouldn't be ignored - in some cases, it will be mentioned and then brushed off for some less-than-valid reason. Going back to an earlier example, Einstein's theory of relativity did NOT change the validity of Newton's laws in most cases (almost all cases confined to the Earth). In fact, if you look at certain limits (small masses, low velocities), you'll find Einstein's laws produce Newton's laws. These points will help you decide the value of a new theory or new product. Even with the number of governmental agencies regulating food, medicines, vitamins, etc., there's a huge amount of garbage which dishonest people will try to sell to anyone who doesn't know better. This brings up the question of motivations for pseudoscience, and there are many of these: First, there are people who are genuinely convinced that they have made a fundamental breakthrough and it is being ignored or suppressed for some reason (generally referred to as crackpots). Frequently, the reason given for this obstruction is that "these scientists don't want to admit that everything they know is wrong and that they have to go back to square one to understand my theory". Possible? Sure. There will be people in any field who resist change just because it is a change. What history has shown, though, is that when someone presents a "crazy" idea which actually holds up to scrutiny, the scientists who learn it and accept it first are generally the ones who are able to publish lots of important papers on the further implications of the new idea. It has happened with both quantum theory and relativity in the 20th century. Another motivation is profit - the person presenting the new theory is selling something based on it, and they have a financial interest in convincing others that they're right. Sales of wearable magnets, copper bracelets, etc., are an example of this. The government is as susceptible to pseudoscience as any person. NASA has, in the past, funded truly ridiculous ideas. This is sometimes defended by using arguments like "Well, you always need to question everything." The problem with this idea is that, once an idea has been questioned over and over and over again, and never failed even once, you reach a point where you're wasting your time and money by investigating further. How many glasses do you need to drop before you accept the fact that gravity makes things fall toward the Earth? 9. Explain how theory and observation interact in the development of scientific ideas. theory is guessing on things that are not yet verified. observation is seeing or looking at images or reading information on scientific ideas. one example of theory would be the Describe the theory of the Moon's origin currently fa- vored by many astronomers. Today, many astronomers favor a scenario often called the impact theory, which postulates a glancing collision between a large, Mars-sized object and a youthful, molten Earth. Computer simulations of such a catastrophic event show that most of the bits and pieces of splattered Earth could have coalesced into a stable orbit, forming the Moon. APPLYING YOUR KNOWLEDGE 1. State and analyze some of the conclusions an alien scientist might make about people on Earth through an analysis of their eating habits. Eating with good manners and with not good manners. Eating with forks, spoons, and or with hands. 2. About which of the following sources of informa- tion might you tend to be more skeptical on ques- tions of science? (a) Time or Newsweek magazine; (b) The National Inquirer; (c) Scientific American; (d) The New York Times. (b) The National Inquirer 3. Which of the following publishing houses might you expect to be the least reliable on questions of science? (a) Random House Inc. (b) Bantam Press (c) Creation- Life Publishers (d) Oxford University Press. (b) Bantam House 4. Which of the following true statements are facts, and which are inferred results? (a) The average density of material in the Earth's core is 11 times that of water. (b) Jupiter's average diameter is 11 times that of Earth. (c) All stars like the Sun get their energy from conver- sion of hydrogen to helium. b is a fact c is inferred 5. Critically analyze the following statement: "The first generation of human beings ever to have grown up educated about the true nature of the universe is still alive." No they are not alive since the first generation of human beings was a long time ago. 6. Discuss why science is not degraded when talking about it in terms of the "game of science," as done in the chapter. The Game of Science Science may be thought of as an intellectual game in the sense that it has certain rules that need to be followed. Activities in science. Chapter 3 Page 44 SUMMARY QUESTIONS 1. What do scientists mean by random and systematic errors? Give an example of each. This means that the systematic error is small. Systematic errors are always in one direction - random errors can be high or low. An example of random error would be stepping on a scale 10 times and getting 4 or 5 different answers. An example of systematic error would be if a friend is standing behind you & keeps putting his foot on the scale when you get on. oe example of the problems caused by systematic errors in astronomy is found in the 1922 estimate of the size of the universe made by astronomer Jacobus Kapteyn. He didn't use the assumption that all stars have the same intrinsic brightness and that apparent variations in brightness are only due to different distances to the stars. His estimate of the universe's diameter was 10,000 l.y. This was later shown to be too small by a factor of ~10 6. The problem was that absorption of light by interstellar dust wasn't considered to be too severe from results of preliminary surveys. The star counts were all interpreted incorrectly in a systematic way rather than a random way. Systematic errors are always in one direction - random errors can be high or low. An example of random error would be stepping on a scale 10 times and getting 4 or 5 different answers. An example of systematic error would be if a friend is standing behind you & keeps putting his foot on the scale when you get on. 2. Explain how systematic errors affected Kapteyn's estimates of the size of the universe. One example of the problems caused by systematic errors in astronomy is found in the 1922 estimate of the size of the universe made by astronomer Jacobus Kapteyn. He didn't use the assumption that all stars have the same intrinsic brightness and that apparent variations in brightness are only due to different distances to the stars. His estimate of the universe's diameter was 10,000 l.y. This was later shown to be too small by a factor of ~10 6. The problem was that absorption of light by interstellar dust wasn't considered to be too severe from results of preliminary surveys. The star counts were all interpreted incorrectly in a systematic way rather than a random way. APPLYING YOUR KNOWLEDGE 1. Discuss the errors involved in comparing your car's odometer readings against the one-mile markers on a highwa.y. Assume the comparison continues for 20 miles. (Please do not do this while you are driving!) 2. Suppose you made a number of precise inaccurate angular measurements with either your fist, a protrac- tor or a cross-staff. What might you do to improve the accuracy? Improve the alignment of the protractor or a cross-staff when making measurements. 3. Think about and discuss the possible errors present the last time you made a measurement of any type. (Such a measurement might include weighing yourself, measuring an ingredient when cooking, filling you car with fuel, etc.) If using a electronic scale a battery might run low on power or not standing correctly on a scale might give in accurate readings. Their may had been a little more baking soda in a tablespoon. >4. Suppose the dark rifts in the Milky Way were long skinny tunnels without stars. Assume a typical tunnel has a 10 ly diameter, and that a typical star moves with a speed of 10 km/sec. How long should it take for stars to fill the tunnel? (Remember, the distance something moves is given by its speed times the length of time it travels.) 10 x 10 00 10 =100 >5. What would be the apparent size of a quarter if it were at a distance of 3000 miles (i.e., across the length of the United States)? (Such an angular size could easily be seen by a modern radio telescope.) The Moon is about 30' in angular size as seen from Earth. The arc-minute can then be divided into 60 strong>arc-seconds abbreviated with quotation marks. This means that we can write: 1° = 60' = 3,600". Make sure you don't confuse minutes/seconds of time with minutes/seconds of arc, because they measure completely different things (time vs. angle). >6. What would be the width of the so-called "canals" on Mars if they were to have an angular size of 0.25 seconds of arc when Mars is at its closest approach to the Earth (roughly 50 million miles)? 0.25 50 >7. What would be the angular size of the Earth for an observer on the Moon? x multiply distance from Earth to the Moon. 60' or 90' angular size The Moon is about 30' in angular size as seen from Earth. The arc-minute can then be divided into 60 strong arc-seconds abbreviated with quotation marks. This means that we can write: 1° = 60' = 3,600". >8. If the Sun were at the distance of the nearest star- 4.3 ly - what would its angular size be? Convert your answer (which the formula gives as a decimal fraction of a degree) into a decimal fraction of a second of arc. ANSWERS TO INQUIRIES 3-1. Yes. All the measurements are ratios, so if the proportion is the same, so is the result. 3-2. 0.53degrees; 0.53 X 60 = 31.8'; 31.8 X 60 = 1908" 3-3. The average value is 12 ft 8.4 in. 3-4. 4 yards X 36 in/yard = 144 in. 4 m X 39.37 in/m = 157 in. 3-5. (a) random and systematic; (b) random; (c) random. You always have random errors. In this example, random errors are less than systematic errors. Chapter 4 Page 67 SUMMARY QUESTIONS 1. What observations did ancient people use to indi- cate that the Earth was round? How did these observations interact with the culture's theoretical and philosophical underpinnings? Early observations People have studied the motions of the Sun, planets, and stars through the sky for thousands of years. In all parts of the world, astronomers realized that the patterns are predictable. The Mayans, Egyptians, Chinese, and Arabs all made important contributions centuries before western science began. Early astronomers predicted eclipses and observed "guest stars" (exploding stars in our galaxy), developed calendars, understood solstices/equinoxes, and noticed that the planets were definitely different from the stars. By observing the shadow of the Earth on the Moon during lunar eclipses, the Greeks knew the Earth must be a sphere at least as early as about 500 BC. They also correctly determined the sizes of the Earth and Moon. Early astronomers predicted eclipses and observed "guest stars" (exploding stars in our galaxy), developed calendars, understood solstices/equinoxes, and noticed that the planets were definitely different from the stars. By observing the shadow of the Earth on the Moon during lunar eclipses, the Greeks knew the Earth must be a sphere at least as early as about 500 BC. They also correctly determined the sizes of the Earth and Moon. 2. What are the principal motions of the Earth? Explain the effects that each of these motions has on the apparent motions of the stars and other objects in the sky. The Moon moves around the Earth the same direction in which the Earth moves around the Sun. Since the Earth is moving around the Sun while the Moon tries to circle the Earth, we have two distinct "months", just like we have two kinds of days - solar and sidereal. The Moon's sidereal period is 27.3 days. This is the amount of time necessary for the Moon to make one trip around the Earth relative to the stars. The time for the Moon to go from one phase through its full cycle and back to that phase is longer, just as the time between two passages of the Sun through the local meridian is longer than that for two passages of a star through the local meridian. This longer period is called the Moon's synodic period because it is relative to the Sun. The length of the synodic period is easily found from the sidereal period. 360° are covered in 27.3 days, which means the Moon moves 13.2° around the Earth each day. However, after 27.3 days, the Earth has moved (360°/365.25)*27.3 = 26.9° from where it was when the Moon started its orbit. 26.9°/(13.2° per day) = ~ 2 days. 27.3 + about 2 = 29.5 days for the synodic period. (it takes about one more step to see that because of the constant chase between the Earth and Moon. While the Earth moved almost 27° during the Moon's sidereal period and the Moon has to move for 2 more days to get near it, the Earth is still running from the Moon for those 2 days and the Moon will have to move a few hours to finally catch it. When these are all added to the 27.3, you get about 29.5)

Phases of the Moon - The phase of the Moon (as seen by people on Earth - there's no such thing as an "absolute" phase) depends on the positions of the Moon, Sun, and Earth. Half of the Moon is always lit by the Sun (except in the rare case of a lunar eclipse when part or all of the Moon enters Earth's shadow). During a full Moon, the lit half points directly at the Earth. During a New Moon, it points directly away from the Earth (we see only the dark side, so we can't see anything). Incidentally, there is no dark side of the Moon - ½ of it is always dark and ½ of it is always lit (except for lunar eclipses) and the halves change slowly and constantly over the Moon's orbit. An astronaut landing anywhere on the Moon would see the Sun crawl across the sky, taking about 2 weeks to move from horizon to horizon, and then would have 2 weeks of night waiting for the next sunrise. However, since the Moon always keeps the same face pointed at the Earth, wherever the Earth was in the sky when the astronaut landed, it would always stay there unless he/she moved.

The basic phases of the Moon are New (Moon between Earth & Sun), 1st quarter (Moon directly "behind" the Earth relative to the direction Earth is going in its orbit), Full Moon (Earth between Moon & Sun), and 3rd quarter (Moon "in the way" of Earth's movement through its orbit). Additionally, there are crescent phases (between New and 1st or 3rd quarter - only a sliver of Moon visible) and gibbous phases (between Full and 1st or 3rd quarter - all but a little of the Moon visible), each of which can be waxing heading towards Full or waning heading towards new. Moon's orbit and eclipses The Moon's orbit is not exactly in line with the Earth's orbit =apparent path of the Sun through the sky = ecliptic. If the two orbits were in the same plane, we'd have a solar eclipse and a lunar eclipse every month. As it is, we have them much less often - 2 to 5 times per year, each. The line marking the intersection between Earth's orbit and the Moon's orbit does not point in a constant direction. If it did, there would be two times each year the same time every year when eclipses might occur. This would be when the line of intersection called the line of nodes pointed at the Sun. When the Moon passes through the ecliptic plane, it has to be either the New Moon or the Full Moon before an eclipse can happen. Things could only line up this way when the line of nodes points to the Sun. Adding to the complexity of predicting eclipses, the Moon's orbital plane and therefore its line of nodes does not stay in the same place. It precesses (backwards relative to Earth's motion) at a rate of one revolution every 18.6 years. This is caused by the fact that the Earth's rotational axis is not only precessing, but wobbling slightly changing the 23.5° angle by a few arc seconds over 18.6 years. Motion of the stars - the stars move constantly on different cycles & timescales. The daily rotation of the Earth makes stars (and Sun, Moon, and planets) appear to move from East to West across the sky. The projections of the Earth's geographic North & South poles onto the sky are known as the North & South Celestial Poles (NCP & SCP). These are the points in the sky that the stars seem to rotate around. We only see the NCP - the SCP is below the horizon for us, and can only be seen from the equator or below, just like the NCP can only be seen from the equator or above. The projection of Earth's equator onto the sky is known as the celestial equator. There happens to be a bright star very close (currently) to the NCP - it's known as the North Star because it always lies in the North (unless it's directly overhead, which means you're already at the North Pole). As you move from the North Pole down to the Equator, Polaris moves from overhead down to the horizon. Its altitude (number of degrees above the horizon) is equal to your latitude. Motion of Sun - The stars seem to rise a few minutes earlier every day. This is b/c the Sun seems to move to the East relative to the stars. To observe the relative Sun/stars motion, we need to define two kinds of day. The solar day is the standard one we use every day - it's the time between two successive observations of the Sun going overhead (or through the local meridian, which is the line overhead connecting the NCP and the SCP). This is 24 hours. The other kind of day is the sidereal day. This is the time between successive observations of the same star going overhead. This is also the time it takes the Earth to rotate 360°. This is 23h 56m. The reason for the difference in times is that, over a day, the Earth moves around the Sun by about 1° (1° because it takes 365 days to move the full 360° around the Sun ~ 1°/day). The Earth now has to rotate through 361° rather than 360° to put the Sun back in the same place. How long does this extra degree take to rotate through? It is easily calculated as: 360° in 23h 56m (or 1436 minutes). 1436 minutes/360° = 3.99 minutes (~ 4 minutes) per degree. Therefore, it takes 23h 56m + 4m = 24 hours to get the solar day. This also means that the length of the year in days depends on which kind of day you're using - it's 365.25 solar days, but 366.25 sidereal days. The other way to understand this is to realize that the trip around the Sun gives one more rotation as seen by the stars. That's where all the other numbers really come from. Also, this has nothing to do with leap years - the leap year exists because the Earth doesn't make a whole number of rotations during one trip around the Sun. There's no reason it should - the two rotational motions are not strongly connected. the stars move constantly on different cycles & timescales. The daily rotation of the Earth makes stars and Sun, Moon, and planets appear to move from East to West across the sky. The projections of the Earth's geographic North & South poles onto the sky are known as the North & South Celestial Poles (NCP & SCP). These are the points in the sky that the stars seem to rotate around. We only see the NCP - the SCP is below the horizon for us, and can only be seen from the equator or below, just like the NCP can only be seen from the equator or above. 3. What effect does an observer's latitude have on what he or she will see in the sky? Depends on where you are on Earth you may see different objects in the sky from different angles. Your latitude can be determined by observing the angle between your northern horizon and the North Celestial Pole. Since Polaris, the North Star, is within 1° of the North Celestial Pole, Polaris can be used as a fairly accurate marker of the North Celestial Pole. Determining latitudes in the southern hemisphere is more difficult because there is no bright star within a few degrees of the South Celestial Pole. Circumpolar constellations are those constellations close enough to a celestial pole so that they never pass below an observer ’s horizon, but instead pass directly between the observer’s celestial pole and northern or southern horizon at their lowest points in the sky. At different latitudes the celestial pole will be at different distance above an observer’s horizon. If the observer is at a latitude of 60° N, then all constellations within 60° of the North celestial pole will be circumpolar. However, if an observer is at a latitude of only 30° N, then only those constellations within 30° of the North Celestial Pole will be circumpolar. Determining latitudes in the southern hemisphere is more difficult because there is no bright star within a few degrees of the South Celestial Pole. 4. Explain why the solar day is longer than the sidereal day. The solar day is the standard one we use every day - it's the time between two successive observations of the Sun going overhead (or through the local meridian, which is the line overhead connecting the NCP and the SCP). This is 24 hours. The other kind of day is the sidereal day. This is the time between successive observations of the same star going overhead. This is also the time it takes the Earth to rotate 360°. This is 23h 56m. The reason for the difference in times is that, over a day, the Earth moves around the Sun by about 1° (1° because it takes 365 days to move the full 360° around the Sun ~ 1°/day). The Earth now has to rotate through 361° rather than 360° to put the Sun back in the same place. How long does this extra degree take to rotate through? It is easily calculated as: 360° in 23 hours 56 minutes (or 1436 minutes). 1436 minutes/360° = 3.99 minutes (~ 4 minutes) per degree. Therefore, it takes 23h 56 m + 4 m = 24 hours to get the solar day. This also means that the length of the year in days depends on which kind of day you're using - it's 365.25 solar days, but 366.25 sidereal days. The other way to understand this is to realize that the trip around the Sun gives one more rotation as seen by the stars. That's where all the other numbers really come from. Also, this has nothing to do with leap years - the leap year exists because the Earth doesn't make a whole number of rotations during one trip around the Sun. There's no reason it should - the two rotational motions are not strongly connected. Seasons The Earth's rotational axis is not perpendicular to its orbital plane. There is an angle between the NCP (Earth's axis) and the North Ecliptic Pole (North end of a line perpendicular to the Earth's orbit & passing through Earth's center) of 23.5°. Because we see everything from the same point of view all year (if we stay in one place), we see the Sun seem to move not just from East to West daily, but also from N to S (Summer & Fall) and then S to N (Winter & Spring). Two times a year, the Earth's axis of rotation does not point towards the Sun at all - it's perpendicular to a line joining the Earth and the Sun. solar day The period of time between the instant when the Sun is directly overhead (i.e. at noon) to the next time it is directly overhead. sidereal day The time needed for a star on the celestial sphere to make one complete rotation in the sky. 5. What is precession? What is its effect on the positions of stars? Precession - Something that will change a star's RA & dec. (VERY SLOWLY) is the phenomena of precession. This is the gradual change of the direction in which the North pole is pointing. The NCP therefore moves around the sky over time. It actually traces out a circle every 26,000 years. This is what we meant by saying Polaris was the current North Star, not a permanent one. In about 12,000 years, Vega will be the star closest to the NCP. In 26,000 years, it'll be Polaris again. This precession is just like the way a spinning top moves. It not only spins very quickly on its axis, but its axis moves around in a smaller circle so that the top seems to trace out a cone. This is because the axis is spinning in the gravitational field of the Earth, and the Earth is pulling down on the top of the top. The net result is precession. The same thing happens when the Earth spins rapidly (on a scale of 26,000 years, a day is very quick!) in the gravitational fields of the Sun and Moon. precession The slow change in the direction of the axis of a spinning object, caused by some external influence. 6. How can you determine your latitude from the observed altitude of Polaris? Your latitude can be determined by observing the angle between your northern horizon and the North Celestial Pole. Since Polaris, the North Star, is within 1° of the North Celestial Pole, Polaris can be used as a fairly accurate marker of the North Celestial Pole. Determining latitudes in the southern hemisphere is more difficult because there is no bright star within a few degrees of the South Celestial Pole. 7. What do we mean by the terms celestial sphere, celestial equator, ecliptic, meridian, declination, and right ascension? celestial sphere Imaginary sphere surrounding the Earth, to which all objects in the sky were once considered to be attached. celestial equator The projection of the Earth's equator onto the celestial sphere. ecliptic The apparent path of the Sun, relative to the stars on the celestial sphere, over the course of a year. The stars seem to rise a few minutes earlier every day. This is b/c the Sun seems to move to the East relative to the stars. To observe the relative Sun/stars motion, we need to define two kinds of day. The solar day is the standard one we use every day - it's the time between two successive observations of the Sun going overhead (or through the local meridian, which is the line overhead connecting the NCP and the SCP). This is 24 hours. The other kind of day is the sidereal day. declination Celestial coordinate used to measure latitude above or below the celestial equator on the celestial sphere. right ascension Celestial coordinate used to measure longitude on the celestial sphere. The zero point is the position of the Sun on the vernal equinox. 8. What two factors result in seasonal variations on Earth? How do they operate to create differences between summer and winter in the Northern Hemisphere? When the Earth is farther away from the sun in December it becomes colder, and is winter. Is tilted away from the sun. When the Earth is closer to the sun in June it becomes warmer, and is summer. Is tilted toward the sun. 9. How do the different phases of the Moon come about? Your answer should include drawings. The motions of the moon, and the sun. An eclipse is possible when the Full or New Moon passes near a node the line of nodes is pointing near the Sun. For about 15-19 days on either side of perfect alignment line of nodes pointing at the Sun, an eclipse can happen if the Moon is in the right place. This time is called an eclipse season. Because of the Moon's regression of nodes mentioned before, this happens a little more often than 2 times a year. It's 2 times in about 346 days. Since a year is longer than this, by a little, we could conceivably have 3 eclipse seasons in one year. This happens about every 9 years or so. We'll always have at least 2 eclipse seasons in a year, though, so that's why we say there is a minimum number of eclipses (of all kinds). Because the eclipse season is a little longer than the cycle of phases (29.5 days) we could also have 3 eclipses within about 30 days. In other words, we could have a solar eclipse at New Moon, a lunar eclipse at the following Full Moon, and another solar eclipse at the next New Moon. This happens about once every 7 years or so. Very rarely, these special circumstances coincide and we get 3 eclipse seasons in one year, with one of them being a 3-eclipse season. That gives two 2-eclipse seasons and one 3-eclipse season for a total of 7 eclipses of all kinds. This is the absolute maximum for a year.

(The material in the next five paragraphs is very detailed - you may just want to skim it)

Eclipses occur in predictable cycles. To go from one eclipse to the exact same "kind" of eclipse, we have to wait for 3 different cycles to coincide. The first cycle is the Moon's cycle of phases, or synodic month (29.53 days). We know this is important because Solar eclipses (for example) only happen when the Moon is new. The next cycle is the time between passages of the Moon through a node (actually, the same node. The nodes are different - one is called the ascending node because the Moon is coming from below the Ecliptic plane to above it as it crosses the node. The other is the descending node). This period is known as the draconic month and is 27.21 days. We know this is important because, if the Moon is not at or near a node when it's Full or New, there will be no eclipse because the shadow of the Moon (or Earth) will not fall on the Earth (or Moon).

Finally, will the Moon be close to the Earth (total solar eclipse) or far from the Earth (annular eclipse)? It seems like this would just depend on the draconic month above, but the Moon's orbit is also sliding around while it precesses, kind of like a bent hula-hoop. The period of this last effect is called the anomalistic month, and is 27.55 days long.

These three periods are all nearly the same length, which means it will take a long time for them to all get back to the start of their cycles again. As an example, imagine you're watching a race where one runner is slightly faster than a second, and the second is slightly faster than a third. They're all together at the start, but they move away from each other as the race continues. If it goes on for a very long time, the fastest runner will pass the slowest runner, and then later pass the second fastest runner. As you can imagine, it will take many laps before they all end up at the same place again (by which time the fastest runner will have made several more trips around the track than the slowest).

In our case, 223 Synodic months = 6585.32 days, 242 Draconic months = 6585.36 days, and 239 anomalistic months = 6585.54 days. That's close enough. This time period is known as a Saros cycle or just a Saros. It's about 18 years, 10 1/3 days (or 11 1/3, depending on leap years in the 18 years). When you observe one eclipse, you can know that if you wait for one Saros cycle, you should see another one. However, since the number of days is not a whole number, the eclipse will not be at the same place on Earth. It's about 1/3 of a day more than a whole number, so the second eclipse will happen about 1/3 of the way around from the first one. The eclipse of Aug.11 1999 (totality over Europe) and the one of Aug. 21 2017 (totality here) are the same in terms of the Saros. 3 Saros cycles will return an eclipse to approximately where it was on the Earth. That means the eclipse of July 20, 1963 took a path near the one which will be taken by the 2017 eclipse over the US.

It's important to mention that this does not mean that you have to wait 54 years between eclipses at the same place. It just tells you when you're essentially guaranteed another one based on your last one. At any given time, there are many different Saros cycles in progress, so you can potentially see multiple eclipses in just one year. The essentially guaranteed above means that this doesn't go on forever. After hundreds of years, the fact that our 3 cycles above are all slightly different (by fractions of a day) and all are different from a whole number of days finally adds up, and that particular Saros is over. End of very detailed stuff There are a few kinds of solar eclipses - the most dramatic is the total solar eclipse where the full face of the Sun is covered & the corona (outer atmosphere of the Sun) is visible. North or South of the path of totality, observers will see a partial solar eclipse which can be anything from just less than totality (near the path) to just a small segment of the Sun disappearing briefly (far away from the path of totality). Also, since the Moon's distance to the Earth is not constant, its angular size is not constant - if the eclipse happens when the Moon is farther away from the Earth, its size will appear smaller and a ring of sunlight will remain. This is called an annular eclipse. Places experiencing a total solar eclipse will have the Moon's umbra darkest central part of the shadow pass over them. Partial solar eclipses are seen when the penumbra (outer partial shadow) passes over a place. An annular eclipse is seen if the umbra is too short to reach the Earth's surface. 10. What causes solar eclipses? Lunar eclipses? At what phase of the Moon does each occur? waning crescent waxing crescent Eclipses & the Motion of the Moon Moon - Annular Eclipse Total/Partial Eclipse Time - Risings and Settings - As the Earth turns, everything in the sky (except some satellites) will rise in the East and set in the West because the Earth is turning from West to East. Sunrise occurs when the part of the globe 90° to your east is pointed directly at the Sun, and sunset occurs when the part of Earth 90° to your west is pointed at the Sun, as shown below. The Moon, stars, and planets all rise & set based on the same ideas shown above. When the Earth rotates around so that your Eastern horizon swings past them, they appear to rise, climb through the sky, and then set as your Western horizon swings away from them. For example, in the picture below (taken from the North Pole) Charleston is represented by a red dot. The horizon is 90° away from Charleston in every direction. We can get a good approximation of Charleston's horizon by pretending we are where the blue dot is (it's easier to draw the horizon from there). In the top picture, the double-headed arrow represents the Eastern and Western horizons. As you can see, the arrow on the California side of the globe points to the West (where California is) and the arrow on the Atlantic Ocean side of the globe points to the East (where the Atlantic is from here). 12 hours later, the Earth has rotated around so that our horizons have switched around. In the top picture, the Moon was on Charleston's Eastern horizon (so it was rising) and the Sun was on the Western horizon (so it was setting). After 12 hours, the bottom picture shows that the Sun is now rising (because it's on the Eastern horizon) while the Moon sets in the West. Always remember: there is no rising and setting. It all boils down to the Earth turning and your horizon moving down to uncover some celestial object, and moving up on the other side of the sky to cover something else. 11. What are the observed apparent motions of the planets with respect to the background stars? Describe them. Stellar Coordinate Systems Because the Earth rotates relative to the distant stars, they are not in the same place every night or even at different times on the same night. There are 2 obvious ways to set your coordinates up - attach them to the Earth, or attach them to the stars. The most convenient way to locate a particular star is probably the altitude-azimuth or horizon system. This specifies a star's location as a number of degrees away from North (measured to the East) which is the azimuth, and a number of degrees above the horizon (measured towards the zenith) which is the altitude (stars below the horizon have negative altitudes). This system is attached to the Earth because if you go outside and find the altitude and azimuth of the top of a tall building, that will not change from day to day or year to year. Parallax measurements are limited because we measure the apparent motion of a star due to the motion of Earth around the Sun. Earth's orbit is so small compared to the distances to stars that even the nearest stars show barely measurable apparent motions. Therefore, we are limited to only the nearest stars. If Earth's orbit were larger, we could measure the parallax of stars at greater distances. its color to change from blue (4000 A) to red (7000 A) APPLYING YOUR KNOWLEDGE 1. Is the model of the Earth suggested by Anaximander any better in explaining observations than the Baby- lonian model? In particular, compare the observations of the sky that could be predicted using the Babylon- ian model with those that could be predicted using the Greek model. 2. What effects would precession have on the seasons? Precession - Something that will change a star's RA & dec. (VERY SLOWLY) is the phenomena of precession. This is the gradual change of the direction in which the North pole is pointing. The NCP therefore moves around the sky over time. It actually traces out a circle every 26,000 years. precession The slow change in the direction of the axis of a spinning object, caused by some external influence. 3. What would the Earth's phase be for an observer on the Moon if the lunar phase for an observer on Earth is waxing crescent? waning moons waning crescent the moon is in the waning crescent - it's visible now only an hour or two before sunrise. On Monday, April 23, the moon will be "new" at 11:26 a.m. EDT. At this time, the moon is in conjunction with the Sun - it's roughly between the Earth and the Sun. If it were perfectly aligned with the Earth and Sun, a solar eclipse would be visible somewhere on Earth. 4. Where in the sky would you look at midnight to see Jupiter when it is at quadrature? southern sky On the night of June 17-18, the planet Jupiter reaches west quadrature. This means that the Earth, Sun and Jupiter are at a 90-degree angle. At this time, the Earth is moving nearly 17 miles every second closer to the gas giant. As a result, Jupiter is rapidly growing in apparent size. For example, on this date the planet has a diameter of 40.3 seconds of arc. One month later it has increased to 44.4 seconds of arc and it has brightened 0.2 magnitudes. At this time through a telescope, Jupiter looks almost gibbous since the shadow of the planet is noticeable along its western limb. Around quadrature, Jupiter's shadow (as seen from the Earth) extends more sideways. Consequently, its outer Galilean moons, Ganymede and Callisto can briefly be seen after they emerge from the shadow of the planet and before they pass behind it. Jupiter rises about 1 a.m. and before dawn it is high in the southern sky, well suited for observation. North Jupiter is passing through eastern quadrature (on the 17th), so the distances between each moon and the shadow it casts will be at a maximum. When jupiter is at quadrature, the angle ? takes on its maximum value, and sin ? max = 1AU D J . At quadrature, the Sun-Earth-Jupiter angle is 90 In sequence, the Moon's phases are, beginning with new: a) waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent 5. If the star Vega rises tonight at 8:A.M., at what time should you be looking for it to rise three months from now? Explain. 6. If the Sun rises at 6:A.M., at what approximate time does the waxing gibbous Moon set? The moon is in the sky for roughly 12 hours in a 24-hour period. Therefore, if the full moon rises at 6 PM, it will set at 6 AM. 7. Use tracing paper to trace stars from the maps in Appendix G; then try making your own constellations. Are the traditional constellations any better or more useful than yours? >8. What is the maximum possible lunar altitude for an observer at the North Pole? Hint: A drawing will be helpful. >9. Use a drawing to help you explain which conditions produce the most favorable total solar eclipse: Earth nearest or farthest from the Sun, and Moon nearest or farthest from the Earth. >10. At what latitude is an observer for whom the stars within 25 degrees of the pole are circumpolar? >11. Refer to Figure 4-12b and determine the latitude at which the photograph was taken. >12. How many degrees into the southern celestial hemisphere can an observer at a latitude of 40 degrees north see? >13. For what southern latitudes will the Sun never be observed at the zenith? ANSWERS TO INQUIRIES 4-1. Flat Earth: same constellations are observed from all locations; height of the Sun above the horizon at noon is constant throughout the year; shadow on Moon during lunar eclipses is a straight line. Round-Earth; change in constellations as observer moves north or south; height of the Sun above the horizon might vary throughout the year; shadow on Moon during lunar eclipses always part of a circle. 4-2. It would produce a straight-line shadow on the Moon. 4-3. Observational: Disappearance of boats, different stars seen at different points on Earth, and the shape of the Earth's shadow on the Moon. Theoretical: Solves problem of "which way is down" and fits in with notion that the sphere is the most perfect shape. 4-4. On the horizon. 4-5. Stars must move parallel to the celestial equator. 4-6. It would be the apparent path of the Earth around the celestial sphere. it would be the plane defined by the Earth's orbit. 4-7. 10:00 P.M. 4-8. The Sun is 23.5 degrees from directly overhead south of the celestial equator, moving low across the southern sky during the day. Most of the diurnal motion of the Sun is below the horizon, giving the shortest number of daylight hours of any day of the year. 4-9. At the equator the altitude of the Sun at noon varies by only 23 1/2 degree throughout the year; for this reason seasonal variations are small. At a pole, however the variations are extreme because for six months of the year the Sun never gets above the horizon. 4-10. The Moon moves eastward at about 13degrees per 24 hours, or about 0.5 degrees per hour. This equals the Moon's diameter every hour. 4-11. 6:P.M. 4-12. New Moon 4-13. Full Moon. 4-14. The Sun is in Capricornus (Cap); Mercury is between Capricornus (Cap) and Sagittarius (Sgr); Venus is between Ophiuchus (Oph) and Scorpius (Sco). 4-15. Venus would show a quarter phase; Jupiter, gibbous. 4-16. The sidereal period is difficult to observe because the positions of both the planet and Earth change, making it difficult to know when the planet has completed one full cycle. Because the time of opposition is easy to define by an observation, the time interval between two oppositions is easy to get. 4-17. Cassiopeia and the bowl of the Dipper will both be at about 30 degrees altitude, on either side of the pole star. 4-18. May. 4-19. April, May. 4-20. East, overhead. 4-21. Castor and Pollux. 4-22. In the southeast, about 50 degrees up from the horizon. Chapter 5 Page 92 SUMMARY QUESTIONS 1. What is the significance of the observations of Aristarchus, Eratosthenes, and Hipparchus? What are the principles used to make their measurements of the sizes of the Earth and Moon? Aristarchus (300 BC) determined that the distance from Earth to the Sun must be many times greater than the Earth-Moon distance due to the fact that the 1st and 3rd quarter phases of the Moon are equally spaced in its cycle of phases. In other words, we will see the these two phases of the Moon only when the Earth-Moon line and the Moon-Sun line make a 90° angle. If the Sun was close to the Earth, the time between 3 rd & 1 st quarters would be less than half of the cycle as shown below. On the right, the Sun is very far away compared to the Moon and the red lines are very close to parallel. Aristarchus was also able to estimate the relative sizes of the Earth and Moon by precisely timing lunar eclipses. The time from the first appearance of the Earth's shadow on the Moon until the Moon was completely in the shadow was proportional to the Moon's size. The duration of totality of the lunar eclipse (time for which the Moon is completely within Earth's shadow) was proportional to the Earth's diameter. Finally, using the existence of eclipses he determined that the ratio of the Moon's diameter to its distance was the same as the ratio of the Sun's diameter to its distance. By using something like the small angle approximation, he was able to guess at the Sun's size. This estimate depends on accurately knowing the distance to the Sun, though, and since Aristarchus thought the Sun was only 1/10 as far away as it is, his estimate of its size was 1/10 of what it is. In about 200 BC, Eratosthenes measured the Earth's size in traditional units for the first time. He did this by using the fact that the Sun was known to shine directly down a well in Syene (near the modern-day Aswan dam) on one day of the year (if this only happened once a year, what's the latitude of Syene if we know that it is somewhere in the Northern hemisphere?). On that same day, he measured the angle of the Sun in his hometown of Alexandria. He got an angle of 7°, and he knew that the distance between the two towns was 5000 stadia (1 stadium - probably about 0.1 miles). This was enough to give him the circumference of the Earth in stadia. magnitude scale A system of ranking stars by apparent brightness, developed by the Greek astronomer Hipparchus. Hipparchus was the first to record the phenomenon of precession and accurately find its period of 26,000 years. He was able to do this because he had made high-precision observations of many stars and compared the changes in his coordinates and those of Babylonian astronomers. He also developed the magnitude system. 2. What are two methods by which the order of the planets from the Sun could be determined? 3. What planetary observations must a reasonable model of the solar system incorporate? In your answer use diagrams to show how the Ptolemaic and heliocentric hypotheses explain the observations. The Ptolemaic model explained retrograde motion using a complicated system of wheels within wheels. Each planet moved in a small circle called an epicycle, and the center of the epicycle moved along a larger circle around Earth called a deferent. Earth was placed slightly off center of the deferent. As the planet is carried by both the deferent and the epicycle, it will appear to go through retrograde motion when the planet is on the inside half of its motion of the epicycle. heliocentric model A mode of the solar system which is centered on the Sun, with the Earth in motion about the Sun. The heliocentric (Sun-centered) model. Copernicus asserted that Earth spins on it axis, and like all other planets, orbits the Sun. This model explains the observed daily and seasonal changes in the heavens, as we have seen, but it also naturally accounts for planetary retrograde motion and brightness variations. The critical realization that Earth is not at the center of the universe is now known as the Copernican revolution. 4. What is meant by stellar parallax? Explain its cause. How can parallax be used to distinguish between heliocentric and geocentric hypotheses? Why did the Greeks not observe stellar parallax? The distances to the nearest stars can be measured using parallax-the apparent shift of an object relative to some distant background as the observer's point of view changes. The parallax is determined by comparing photographs made from the two ends of the baseline. 5. What role did the concept of uniform circular motion play in the history of astronomical thought? Give examples from several eras. The philosopher Plato taught that heavens were perfect and unchangeable. To Plato, the most perfect geometrical figure was the sphere and the natural motion of a sphere is rotation about an axis. Additionally, perfect motion was uniform, that is, at constant speed. Therefore, all heavenly bodies being perfect must be composed of perfect geometrical figures (spheres) moving in perfect motion (uniform circular motion). The Ptolemaic model explained retrograde motion using a complicated system of wheels within wheels. Each planet moved in a small circle called an epicycle, and the center of the epicycle moved along a larger circle around Earth called a deferent. Earth was placed slightly off center of the deferent. As the planet is carried by both the deferent and the epicycle, it will appear to go through retrograde motion when the planet is on the inside half of its motion of the epicycle. (See the Concept Art).

  • Both the Ptolemaic and Copernican system assumed uniform circular motion and needed to employ equants and epicycles. Ptolemy’s system required them to account for the variation in the orbital speed of a given planet and retrograde motion. Copernicus’ system required them to account only for the variation in the orbital speed of the planets. Both also assumed a celestial sphere at a great distance. 6. What were specific astronomical contributions made by Copernicus and Brahe? What was the importance of these contributions? The Heliocentric model did rectify some small discrepancies and inconsistencies in the Ptolemaic System, but for Copernicus, the primary attraction of heliocentricity was its simplicity, its being " more pleasing to the mind." To this day, scientists still are guided by simplicity, symmetry, and beauty in modeling all aspects of the universe. By relegating Earth to a non-central and undistinguished place within the solar system. Retrograde Motion. The Copernican model of the solar system explains both the varying brightnesses of the planets and the phenomenon of retrograde motion, The heliocentric (Sun-centered) model. Copernicus asserted that Earth spins on it axis, and like all other planets, orbits the Sun. This model explains the observed daily and seasonal changes in the heavens, as we have seen, but it also naturally accounts for planetary retrograde motion and brightness variations. The critical realization that Earth is not at the center of the universe is now known as the Copernican revolution. 4. What was the Copernican Revolution? The Copernican Revolution was The Birth of Modern Science. 7. State and explain Kepler's three laws. Explain Kepler's second law in terms of the conservation of angular momentum. Kepler's first law has to do with the shapes of the planetary orbits: The orbital paths of the planets are elliptical (not circular), with the Sun at one focus. Kepler's second law addresses the speed at which a planet traverses different parts of its orbit Kepler's second law a line joining the planet to the sun sweeps out equal areas in equal intervals of time. The three shaded areas A, B, and C are equal. Any object traveling along the elliptinal path would take the same amount of time to cover the distance indicated by the three red arrows. Therefore, planets move fast when closer to the Sun. Kepler's third law states that The square of a planet's orbital period is proportional to the cube of its semi-major axis. 8. What are the principal astronomical discoveries of Galileo? Explain how these discoveries may have accelerated the acceptance of the heliocentric hypothesis. Galileo claimed that Earth orbits the Sun. Galileo also saw four small points of light, invisible to the naked eye, orbiting the planet Jupiter, and the four small points of light were 4 moons. Galileo builr a telescope for himself in 1609 and aimed it at the sky. Using his telescope, Galileo discovered tha the Moon had mountains, valleys, and creates-terrain in many ways reminiscent of that of Earth. He found that the Sun had imperfections-dark blemishes now known as sunsports. By noting the changing appearance of these sunspots from day to day, he inferred that the Sun rotates, approximately once per month, around an axis roughly perpendicular to the ecliptic plane. 9. State Newton's laws of motion and the law of gravity. Explain how, in principle, they can be used to explain the orbiting of one body about another. Newton's laws of motion and his law of universal gravitation provided a theoretical explanation for Kepler's empirical laws of planetary motion. Just as Kepler modified the Copernican model by introducing ellipses in place of circles, so too did Newton make corrections to Kepler's first and third laws. Because the Sun and a planet feel equal and opposite gravitational forces (by Newton's third law), the Sun must also move (by Newton's first law), due to the planet's gravitational pull. 10. What are some specific astronomical examples of how Newton's laws have been shown to be valid descrip- tions of nature? Yet another of Newton's laws. Newton postulated that the reason the Moon follows us around the Sun (for example) is that the Moon and the Earth attract each other through a force called gravity. He believed that the strength of this force depended on the mass of each body involved as well as the separation of the bodies. 11. How were the heliocentric hypothesis and the Earth's rotation finally confirmed observationally? How did Newton's laws play a role in demonstrating the Earth's rotation and revolution? Evidence for Spinning Earth One obvious demonstration of Earth's rotation can be made by imagining a pendulum basically a rock on a string swinging at the North Pole. Assume it's swinging back and forth in the same plane as the 90° W longitude line and the 90° E longitude line. As time passes, the Earth will rotate under the pendulum, but the pendulum will keep swinging in the same plane. This can also be demonstrated at other latitudes, but it's simplest at the poles. APPLYING YOUR KNOWLEDGE 1. Make up a table that lists, chronologically, the contributions to astronomy made by Aristarchus, Apollonius, Eratosthenes, Hipparchus, Ptolemy, and Pythagoras. Include dates. Aristarchus (300 BC) determined that the distance from Earth to the Sun must be many times greater than the Earth-Moon distance due to the fact that the 1st and 3rd quarter phases of the Moon are equally spaced in its cycle of phases. In other words, we will see the these two phases of the Moon only when the Earth-Moon line and the Moon-Sun line make a 90° angle. If the Sun was close to the Earth, the time between 3rd 1st quarters would be less than half of the cycle as shown below. On the right, the Sun is very far away compared to the Moon and the red lines are very close to parallel. On the left, where the Sun is much closer, you can see that when the Sun and Earth are 90° apart as seen from the Moon, the Moon and Sun are NOT 90° apart as seen from the Earth. This shows that the time from 1st to 3rd quarter would be longer than the time from 3rd back to 1st. Aristarchus was also able to estimate the relative sizes of the Earth and Moon by precisely timing lunar eclipses. The time from the first appearance of the Earth's shadow on the Moon until the Moon was completely in the shadow was proportional to the Moon's size. The duration of totality of the lunar eclipse (time for which the Moon is completely within Earth's shadow) was proportional to the Earth's diameter. Finally, using the existence of eclipses he determined that the ratio of the Moon's diameter to its distance was the same as the ratio of the Sun's diameter to its distance. By using something like the small angle approximation, he was able to guess at the Sun's size. This estimate depends on accurately knowing the distance to the Sun, though, and since Aristarchus thought the Sun was only 1/10 as far away as it is, his estimate of its size was 1/10 of what it is. Also, all of these sizes/distances were measured in units of Earth diameters. No one knew the Earth's true diameter, so the knowledge about the Sun & Moon was incomplete. Eratosthenes - In about 200 BC, Eratosthenes measured the Earth's size in traditional units for the first time. He did this by using the fact that the Sun was known to shine directly down a well in Syene (near the modern-day Aswan dam) on one day of the year (if this only happened once a year, what's the latitude of Syene if we know that it is somewhere in the Northern hemisphere?). On that same day, he measured the angle of the Sun in his hometown of Alexandria. He got an angle of 7°, and he knew that the distance between the two towns was 5000 stadia (1 stadium - probably about 0.1 miles). This was enough to give him the circumference of the Earth in stadia. Hipparchus was the first to record the phenomenon of precession and accurately find its period of 26,000 years. He was able to do this because he had made high-precision observations of many stars and compared the changes in his coordinates and those of Babylonian astronomers. He also developed the magnitude system. 2. If you had been a traditional scholar in the mid-1500s, what arguments would you have presented against the Copernican system? Copernicus In the early to mid 1500's, Copernicus, who was familiar with Aristarchus' idea of a Sun-centered universe, began to try to fit the heliocentric model to the observed behavior of the sky. The heliocentric universe explained many observations more simply than the geocentric model. The planets could now be put in order by distance from the Sun, and that information both explained planetary regression and provided a constant increase in sidereal period with distance. The problem with the Copernican theory was inability to abandon the idea that planets could move in anything other than perfect circles. This idea had persisted since Ptolemy, and by keeping it, Copernicus had to add epicycles and deferents to his model to explain existing planetary observations. The new model needed even more epicycles than the Ptolemaic model. The general principle in science (called Occam's razor) is that the simplest explanation that fits the facts is the correct one. More epicycles made this theory more complicated. By relegating Earth to a non-central and undistinguished place within the solar system. Retrograde Motion. The Copernican model of the solar system explains both the varying brightnesses of the planets and the phenomenon of retrograde motion, The heliocentric (Sun-centered) model. Copernicus asserted that Earth spins on it axis, and like all other planets, orbits the Sun. This model explains the observed daily and seasonal changes in the heavens, as we have seen, but it also naturally accounts for planetary retrograde motion and brightness variations. The critical realization that Earth is not at the center of the universe is now known as the Copernican revolution. The Copernican Revolution was The Birth of Modern Science. 3. Of the following people, who in your opinion made the most important contribution to astronomy: Copernicus, Brahe, Kepler, Galileo, Newton? Explain. Galileo. Galileo also saw four small points of light orbiting the planet Jupiter, and the four small points of light were 4 moons. Galileo built a telescope for himself in 1609 and aimed it at the sky. Using his telescope, Galileo discovered that the Moon had mountains, valleys, and creates-terrain in many ways reminiscent of that of Earth. He found that the Sun had imperfections-dark blemishes now known as sunsports. By noting the changing appearance of these sunspots from day to day, he inferred that the Sun rotates, approximately once per month, around an axis roughly perpendicular to the ecliptic plane. Kepler's first law has to do with the shapes of the planetary orbits: The orbital paths of the planets are elliptical (not circular), with the Sun at one focus. Kepler's second law addresses the speed at which a planet traverses different parts of its orbit Kepler's second law a line joining the planet to the sun sweeps out equal areas in equal intervals of time. The three shaded areas A, B, and C are equal. Any object traveling along the elliptinal path would take the same amount of time to cover the distance indicated by the three red arrows. Therefore, planets move fast when closer to the Sun. Kepler's third law states that The square of a planet's orbital period is proportional to the cube of its semi-major axis. Chapter 6 Page 116 SUMMARY QUESTIONS 1. What are the names of the planets in order of their distance from the Sun? Earth Venus is 3rd planet from the sun. Mars Jupiter Saturn Uranus Mercury Neptune Pluto 2. What are the two major groups of planets? List the characteristics that distinguish members of each group? The jovian planets are giant outer planets farther away from the sun. Jupiter, Neptune, and Saturn and have ring systems. The terrestrial planets are small inner planets closer to the sun. Earth, and Mars, and Venus. Have no ring systems. 3. What are the major regularities in the orbits and motions of the planets that need to be explained by any successful theory of the origin of the solar system? What exceptions are there to these regularities? The Solar System There are a number of regularities among the planets of the Solar System. If we closely examine the similarities and differences in the planets and their orbits, we should be able to learn enough to make an intelligent guess about the formation of the Solar System. Among the easier things to notice are 1) the planetary orbits are ellipses, but the eccentricities are very low - even Pluto's orbit is very hard to distinguish (visually) from a circle 2) the orbits are also in nearly the same plane as Earth's orbit (the ecliptic). Again, the most extreme violation of this is Pluto, and its orbit is still only at a 17° angle to Earth's. 3) the planets all move around the Sun in the same direction (counterclockwise as seen from far above Earth's North Pole). Additionally, most of the planets spin in the same direction they orbit. We can also say that the planetary axes are roughly perpendicular to the planetary orbits (again, this is an approximation - the angle is 23.5° for us, and about the same for Mars) for most of the planets 4) Most planetary satellites move around their primary (the planet they orbit) in the same direction (CCW) and generally in the plane of the ecliptic 5) the planets are roughly ordered by size and composition (if we ignore Pluto - we'll talk about why that's a good idea later) - close to the Sun, we have small, rocky planets while far from the Sun we have very large, gaseous planets. 4. What observational evidence can you use to criticize the early nebular and collisional hypotheses of the origin of the solar system? Ideas about Solar System formation A simple idea that could explain the angular momentum problem would be if we said the cloud was rotating only slowly, it collapsed to form the Sun, and the Sun later captured the speedy (therefore high angular-momentum) planets later as it traveled the galaxy. The biggest problem here is that while this would explain the A.M. problem, we then have to explain why all the planetary orbits are in approximately the same plane, why they all move CCW around the Sun, why they are split into two groups of very similar members, etc. There are too many coincidences to explain for this to be a believable theory. The Nebular hypothesis (a simple version of it) instead says that the cloud condensed with some rotational motion, which tended to flatten the cloud into a disk-like shape (this is what would happen physically, so this is a good sign). During the collapse, rings of material might be left behind at larger distances from the center. Particles in these rings would attract each other & gradually assemble into planets (which would all be moving in the same direction - another good sign). Problems with this idea include: 1) it's not easy to get hot gases to collect anywhere - they have a tendency to spread out rather than contract (hot air balloons work because the air inside spreads out & takes up more space). 2) If the future Sun was spinning so fast that rings of material were being thrown off of it rather than continuing inward with the rest of the Sun, the Sun should still have a much greater percentage of the angular momentum of the Solar System than what we observe 3) This still doesn't explain small rocky planets near the Sun and large, gaseous planets far away from it. 5. What are some possible reasons for the dramatic differences in composition between the terrestrial and Jovian planets? Jupiter is hit with more astroids and or dust particles due to it's larger size. The terrestrial planets are smaller than the jovian planets, and the terrestrial planets have no rings. The jovian planets are larger than the terrestrial planets, and the jovian planets have rings. Jupiter and Saturn have rings. Collision (or Catastrophic) hypothesis This one says that a passing star managed to pull some material out of the Sun as the two got near one another. This might explain the common direction of the planets' orbits around the Sun, but there is no explanation for why the material from the Sun would condense into planets, why there are differences in composition between the large & small planets, or even the A.M. problem. 6. Why were dust grains important to the formation of the solar system? What role might turbulence have played in its formation? Dust Grains - Dust particles seem to have played a major role in the ability of clumps to form in the early gas cloud. The dust particles (solids that are around 10 -5 - 10 -6 cm in size) would have been composed of things like Carbon and Silicon and their compounds. The reason is that, while hydrogen and helium made up 98% or so of the mass of the Solar System (and still do), they would not have contributed much to the dust grains. Helium will not combine with other elements (except under extreme conditions which didn't exist in the early cloud) and it will not even condense to form a solid except near absolute zero while under high pressure (also not likely in the early Solar System). Hydrogen is also very volatile (fast moving & therefore not likely to condense) by itself, but it combines readily with other elements. It may have been present in solid ices of water, methane, and ammonia. The dust particles are more likely to stick to each other during collisions, and therefore form larger bodies. Also, the amount of dust increased as the cloud collapsed, radiated heat, and then cooled. As these elements condensed, they would do so around other dust particles like frost on outdoor objects. This would add to the size of the dust particles. Dust Grains Dust particles seem to have played a major role in the ability of clumps to form in the early gas cloud. The dust particles (solids that are around 10 -5 - 10 -6 cm in size) would have been composed of things like Carbon and Silicon and their compounds. The reason is that, while hydrogen and helium made up 98% or so of the mass of the Solar System (and still do), they would not have contributed much to the dust grains. dust grains in the solar nebula formed condensation nuclei around which matter began to accumulate. This vital step greatly hastened the critical process of forming the first small clumps of matter. Once these clumps form, they grew rapidly by sticking to other clumps. condensation nuclei Dust grains in the interstellar medium which act as seeds around which other material can coagulate. The presence of dust was very important in causing matter to clump during the formation of the solar system. 7. Where is most of the angular momentum in the solar system located? Why was the distribution of angular momentum a problem for earlier hypotheses of solar system formation? Describe a process thought to solve the angular momentum problem. Angular Momentum Problem (A.M. Problem) Any theory explaining the formation of the Solar System will have to explain the fact that, while the Sun has 99.8% of the Solar System's mass, it has only about 2% of the angular momentum (in addition to explaining the facts mentioned in the previous section). The Sun has angular momentum because it is rotating on its axis. That's just another kind of motion in a circle. The Earth also has some angular momentum due to its spin, but compared to its orbital angular momentum (which exists because it moves around the Sun), it's very small. One of the earliest and most enduring ideas about the formation process includes a collapsing cloud of gas and dust which eventually formed the Solar System. If this cloud had any rotational motion at all (and it would take a strange arrangement of objects for it to not have at least some rotational motion), by the law of conservation of angular momentum, that should not change when the cloud collapses to form the Sun. As the radius of the cloud would have been much larger than that of the Sun, we would expect the Sun's rotational speed to be very much larger than the cloud's would have been. This assumption stems from the fact that we can look at the cloud as a collection of individual particles - each one has some angular momentum relative to the center of the cloud. Since most of the particles ended up in the Sun, it's logical to think most of the angular momentum should end up there as well. We need to think about why it didn't. Angular momentum depends on the mass, radius, and rotation rate of an object. It's done by using the fact that the planet and the Sun are essentially an isolated system. The planet moves in a circle (ellipse, really) around the Sun and therefore has angular momentum relative to the Sun. By the law of conservation of angular momentum, if the planet gets closer to the Sun (r decreases), it must speed up (v increases). That's why the planet sweeps out equal areas in equal times. Angular Momentum Problem (A.M. Problem) Any theory explaining the formation of the Solar System will have to explain the fact that, while the Sun has 99.8% of the Solar System's mass, it has only about 2% of the angular momentum (in addition to explaining the facts mentioned in the previous section). The Sun has angular momentum because it is rotating on its axis. That's just another kind of motion in a circle. The Earth also has some angular momentum due to its spin, but compared to its orbital angular momentum (which exists because it moves around the Sun), it's very small. One of the earliest and most enduring ideas about the formation process includes a collapsing cloud of gas and dust which eventually formed the Solar System. If this cloud had any rotational motion at all (and it would take a strange arrangement of objects for it to not have at least some rotational motion), by the law of conservation of angular momentum, that should not change when the cloud collapses to form the Sun. 8. How have astronomers attempted to detect planets orbiting other stars? There are a couple of possible ways to detect planets based on this idea. One way would be to measure the change in the star's position through time as a result of this wobble. This method requires incredibly precise position data, though, because the stars are very far away and in the case of the Earth & Sun, the wobble is only a few hundred km per year. No planets have been detected this way yet. Another possibility is to measure the Doppler shift in the star's light as it moves back and forth around the ellipse. The Doppler shift of sound is familiar to anyone who has noticed the change in pitch of a siren as it approaches you & then passes you & moves away. The sound is shifted to a higher frequency when it's moving towards you and a lower frequency moving away. The amount of the shift depends on the velocity of the source relative to the speed of sound (interstate speed is about 10% of the speed of sound, or Mach 0.1). The same effect occurs with light. A green light (center of the visible spectrum) would seem more bluish (blue = higher frequency than green) when moving towards you, and more reddish (red = lower frequency than green) when moving away. APPLYING YOUR KNOWLEDGE 1. Hypothesis: The solar system formed when a passing star pulled material from the Sun that then formed the planets. Present evidence both for and against this hypothesis, and state your final conclusion. Modern Theories of Formation Current ideas about the Solar System's formation are based on a modified nebular hypothesis which still has the system forming from a condensing cloud, but adds features to help the model match reality. The cloud of gas and dust will begin to collapse under its own gravity, but it doesn't happen instantly. The particles in the dust cloud (both gas and dust) have potential energy. 2. List all observations about the solar system that are exceptions to the generally observed features. Remember that we already know the ratio of the radii (it's about 11). This means the ratio of volumes is about 11 3 or 1331 (we're doing rough calculations here - we didn't start with EXACTLY 11 so we can't really quote our final result to 50 decimal places. We'll call it 1300). So, we get that Jupiter has 1300 x the volume of Earth.

    There's only one thing stopping us from saying that Jupiter has 1300x the mass of Earth - Jupiter is mostly light gas and Earth is mostly rock. Because of that, Jupiter is really only about 315 times the mass of Earth. For comparison, all the other planets in the Solar System combined have a smaller mass than Jupiter. Because Jupiter is the largest of the gaseous planets, they're sometimes called the Jovian planets (this was the Roman adjective for things relating to Jupiter). The others are Saturn, Uranus, and Neptune, in that order from the Sun. These worlds are different from the inner ones in several ways - they all have ring systems (only Saturn's are obvious, but the others are there), they all have multiple satellites (8 or more), they are all far from the Sun (compared to the Earth), they have very heavy atmospheres, and they're cold. As we study these planets in more depth, we'll see that many of these things are related and therefore not too surprising (lots of satellites could reasonably be associated with ring systems, large distances from the Sun coincide with thick, cold atmospheres, etc.). A large part of the course will be separating things that really are unexpected with things that are only odd until we learn how they really work.

    The inner planets also have many similarities - they're mostly rocky, warm, and covered with thin atmospheres, if any (these properties aren't as uniform as they are for the Jovian planets - Venus actually has a very thick atmosphere compared to the Earth, it's still thin on the scale of the planet's size, unlike the Jovian planets). 3. Explain why the following two definitions of volatile materials are the same. (a) Volatile materials are those that condense at low temperatures. (b) Volatile materi- als are those that turn to vapor at low temperatures. 4. Use the condensation sequence of Figures 6-13 and 6-14 to explain in your own words the reasons different planets differ in chemical composition. condensation theory Currently favored model of solar system formation which combines features of the old nebular theory with new information about interstellar dust grains, which acted as condensation nuclei. 5. Refer to Figure 6-5b, which shows the inclinations of the planets to their orbital planes. For each planet, discuss what you expect for seasonal variations throughout the planet's year. >6. What fraction of planetary orbital angular momentum is held by Jupiter? Saturn? (We are neglecting rota- tional angular momentum, which is less than that from the orbital motion.) >7. Compute Pluto's density if its mass is 0.0024 the mass of the Earth and its diameter 2302 km. Express the density relative to the density of the Earth. What conclusions about the nature of Pluto might you draw from the observed density? 0.0024 +2302 = 0.2326 >8. What would be the angular separation between the Sun and Jupiter if they were observed from the distance of Alpha and Proxima Centauri, the nearest stars, at a distance of 4.3 light years? Compute the distance a dime would have to be for its angular size to match the angle you computed. Chapter 7 Page 139 SUMMARY QUESTIONS 1. What is the icy conglomerate model of a comet? What evidence is there for it? How can it explain the various phenomena observed in comets? comet A small body, composed mainly of ice and dust, in an elliptical orbit about the Sun. As it comes close to the Sun, some of its material is vaporized to form a gaseous head and extended tail. 2. Why does the tail of a comet always point away from the Sun? Why may a comet have more than one tail? Comets remain one of the areas where amateur astronomers have a reasonable chance of discovery when competing with professional astronomers. Until a comet is noticed, its orbit and existence are unknown. They are found by carefully examining photographs (digital or film) of the same part of the sky over time. Anything that moves relative to the star field (and isn't a planet or other known object) must be a comet or asteroid. Comet structure- Comets appear to be made of gas and dust and are generally thought of as dirty snowballs. The parts of the comet are 1) nucleus - the icy core - usually about 10 km or so across 2) Coma - bright head of gases boiling off of the comet as the comet is heated by the Sun 3) Ion tail - ionized matter from the comet which trails behind it and always points away from the Sun 4) Dust tail - made of small dust particles which scatter & reflect sunlight - these particles orbit the Sun just as the comet does, and therefore follow a curved path. Charged particles streaming from the Sun (called the solar wind) tends to push the ion tail directly away from the Sun. The radiation pressure of the Sun's light tends to push both tails away from the Sun. Through spectroscopic analysis of the tails and evidence from the International Comet Explorer spacecraft, it has been determined that comets are mostly ices of water, methane and ammonia (combinations of the most abundant element in the universe, H, with the most abundant reactive elements (C, N, and O). As the comet gets closer to the Sun, even less volatile elements are boiled off of it (Sodium, Calcium, Silicon, Iron). This may explain the fact that comets sometimes show strange & unpredictable behavior in their orbits. If there is ice under some kind of less volatile crust, the crust could allow the comet to heat as it approaches the Sun. Eventually, the ice (and now gas) under the crust can break through a weak spot and act like a jet, altering the comet's orbit.

    Comet orbits and origins - Cometary orbits are usually very much unlike planetary orbits. They can have any inclination relative to the ecliptic, they orbit in very eccentric ellipses, and they orbit in either direction without preference. Comets like these are members of the Solar System, just as the planets are - elliptical orbits repeat periodically, which is why we have the notion of period of an orbit. Comets can also have hyperbolic orbits as well. When Newton's laws are used to derive Kepler's 1st law, these orbits also appear as solutions. The big difference is that they represent the orbits of high-velocity objects and they are not closed (in other words, a comet in a hyperbolic orbit does not come back - it comes in once & escapes forever). These wild comets were probably not thrown out of another planetary system and into ours - it's more likely that they were ordinary comets who had a too-close encounter with a large object somewhere in the Solar System (probably Jupiter) and had their orbit permanently altered.

    Comets seem to come from two regions near the Solar System - one is known as the Oort cloud, named after a Dutch astronomer who predicted the existence of a large spherical cloud 50,000 - 100,000 AU's from the Sun and surrounding it. There may be trillions of comets in this cloud. This cloud would have a dramatically larger size than the planetary part of the Solar System, but it would still fall under the gravitational influence of the Sun. This cloud is only inferred from other evidence so far - it has not been observed tiny objects the size of comets and 100,000 times farther from the Sun than Earth may be impossible to see for quite some time. Rather than condensing where they are now where the density of objects must have been very low, current theory suggests that these comets were formed in the area of the outer planets but were then caught in gravitational interactions with them & thrown out of the inner Solar System, forming the cloud. Passing stars may disturb this cloud enough to send showers of comets towards the Sun - this kind of mechanism has been suggested as a cause of mass extinctions on the Earth in the past. Another source of comets which has been observed is known as the Kuiper belt. This disk-shaped region is from 30-50 AU's from the Sun (in the area of Neptune & Pluto) and would provide short-period comets (<200 years) closer to the ecliptic plane. Objects in this belt seem to be like comets in some respects (like size and composition). At least 70 objects have been observed in this belt, although there may be tens of thousands which are larger than 100 km. Neptune's orbit seems to provide the inner boundary to this belt, and some scientists think that, due to similarities in the compositions of one of Neptune's moons and Pluto, both of these objects originally formed in the Kuiper belt. Cometary observations from spacecraft- Several countries sent spacecraft to Halley's comet during its last approach in 1986. Halley's comet was found to be one of the least-reflective objects in the solar system, reflecting less than 5% of the Sun's light (Earth reflects about 39% of the sunlight that hits it - Venus about 59%, Mars about 15%). The jets mentioned above were also found on Halley and it was discovered to be over 300K. Its density was so low that the comet must be mostly empty space. More spacecraft are planned for the future to determine the composition more accurately as well as investigate the structure of comets (rocky, dustball, or what). As it comes close to the Sun, some of its material is vaporized to form a gaseous head and extended tail. 3. What evidence do astronomers have in favor of Oort's hypothesis of a comet cloud beyond the orbit of Pluto? Oort Cloud Spherical halo of material surrounding the solar system, out to a distance of about 50,000 A.U., where most comets originate. These wild comets were probably not thrown out of another planetary system and into ours - it's more likely that they were ordinary comets who had a too-close encounter with a large object somewhere in the Solar System (probably Jupiter) and had their orbit permanently altered. Comets seem to come from two regions near the Solar System - one is known as the Oort cloud, named after a Dutch astronomer who predicted the existence of a large spherical cloud 50,000 - 100,000 AU's from the Sun and surrounding it. There may be trillions of comets in this cloud. This cloud would have a dramatically larger size than the planetary part of the Solar System, but it would still fall under the gravitational influence of the Sun. This cloud is only inferred from other evidence so far - it has not been observed (tiny objects the size of comets and 100,000 times farther from the Sun than Earth may be impossible to see for quite some time). Rather than condensing where they are now (where the density of objects must have been very low), current theory suggests that these comets were formed in the area of the outer planets but were then caught in gravitational interactions with them & thrown out of the inner Solar System, forming the cloud. Passing stars may disturb this cloud enough to send showers of comets towards the Sun - this kind of mechanism has been suggested as a cause of mass extinctions on the Earth in the past. Pluto's is noticeably elliptical. Its orbit is also the one that is at the most dramatic angle to the Earth's orbital plane. Finally, it's much smaller than even Mercury - about ½ its radius and less than 10% of its mass. The current theory to explain these disagreements is that Pluto didn't form the way the rest of the planets did and is more likely a captured traveler from the outskirts of the Solar System. If it didn't form in the same area, it's not such a big surprise that it doesn't fit in with the other planets. Using Newton's laws of motion, he discovered that the comet had an orbital semi-major axis of about 18 AU's (it gets as far away as 35 AU's from the Sun - what does this say about the eccentricity of its orbit compared to the orbits of the planets?). This comet was traced back in time & has been observed (although not recognized as the same comet at the time) for over 2,000 years. Comets have been observed and recognized as different from the stars and planets for thousands of years, but it was not until Edmund Halley successfully predicted the return of a comet that real understanding of them began. Halley had noticed that comets were observed in 1531, 1607 and 1682. He believed that these three comets were actually just different appearances of one comet with a 76 year period. He predicted it would return in 1758, which it did (although he was already dead). 4. What do we mean by the term "minor planet?" What are they? Where are they found? How can they be used to determine the length of the astronomical unit? Minor planet is another name for asteroid. asteroid One of thousands of very small members of the solar system orbiting the Sun between the orbits of Mars and Jupiter. Asteroids are often referred to as minor planets. 5. What do we mean by the term "Trojan asteroid?" What is the relationship between the Trojans and the planet Jupiter? What are the Kirkwood gaps and what was Jupiter's role in forming them? Gravitational interactions between asteroids and the planets (and the Sun) lead to collections of asteroids in some places and asteroid-free zones elsewhere. One collection of asteroids is found 60° ahead of Jupiter in its orbit as well as 60° behind. These locations are known as Lagrangian points after the mathematician who predicted their existence. Exactly solving the problem of the gravitational interaction of the Sun, a planet, and an asteroid near it is impossible, but there is an approximate solution valid when the third object is so small that its mass is negligible compared to the masses of the other two objects. This approximation predicts the presence of 5 points which move with the planet around the Sun. Three are on the planet -Sun line - one in the middle, one farther from the Sun than the planet, and one on the opposite side of the Sun from the planet. The other two (known as L 4 and L 5 ) are the ones which lead or follow the planet in its orbit. The 60° angle means that the points form an equilateral triangle (all sides are the same length) - the distance from the objects at L 4 to the planet = distance from planet to Sun = distance from Sun to objects at L 4. These points of stability around Jupiter have collected asteroids known as the Trojan asteroids (purple dots in the figure below). These points exist whenever there are three bodies interacting and one is much larger than the second which is in turn much larger than the third. There are also small meteoroids in front of and behind the Moon which lead and follow it on its trip around the Sun. A sun-observing satellite called SOHO is kept in orbit near L 1 so that it can stay near the Earth for transmission of data. This point allows it to avoid being stuck in & eclipses that happen to satellites which orbit the Earth. Trojan asteroids One of two groups of asteroids which orbit at the same distance from the Sun as Jupiter, 60 degrees ahead and behind the planet. Kirkwood gaps Gaps in the spacings of semi-major axes of orbits of asteroids in the asteroid belt, produced by dynamical resonances with nearby planets, especially Jupiter. 6. What role did gravitational interactions play in the development of asteroid and comet orbits? In the pro- duction of meteroids and the zodiacal light? Rather than condensing where they are now (where the density of objects must have been very low), current theory suggests that these comets were formed in the area of the outer planets but were then caught in gravitational interactions with them & thrown out of the inner Solar System, forming the cloud. Passing stars may disturb this cloud enough to send showers of comets towards the Sun - this kind of mechanism has been suggested as a cause of mass extinctions on the Earth in the past. Even smaller than most meteors are dust particles. There are many of these in the plane of the solar system and they reflect sunlight like anything else. The light from this dust is called zodiacal light (zodiac = plane of ecliptic). The dust should fall into the Sun relatively quickly, so something must be acting to generate more of it. 7. What is a meteor? Distinguish a meteor from a meteorite. What are the two main sources of meteors? meteor is a bright streak in the sky, often referred to as a "shooting star," resulting from a small piece of interplanetary debris entering Earth's atmosphere and heating air molecules, which emit light as they return to their ground states. meteorite Any part of a meteoroid that survives passage through the atmosphere and lands on the surface of Earth. 8. What are the three main types of meteorites? Why is the proportion of stones to irons seen in finds on Earth different from the true proportion in space? From cold temperatures how they become frozen, and to hot temperatures how they can become melted. Almost all meteorites are old. Radioactive dating shows most of them to be between 4.4 and 4.6 billion years old-roughly the age of the oldest Moon rocks brought back to Earth by Apollo astronauts. Meteorites, along with asteroids, comets, and some lunar rocks, provide essential clues to the original state of matter in the solar neighborhood and to the birth of our planetary system. Comets contain many of the basic ingredients for life, but they spend almost all of their time frozen, far from the Sun. A small fraction of the meteorites that survive the plunge to Earth’s surface also contain organic compounds. A similar method is also useful for meteorites the exposed surface is constantly being hit by high-energy particles called cosmic rays these are strong enough to break a nucleus of a heavy element into a few smaller nuclei (ligher elements). By looking at the concentrations of lighter elements in the outer meter or so of the meteorite (that's about as far as the cosmic rays can penetrate), the time since the meteorite was broken off of a larger body can be found. These ages are generally in the tens of thousands to millions of years. Since we believe the Solar System was essentially finished forming billions of years ago, this would suggest that collisions between asteroids are an important source of meteorites. Finally, meteorites may actually show evidence of how the Solar System's formation was triggered. A meteorite found in a Mexican village has been shown to have larger than normal concentrations of a rare isotope of Magnesium (Mg26), which comes from the decay of radioactive Aluminum. The common form of Aluminum is not radioactive, but when elements are exposed to the incredible temperatures and shower of neutrons which explode from supernovae (violent death of a star), they tend to form lots of strange elements. The material in this meteorite could have been formed by being near a supernova when it exploded there is naturally a huge blast wave which accompanies this stellar explosion. In addition to scattering strange elements like this into our neighborhood, the blast wave itself. 9. How do Widmanstatten figures and chondrules provide information on the conditions under which some meteorites were formed? 10. Why do meteor showers repeat themselves year after year in the same part of the sky? Why do meteors in a shower emanate from a single location in space? 11. How do various radioactive decay processes and cosmic ray exposure times give us clues to the forma- tion and history of the solar system? APPLYING YOUR KNOWLEDGE 1. Make a drawing to demonstrate that the Earth encounters more meteoroids after midnight than before midnight. The best time to observe a meteor shower is usually between midnight and dawn. As the Earth orbits the Sun and rotates, we are looking in the backward direction of Earth's orbit before midnight, and in the forward direction after midnight. The exception to the rule is the Geminid meteor shower in December; due to the angle of the debris trail's orbit, the Geminid shower can usually be seen just as well before midnight as after. 2. Would you expect there to be many asteroids having satellites orbiting them? Explain your reasoning. Yes since Astronomers discover a moon orbiting asteroid Eugenia. Most asteroids appear dark and were thought to be composed primarily of rock, which is about three times denser than water. If these asteroids are rubble-piles, it tells us about the severity of collisions in the asteroid belt and its subsequent evolution. If the objects are largely ice, covered with a dark-coating, then these objects may be remnants of burned-out comets and will further our understanding of the connection between comets and asteroids It is almost certain that the satellite was formed by a collision As we know from the formation of our own moon and the craters on planetary surfaces, collisions played a large role in the formation of our solar system. Satellites of asteroids give us a window into these collisions, and help us understand how and why our solar system looks like it does. 3. What arguments might you present to people who believe that comets bring disaster and evil, to con- vince them their ideas are wrong? Before people knew what a comet was, they thought it was an omen from the heavens. They thought it was going to bring disaster. Asteroids or Comets May Have Led to Birth and Death of Dinosaur Era selected near Earth objects (NEO's) with close approaches to Earth in the past and to the year 2100. The probability of any of these objects hitting the Earth on these approaches is essentially zero. There are no known NEO's on a collision course with the Earth. There is a possibility that an as yet undiscovered large NEO may hit the Earth, but the probability of this happening over the next 100 years is extremely small. For comparison with the closest approach data, the distance from the Earth to the Moon is about 0.0026 AU. Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. Known as "minor planets," tens of thousands of asteroids congregate in the so-called main asteroid belt: a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter from approximately 2 to 4 AU (186 million to 370 million miles/300 million to 600 million kilometers). Gaspra and Ida are main belt asteroids. 4. From what you know of comets, would you expect their motions to be immediately apparent to the casual observer? Why or why not? How about for a meteor? Comets are sometimes called dirty snowballs or "icy mudballs". They are a mixture of ices (both water and frozen gases) and dust that for some reason didn't get incorporated into planets when the solar system was formed. This makes them very interesting as samples of the early history of the solar system. When they are near the Sun and active, comets have several distinct parts: nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids; coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus; hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen; dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye; ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind. Comets are invisible except when they are near the Sun. Most comets have highly eccentric orbits which take them far beyond the orbit of Pluto; these are seen once and then disappear for millennia. 5. Meteorites are observed to have an amount of xenon- 129 (129Xe) far in excess of that normally found on Earth. 129Xe comes from the radioactive decay of iodine-129 (129I), which is formed in supernovae explo- sions. Use this information to argue that the forma- tion of the solar system was initiated by the nearby explosion of a supernova. 6. Suppose you came across a rock you thought might be a meteorite. How might you determine whether or not it is a meteorite, given that you had no special equipment? How about if you had all the special equipment you desired? are composed of small grains of rock and appear to be relatively unchanged since the solar system formed. Stony-iron meteorites, on the other hand, appear to be remnants of larger bodies that were once melted so that the heavier metals and lighter rocks separated into different layers. Meteorite Dating - The age of a meteorite can be determined through radioactive dating. This is the same process anthropologists use to date early human settlements, except the anthropologists use different elements. The idea behind this is relatively simple - the atoms of a radioactive element like Uranium-238 (U238) gradually decay into Lead-206 (Pb206) over time. The half-life for this process (time necessary for ½ of some quantity of U238 to decay into Pb206) is about 4.5 billion years. A few things about this are worth mentioning - first, this idea is unlike the effect of aging on humans. We could talk to statisticians working for insurance companies, and they could tell us, very accurately, when half of the people born in any given year will have died - let's say 75 years later. We know, without talking to the insurance company, that 75 years after that, all of those people will have died. In the case of radioactive elements, it doesn't work like that - after one half life, half of the original element will have decayed, and half will remain. After another half life, half of what was left will have decayed, and half will remain (now one quarter of the original amount) and it continues like that. What that means (this is one of the weirdest parts of quantum mechanics!) is that an atom of U238 that is 10 billion years old is just exactly as likely to decay today as is a brand new atom of U 238. Definitely not like people! One thing the element does< have in common with people - just as we can say what fraction of the element will decay in a given time, and the insurance company can say how many people will be alive after a certain time, when it comes to looking at one atom or one person, we have no idea when the atom will decay, and the insurance people have no idea when one person will die. One other interesting thing - notice how much the atomic weight changes during the decay - from 238 to 206! That means 32 neutrons/protons are now gone! Where did they go? They left, at different times, in the form of 8 Helium nuclei which pick up electrons and become ordinary He atoms. By looking at concentrations of different elements in a meteorite, the meteorite can be dated - for example, in an easy case, suppose you find a pocket of metal in the asteroid which is 50% Pb206 and 50% U 238 - it's probably 4.5 billion years old. This assumes that this pocket of metal was all U 238 when it formed - if there was already some lead in it, that would affect your calculations. For that reasons, scientists generally try to use several radioactive elements to arrive at one common age. Most meteorites, when dated, tend to have ages which are about 4.5 billion years. 7. Make a list of easily obtainable household items you might use to make a cometary nucleus. marshmellows toothpicks >9. If the period of Halley's comet is 76 years, approxi- mately what is its maximum distance from the Sun? Relate this distance to that of the planets. Perihelion Distance 0.587 AU >10. What would be the age of a rock in which you measured the ratio of potassium-40 to argon-40 to be 1 to 7? What assumption are you making? Hint: A drawing will be helpful. >11. What would be the age in the previous question if the rock originally contained equal amounts of potassium- 40 and argon-40? > 12. One of the Kirkwood gaps appears at a location where the asteroid's period is exactly one-half Jupiter's orbital period about the Sun. At what distance from the Sun (in AU) is this gap located? Main Belt: located between Mars and Jupiter roughly 2 - 4 AU from the Sun; further divided into subgroups: Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas (which are named after the main asteroid in the group). The most common meteorites, known as ordinary chondrites, are composed of small grains of rock and appear to be relatively unchanged since the solar system formed. Stony-iron meteorites, on the other hand, appear to be remnants of larger bodies that were once melted so that the heavier metals and lighter rocks separated into different layers. Chapter 8 Page 174 SUMMARY QUESTIONS 1. What is the Earth's distance from the Sun? The Earth's diameter? It's average density? astronomical unit (A.U.) The average distance of Earth from the Sun. Precise radar measurements yield a value for the A.U. of 149,603,500 km. the Sun's mass is so great, its distance from Earth is about 400x the Moon's. If we cube 400, we get 400 3 = 64,000,000. if you calculate the Sun's density / Moon's density, you also get 0.42. 2. What is the Moon's distance from the Earth? The Moon's approximate diameter relative to the Earth? It's average density? the Moon, when at full phase, is 180-degrees from the Sun 3. What are the meaning and importance of the concepts of the acceleration of gravity and the escape velocity? escape speed The speed necessary for an object to escape the gravitational pull of an object. Anything that moves away from the object with more than the escape speed will never return. Schwarzschild radius The distance from the center of an object such that, if all the mass compressed within that region, the escape velocity would equal the speed of light. Once a stellar remnant collapses within this radius, light cannot escape and the object is no longer visible. 4. How do seismic data give us information about the interiors of the Earth and Moon? What were the results of the lunar seismology experiments? Some paths followed by seismic waves from the site of an earthquake. Some of the waves called shear, or S-waves, and colored red in the figure are blocked by Earth's outer coure. The result is the shadow zone shown. The explanation for this behavior is that these particular waves cannot pass through liquid. The observation that every earthquake exhibits these shadow zones is the best evidence we have that the outer core of our planet is liquid. There is also evidence that some waves (pressure, or P-waves, shown in green), which can pass through the liquid outer core, are reflected off the surface of a solid inner core, of radius 1300 km. differentiation Variation with depth in the density and composition of a body, such as Earth, with low-density material on the surface and higher density material in the core. Earth, then is not a homogeneous ball of rock. Instead, it has a layered structure, with a low-density rocky crust at the surface, intermediate-density rocky material in the mantle, and a high-density metallic core. This variation in density and composition is known as differentiation. Earthquakes. 5. What are the various layers of the Earth's interior and their important properties? lithosphere Earth's crust and a small portion of the upper mantle that make up Earth's plates. This layer of the Earth undergoes tectonic activity. 6. What is continental drift and what produces it? How is volcanism related to it? Plate tectonics The slowly drifting gigantic plates or slabs of Earth's surface, and that these plates are slowly drifting around the surface of our planet. These plate motions, popularly known as continental drift, have created the mountains, oceanic trenches, and many other large-scale features across the face of planet Earth. Earthquakes and volcanic eruptions 7. What chemical elements make up the Earth's atmos- phere? What is the percentage of each? magnetosphere A zone of charged particles trapped by a planet's magnetic field, lying above the atmosphere. hydrogen gas gases 8. What is the greenhouse effect, and how is it produced? greenhouse effect The partial trapping of solar radiation by a planetary atmosphere, similar to the trapping of heat in a greenhouse. 9. Where did the Earth's current atmosphere come from? Why do scientists believe it is not the same as the original atmosphere? atmosphere Layer of gas confined close to a planet's surface by the force of gravity. 10. What is the Earth's magnetosphere? Describe its appearance. What effect does the magnetosphere have on charged particles in its vicinity, and what is its role in producing an aurora? magnetosphere A zone of charged particles trapped by a planet's magnetic field, lying above the atmosphere. 11. How did astronomers know the Moon lacked an atmosphere before NASA sent spacecraft there? Lacking the moderating influence of an atmosphere, the Moon experiences wide variations in surface temperature. Noontime temperatures can reach 400 K, well above the boiling point of water (373 K). At night (which lasts nearly 14 Earth days) or in the shade, temperatures fall to about 100 K, well below water's freezing point (273 K). 12. What are the characteristics of the various types of lunar surface features? Describe how these features formed and present evidence in favor of the formation mechanism. How does the appearance of the lunar near side differ from that of the far side? The far side of the moon does look noticeably different from the near side. The far side is heavily cratered & does not seem to have maria. (The far side has been explored by satellites - also, we can see a small portion of it due to several effects which combine to show us a total of 60% of the moon's surface (over time) rather than the 50% we might expect). The reason is probably that the moon formed inside Earth's gravitational field and some differentiation was caused by it; the heavier material was drawn towards the Earth, while the lighter material was pushed away from it. The crust is light material, so the crust on the far side is thicker & therefore harder for lava to penetrate - it's easier for it to just go through the thinner crust on the Earth side. The largest of them (Mare Imbrium, the "Sea of Showers") is about 1100 km in diameter. Today we know that the maria are actually extensive flat plains that resulted from the spread of lava during an earlier, volcanic period of lunar evolution. In a sense, then, the maria are oceans-ancient seas of molten lava, now solidified. The older highlands are much more heavily cratered than the younger maria. Knowing the ages of the highlands and maria, researchers can estimate the rate of cratering in the past. 13. What basic types of rock are found on the Moon? What are the implications of these rock types for the origin and history of the Moon? Four Types of Lunar Rocks Mare Basalts The first lunar samples brought back by Apollo 11 from Mare Tranquillitatis were black volcanic basalts. The basalts came from different depths beneath the surface, spilling out onto the mare surface as very uid lava, filling up the large impact basins of the Moon. They have ages ranging from 3.2 to 3.9 billion years. Impact Breccias Breccias are composite rocks made by the solidification of a mix of sand and gravel sized pieces of various rocks. They were formed by impact events, which first shattered and then compacted pieces of rock from different places, welding them together Pristine Highland Rocks As their name implies, pristine highland rocks are rocks col- lected mainly in the lunar highlands that have not been sub- stantially altered by impacts or reheating since they were first formed. These rocks may represent material from the original lunar crust that formed between 4.6 and 4.3 billion years ago. Regolith The lunar regolith is a loose soil that covers the Moon from a depth of a few meters on the mare, to a few tens of meters on the highlands. From cold temperatures how they become frozen, and to hot temperatures how they can become melted. Almost all meteorites are old. Radioactive dating shows most of them to be between 4.4 and 4.6 billion years old-roughly the age of the oldest Moon rocks brought back to Earth by Apollo astronauts. Meteorites, along with asteroids, comets, and some lunar rocks, provide essential clues to the original state of matter in the solar neighborhood and to the birth of our planetary system. Radioactive dating indicates ages of more than four billion years for highland rocks, and from 3.2 to 3.9 billion years for those from the maria. 14. What is the probable scenario for the early history of the Moon's surface as determined from the evidence provided by radioactive dating? Radioactive dating indicates ages of more than four billion years for highland rocks, and from 3.2 to 3.9 billion years for those from the maria. The older highlands are much more heavily cratered than the younger maria. Knowing the ages of the highlands and maria, researchers can estimate the rate of cratering in the past. 15. What are the four main ideas of the Moon's origin? Describe them and give the evidence for and against each hypothesis. Which one is most likely to be valid? Explain why. Moon formation theories- there are several theories about the origin of the moon. One is the fission hypothesis, which says that the rapidly spinning Earth ejected the moon from the site of the Pacific ocean billions of years ago. Reasons this hypothesis is unlikely include 1) material thrown from Earth would probably have fallen back to Earth, 2) the moon should've been thrown into the Earth's equatorial plane rather than the ecliptic plane since the rotation of Earth on its axis has nothing to do with its orbit, and 3) connecting the site to the Pacific ocean makes no sense because, due to plate motion, the site of the Pacific ocean didn't exist billions of years ago. A second hypothesis is the capture hypothesis, which suggests the moon was captured by the Earth. While a capture is not impossible (although it is unlikely), a third body has to be involved to get rid of the excess energy. The accretion hypothesis suggests that the moon formed gradually in the same way the Earth did. If it formed at the same time as the Earth, though, it should have essentially the same composition. The chemical composition of moon rocks is noticeably different than those of the Earth, though - it has rocks with high concentrations of potassium, phosphorous, and rare-earth elements. The difference could possibly be explained by assuming that the moon formed at a different time when the conditions around the Earth had changed. A more recent theory that may work even better is the giant impact theory. This theory says that the early Earth was involved in a huge collision with an object approximately the size of Mars and a huge amount of material was thrown into orbit around the Earth. This material eventually assembled itself into the Moon. Advantages of this theory would be the ability to explain the moon's lack of iron (it was all in the Earth's core, and the impact was not enough to eject material from Earth's core). and its lack of volatile elements (the incredible temperatures involved in such an impact would boil them all away rapidly). Today, many astronomers favor a scenario often called the impact theory, which postulates a glancing collision between a large, Mars-sized object and a youthful, molten Earth. Computer simulations of such a catastrophic event show that most of the bits and pieces of splattered Earth could have coalesced into a stable orbit, forming the Moon. 16. Why does the Moon produce two tidal bulges on the Earth? What are the long-term effects of tides on the Earth-Moon system? Basically the same process is responsible for the Moon's synchronous orbit. Just as the Moon raises tides on Earth, Earth also produces a tidal bulge in the Moon. Indeed, because Earth is so much more massive than the Moon, the lunar tidal bulge is considerably larger and the synchronization process correspondingly faster. The Moon's orbit became synchronous long ago-the Moon is said to have become tidally locked to Earth. Most of the moons in the solar system are similarly locked by the tidal fields of their parent planets. APPLYING YOUR KNOWLEDGE 1. Compare and contrast the processes that modify the surfaces of the Earth and the Moon. Consider separately processes that occur internally as well as those involving externally produced events. Moon's Surface - the moon is covered by large dark areas named maria (seas) by Galileo - it's not an unreasonable guess to think these areas are water when seen through a small telescope, but they're actually the remains of old lava flows. These were triggered by the impact of large objects from space (objects tens of km in size or more) slamming into the young moon and the filling of the crater by a lava flow. The lava flows probably came from fissures in the moon since most of these maria have no volcanic cones nearby. The other prominent features on the moon are the craters. Many of these are the result of countless impacts since the formation of the moon. Some are so severe that the material thrown up from the initial impact was large enough and thrown high enough to create secondary craters & crater chains. Central mountain peaks inside the craters can also be formed as the ejected material falls back to the surface. While the moon doesn't have large volcanic mountains, it does have volcanic domes which form some of the craters. When magma comes to the surface and the surface cools, it forms a dome. The magma can then retreat back towards the center of the moon or planet, and the dome may later collapse and form a crater. The surface remains heavily cratered because the Moon did not have a crust-recycling system, and the only way craters are removed is through bombardment by cosmic rays and tiny meteoroids (or large ones) which gradually remove the features. This makes the top layer of the surface very dusty - it's called regolith. the surfaces of the Earth the surface mountains, oceanic trenches,and other large-scale features on Earth's surface. and the Moon have lunar rocks, and the highlands, and the lowlands. the Moon had mountains, valleys, and creates-terrain in many ways reminiscent of that of Earth. 2. Apply the idea that theories cannot be proven true, only falsified, to the hypotheses of lunar formation discussed in the chapter. What is your conclusion? The largest of them (Mare Imbrium, the "Sea of Showers") is about 1100 km in diameter. Today we know that the maria are actually extensive flat plains that resulted from the spread of lava during an earlier, volcanic period of lunar evolution. In a sense, then, the maria are oceans-ancient seas of molten lava, now solidified. 3. Because the Earth's atmosphere consists of 78% nitrogen (N2), why does the atmosphere not have substantial amounts of ammonia (NH3), as does Jupiter? The lunar surface has a lack of wind and water on the airless Moon. Despite this barrage from space, the Moon's present-day erosion rate is still very low-about 10,000 times less than on Earth. Lunar Surface The lunar surface is not entirely changeless. Despite the complete lack of wind and water on the airless Moon, the surface has still eroded a little under the constant "rain" of impacting meteoroids, especially micrometeoroids. Jupiter is a bigger jovian outer planet and is composed of more gases. 4. Consider each rock type. If specimens of each type were found on a given planetary body, what would you be able to conclude about conditions and pro- cesses on and within that body? Radioactive dating indicates ages of more than four billion years for highland rocks, and from 3.2 to 3.9 billion years for those from the maria. The older highlands are much more heavily cratered than the younger maria. Knowing the ages of the highlands and maria, researchers can estimate the rate of cratering in the past. 5. How might the Earth have differed if it had been 0.7 AU from the Sun rather than where it is now? The Earth would be warmer.and more dry surface. 6. The Earth's tidal force acting on the Moon has slowed the Moon's rotation to the point where it is synchro- nous (the same face always faces the Earth). Given that the Moon also exerts a tidal force on the Earth, why is the Earth not in synchronous rotation? synchronous orbit State of an object when its period of rotation is exactly equal to its average orbital period. The Moon is in a synchronous orbit, and so presents the same face toward Earth at all times. Basically the same process is responsible for the Moon's synchronous orbit. Just as the Moon raises tides on Earth, Earth also produces a tidal bulge in the Moon. Indeed, because Earth is so much more massive than the Moon, the lunar tidal bulge is considerably larger and the synchronization process correspondingly faster. The Moon's orbit became synchronous long ago-the Moon is said to have become tidally locked to Earth. Most of the moons in the solar system are similarly locked by the tidal fields of their parent planets. 7. Describe a baseball game being played on the Moon. Include discussions of the distance the ball might be hit, the strides of the base runners, the ease or difficulty of fielding the ball, the likelihood of a rain check or calling the game due to darkness, and how the fans might boo the umpire. The lunar surface has a lack of wind and water on the airless Moon. Despite this barrage from space, the Moon's present-day erosion rate is still very low-about 10,000 times less than on Earth. Lunar Surface The lunar surface is not entirely changeless. Despite the complete lack of wind and water on the airless Moon, the surface has still eroded a little under the constant "rain" of impacting meteoroids, especially micrometeoroids. Composition of the tenuous lunar atmosphere is poorly known and variable, these are estimates of the upper limits of the nighttime ambient atmosphere composition. Daytime levels were difficult to measure due to heating and outgassing of Apollo surface experiments. >8. Suppose you measured g to be 1000 cm/sec2. What, then is the mass of the Earth? >9. Compute the escape velocities of the Earth and Moon. How much larger is the Earth's escape velocity? (Use data for the Moon from Table 8-3.) Earth Escape velocity (km/s) 11.186. Moon Escape velocity (km/s) 2.38 >10. Because the uncertainty in the time for a laser beam to reach the Moon and back is about a billionth of a second, compute the uncertainty in the distance by finding how far light travels in a billionth of a second. >11. Using Figure 8-17, determine the diameter of Mare Serenitatis, the Sea of Serenity. Mare is about 1100 km in diameter. Today we know that the maria are actually extensive flat plains that resulted from the spread of lava during an earlier, volcanic period of lunar evolution. In a sense, then, the maria are oceans-ancient seas of molten lava, now solidified. >12. What would be the period of a satellite in orbit about the Earth if the satellite were 385,000 km from it? The Moon orbit: 384,400 km from Earth diameter: 3476 km mass: 7.35e22 kg >13. Assuming the South American and African plates have always moved with the same speed they are moving today, compute how long ago the continental land masses were joined. (Make a reasonable esti- mate of their current separation.) >14. Explain how you might go about computing the height of the central peak shown in Figure 8-19. What information would you need to have? Chapter 9 Page 202 SUMMARY QUESTIONS 1. What are the major facts known about each of the terrestrial planets? Include distances, general orbital characteristics, size, mass, and density relative to the Earth; and temperature, atmospheric composition, etc. Terrestrial planets are close to the Sun closely spaced orbits small masses terrestrial planet The four innermost planets of the solar system, resembling the Earth in general physical and chemical properties. The Earth-like Planets The four planets closest to the Sun have a variety of similarities. For that reason, they're generally grouped as the terrestrial planets. While Venus & Mars are among the brightest objects in the night sky, Mercury has always been hard to study due to its closeness to the Sun. It's never more than about 27° from the Sun, which means it is often lost in the glare of the Sun. While Venus is easy to find & observe through optical telescopes, surface features can't be seen due to the thick cloud cover (the atmospheric pressure is about 100x ours - that's the same as being about 1 km under the ocean!). The phases are easily observed, and were first noticed by Galileo. Venus stays within about 47° of the Sun at all times (so what would be the latest after sunset you would be able to see Venus?). Another problem with ground-based observations of Venus is that its synodic period, which dictates when it will be closest to us, is almost exactly 5 times its "solar day". In other words, every time Venus is at inferior conjunction, we see essentially the same side of it, making radar mapping from Earth very hard! 2. Compare and contrast all the terrestrial planets with one another. In the discussion, include any distinctive features of orbital characteristics, appearance, rota- tion and revolution, general atmospheric features and composition, interior structure, magnetic fields, and satellite systems. Mar's small size means that any internal heat would have been able to escape more easily than in a larger planet like Earth or Venus. It is too cold on Mars. The magnetic field is to weak. cratered surfaces appear on earth, and mars due to asteroid impacts, meteors impacts. Mars Seasonal changes of Martian markings, climatic changes; seasonal winds and summer dust storms. Surface features huge volcanoes, riverbeds, and channels. Evidence of past liquid water. Eroded craters. Very little, if any, plate tectonics. The Tharsis region and Valles Marineris show sign of surface cracking which may be associated with pressures on the crust from below, but no sliding motion as in plate tectonics. Sun Earth Mars Water once flowed on Mars as the evidence is Two types of flow features are seen: runoff channels, and outflow channels. There is no evidence for liquid water anywhere on Mars today. Most likely if there is water on Mars? The water is locked in a layer of permafrost, which is water ice lying just below the planet's surface, with some more water contained in the polar caps. Mar's small size means that any internal heat would have been able to escape more easily than in a larger planet like Earth or Venus. It is too cold on Mars. The magnetic field is to weak. Venus 3rd planet from the Sun. Earth When Earth formed, any atmosphere it might have had-sometimes called the primary atmosphere-would have consisted of the gases most common in the early solar system: light gases such as hydrogen, helium, methane, ammonia, and water vapor. Mars Presumably, Mars also had first a primary and then a secondary (outgassed) atmosphere early in its history. Around 4 billion years ago, Mars may have had a fairly dense atmosphere, perhaps even with blue skies and rain. Venus Venus's dense atmosphere is made up almost entirely of a prime greenhouse gas, carbon dioxide. Venus is hot because of the greenhouse effect. Venus' extremely high temperatures and Mars' extremely low temperatures are examples of a runaway greenhouse effect. 3. What planetary features were Earth-bound astrono- mers able to see through their telescopes on each of the terrestrial planets? Describe any changes in these features that astronomers could have observed. resembling the Earth in general physical and chemical properties. Surface features with craters, and canals. Volcanoes. Mars is easily seen through a telescope, and surface features can also be seen due to the lack of a thick atmosphere (only about 1/100 the pressure of ours - about what it is 34 km above the ground!). The most obvious features visible on Mars are the polar ice caps and many lines or channels which, when first observed, were translated from Italian as & canals. This led some people to believe they had been constructed to bring water from the polar regions by some kind of intelligent life. Mercury Rotation of Mercury- Earth-based radar observations of Mercury in the 1960's revealed that Mercury's day was not the same length as its year, as had been assumed before then. It was thought that since Mercury was so close to the Sun, tidal locking had forced it into synchronous rotation the same way the Earth forced the Moon into synchronous rotation. The radar data showed that the day length was 59 days compared to the orbital period of 88 days. The explanation goes like this: if the day and the year of a body (periods of rotation & revolution, but we'll call them day & year for convenience) are the same, that means the body rotates 360° on its axis while it moves 360° around its primary. The difficulty arises from Kepler's 3rd law. Rotational speed (day length) can't change significantly around the orbit, but we know from Kepler's 3 rd law that orbital speed does change in an elliptical orbit. The body will change orbital speed, but can't change rotational speed. Incidentally, this is one of the reasons we can see more than 50% of the Moon's surface over time - the speeds don't exactly coincide all the time, so we get slightly different views of the surface.

    Mercury has an orbit that is noticeably more eccentric than the Moon's (0.206 vs. 0.055). This means the orbital speed changes significantly during that 88 day orbit, and the rotational speed just can't change like that. If the rotation were synchronous when Mercury is closest to the Sun, the rotation would be too fast when Mercury is far from the Sun, and if it were synchronous at aphelion (greatest distance from Sun), it would be too slow at perihelion (closest to Sun). The way the Sun & chooses where to lock the rotation is connected to the strength of tidal forces - they're strongly dependent on distance, so perihelion is where Mercury feels the strongest tides. Rotation is synchronous based on Mercury's speed at perihelion. A day length that is 2/3 of the year length (this simple fractional relationship between the two will come back when we look at asteroids and resonance) means Mercury will have made one and a half rotations on its axis from perihelion to perihelion. That means that Mercury will show the exact opposite face to the Sun on that pass. Since the tidal bulges are symmetric, one or the other of the bulges will always point towards the Sun at perihelion. We can use what we know about the connection between solar & sidereal days to find out something else about Mercury. When we looked at the Earth, we saw that, relative to the stars, we have one more rotation on our axis each year than we do relative to the Sun. That's why there are 365 solar days in a year, but 366 sidereal days. The difference is much greater on Mercury. The year on Mercury is made up of 1 ½ sidereal days. Subtract one and you get ½ solar day per year. In other words, the time between successive passages of the Sun through your meridian on Mercury would be 176 days = 2 orbits = 2 years! This strange arrangement, together with Mercury's axial tilt of less than 1°, means that Mercury doesn't have seasons. Mercury has essentially no atmosphere, which is a result of the very high temperatures on the sun-facing side of Mercury ( 600 K, or over 650 F) combined with Mercury's small mass. The planet is very dense, suggesting that it has an iron core which is very large, relative to its overall size. Earth has a slightly higher average density than Mercury (5515 kg/m 3 vs. 5430 kg/m 3), but Earth & to do this. Earth is so large (compared to Mercury), its gravity tends to compress its iron core to higher densities than we would find for iron on Earth's surface. Mercury has much less mass, so it can't compress its core to the same extent. If we could remove the compression Mercury does produce, its density would be 5300 kg/m 3, almost what it is now. Earth, on the other hand, would have a density of only 4400 kg/m 3 if we removed compression. This means Mercury's iron core takes up a much larger fraction of its interior than Earth's does. This large iron core is assumed to be the source of Mercury's magnetic field (only 1% of Earth's, but still surprisingly large considering how slowly Mercury rotates). The surface of Mercury has been found to be heavily cratered, as would be expected for a small body without any atmosphere or weathering or plate tectonic activity. The cratering is slightly different from the patterns on the Moon, probably because Mercury's stronger gravity would keep debris from flying as far after an impact. There have been some incredibly strong hits on Mercury. The Caloris basin, over 1300 km in diameter, is evidence of one. This impact was so great that the ground on the opposite side of the planet is jumbled as a result of it called weird terrain. When the crater formed, shock waves were sent all through Mercury and they converged on the opposite side in a kind of super-earthquake activity. While there is evidence of lava flowing on Mercury billions of years ago, it is essentially dead geologically - no mountains, active volcanoes, plate tectonic activity, or even plates. Mercury is hard to see because its orbit is much smaller than ours, and therefore it is always relatively close in angular terms to the Sun. At its maximum elongation the point where it is as far from the Sun as possible, seen from Earth, it is only about 27° away from the Sun. Venus is much easier to see than Mercury for several reasons: it's larger, it's closer to us, it's still close to the Sun, and it reflects 59% of the light falling on it, compared to 12% for Mercury (this is called the albedo - Earth's is 39% and the Moon's is 11%). All of this combines to make Venus the 3rd brightest object in the sky, after the Sun Moon. Venus, like Mercury, stays close to the Sun at all times. Since its orbit is larger, it reaches 47° at maximum elongation. This means it is never seen more than about 3 hours before sunrise, or 3 hours after sunset. For this reason, it's called the evening star (or, when it's on the other side of the Sun as seen from Earth, the morning star). While Venus is easy to find & observe through optical telescopes, surface features can't be seen due to the thick cloud cover (the atmospheric pressure is about 100x ours - that's the same as being about 1 km under the ocean!). The phases are easily observed, and were first noticed by Galileo. Incidentally, the fact that Venus has phases means it can't be orbiting Earth and that it must be orbiting the Sun instead. We can use radar to see through Venus' cloud cover, but observations from Earth are slightly frustrated by the fact that Venus' synodic period is 583.9 days, while its solar day is 116.8 days. This means that every time Venus is in inferior conjunction (when it's closest to us & logically easiest to map via Earth-based radar), it has been through almost exactly 5 solar days since its last inferior conjunction, so it's showing us almost exactly the same face! This weird solar day is found by using a relatively simple formula which relates a planet's sidereal orbital period P, sidereal rotation period R, and solar day D For example, for Earth, we have D = 1 solar day and P = 365.25 solar days, so we can solve for R and get (1/1) + (1/365.25) = 1/R, so 1/R = 1.002737 and R = 0.9973 days. That works out to 23 hours, 56 minutes, just as we saw earlier. The weird part about Venus' rotation is that it is retrograde (backwards relative to just about everything else in the solar system). This means its sidereal day should be negative in the formula above. There are no seasons on Venus because of this slow rate of rotation, combined with the thick cloud cover and the small axial tilt of 3°. Also, Venus moves so slowly that we don't expect a strong magnetic field. In the late 1970's, the Pioneer series sent probes down through the atmosphere of Venus, where they transmitted information until the incredible pressure, heat (about 700K or about 800 F), and corrosive atmosphere (which includes sulfuric & hydrofluoric acid) destroyed them. A decade later, Magellan was sent to Venus to map it using cloud-penetrating radar. Both observation and theory suggest that the constant high temperatures on Venus give the surface a putty-like quality that tends to round off mountains as they gradually flow back down to the lower levels of the planet. This plasticity in the rocks may also explain the lack of plate tectonic activity on Venus. Some of the mountains on Venus are even larger than Earth's, however, and the surface does show evidence of volcanic domes, flow channels, and continent-like structures. The volcanic activity may provide Venus with a new surface every few hundred million years - the large-crater formation rate is much smaller than the Moon's, which suggests a young (less than a billion years - maybe much less) surface. There aren't really any small craters on Venus (less than 3 km across), probably because the atmosphere is so incredibly dense that anything small would burn up on the way down. Apparently absent on Venus is any evidence of plate tectonics. Venus, like Earth and Mars, developed its current atmosphere (the second one) as a result of outgassing or gases coming from the planet itself. Volcanoes are the primary source of this atmosphere, and the gases produced include CO 2 and sulfur compounds. Venus' atmosphere is in fact about 95% CO 2 , and is many times more dense than Earth's. Mars' atmosphere is also about 95% CO2, but it far less dense than Earth's. How did these neighboring planets end up with atmospheres so different from ours (only about 0.03% CO2)? The main reasons are water and life. CO2 dissolves very easily in the liquid water covering the Earth. Water can help rocks absorb CO2 and make carbonates. Life in the oceans would have used carbonates to build shells, which sink to the bottom of the ocean when the organisms die. In this way, the oceans and rocks have trapped huge amounts of CO2 on the Earth. Also, plant life has been processing CO2 into O2 for billions of years. Finally, when the plants and animals die, they return nitrogen to the air.

    Why didn't this happen on Venus? Venus was probably too hot for liquid water. The CO 2 and water vapor in the air act to raise the temperature even more through the greenhouse effect and any trapped CO 2 would be released to add to the problem. We're about to see a very rare event connected with Venus. While inferior conjunctions of Venus happen fairly often (every synodic period), Venus rarely moves across the face of the Sun as seen by the Earth (the tilts of the orbits are different). This event is called a transit, and there wasn't one in the entire 20th century. Transits of Venus occur in pairs separated by an 8 year period, with an interval of over 100 years between two pairs. Transits of Venus helped determine the size of the solar system by providing a way to convert AU's into Earth diameters. The distance to Venus during a transit is just 1 AU (Earth to Sun) - 0.723 AU (Venus to Sun). Parallax measurements taken from opposite sides of Earth gave the distance to Venus in terms of Earth's diameter, which was well known by then. Until this was done, astronomers had only a rough idea of how big an AU really was. The next transits of Venus will be on June 8, 2004 and June 6, 2012 (notice that the time between these two events is a whole number of synodic periods, as it must be). Transits of Mercury happen more often, and we'll get our next one on May 7, 2003. Mars is easily seen through a telescope, and surface features can also be seen due to the lack of a thick atmosphere (only about 1/100 the pressure of ours - about what it is 34 km above the ground!). The most obvious features visible on Mars are the polar ice caps and many lines or channels which, when first observed, were translated from Italian as & canals. This led some people to believe they had been constructed to bring water from the polar regions by some kind of intelligent life. These ice caps are made of a combination of ordinary ice and dry ice (solid CO 2) and provide evidence of seasons on Mars which are more like our own. Mars has a 25° tilt and a day which is about the length of ours (much shorter than its year). Seasonal changes in the ice caps are visible from telescopes, the ice that's melting (actually sublimating - going directly to a gas) is mostly CO 2 - it doesn't get warm enough at the poles to melt the water ice. Therefore, the ice caps on Mars are of two kinds - seasonal and permanent. The seasonal ones are dry ice (frozen CO 2). When summer arrives, the temperature climbs high enough to allow the dry ice to sublimate to a gas, but the permanent caps (leftover dry ice and water ice) remain.

    In the distant past, things were different. The surface of Mars actually shows evidence of huge floods. Although there is apparently no liquid water on Mars now, it is believed that the Martian landscape has water trapped in the form of permafrost. Over long timescales, the climate may change on Mars just as it seems to do on Earth (ice ages). When the temperature is high enough, the water can be freed from the permafrost and/or cause landslides in it. Other surface features include volcanoes (tallest in the Solar System - about 3x as high as the highest mountains on Earth), continent-like areas, and ancient lava flows. The volcanoes on Mars are dead now, but how did they get so big? First, plate motion was nonexistent, so upwellings of the kind that created the Hawaiian islands wouldn't have formed a chain of volcanoes - it would've been one large peak instead (we get a chain of islands on the Earth because plate motion drags a plate across a hot spot, making islands as it goes. No movement means all the building happens in the same location). Also, the surface gravity on Mars is about 1/3 of Earth's, so it seems reasonable that volcanoes could grow 3 times larger there, as the force of gravity is what would be expected to drag them back down to lower levels. The current climate on Mars provides a look at the greenhouse effect moving in the other direction. First, due to the smaller size therefore more rapid cooling, Mars "died" geologically long ago. Volcanic eruptions are the likely source for the CO 2 in the atmospheres of the terrestrial planets (except Mercury, of course), so a shorter period of volcanic activity translates into a thinner atmosphere. Mars' low gravity gives a low escape velocity for gases, means Mars' atmosphere is only about 1% as dense as Earth's. This lower amount of CO 2 was much less efficient at trapping heat (and since Mars is both smaller than and twice as far from the Sun as Venus, it receives well under ¼ as much energy from the Sun anyway). Temperatures on Mars would be lower, and that would tend to take water vapor out of the air - we're all familiar with how dry the air is in winter compared to summer. As the water vapor comes out of the air, the temperature drops even more. The greenhouse effect & runs away in the other direction, with the overall result being that the water on Mars is now apparently frozen into ice. Mars has very weak magnetic field of around 0.1% of the Earth's. Since it rotates relatively rapidly (24.6 hours), this probably means that the core is low in iron and/or has already solidified and only the field trapped in the rocks remains. Mars also has the distinction of being the only terrestrial planet other than Earth to have moons. It has two very small satellites, Phobos & Deimos, which are about 23 & 12 km in diameter. Phobos goes around with an incredibly fast 7 hour period! Deimos has a period of about 30 hours. Mars. This planet is harsh by Earth standards-liquid water is scarce, the atmosphere is thin, and the lack of magnetism and of an ozone layer allows solar high-energy particles and ultraviolet radiation to reach the surface unabated. But the Martian atmosphere was thicker, and the surface warmer and much wetter, in the past. The Viking landers found no evidence of life Water canals or canals created by erosion. 4. What do we mean by the runaway greenhouse effect? Why do we think the atmospheres of Earth and Venus developed as they did? What is the critical role of life in the maintenance of Earth's atmosphere? runaway greenhouse effect A process in which the heating of a planet leads to an increase in its atmosphere's ability to retain heat and to further heating, quickly causing extreme changes in the temperature of the surface and the composition of the atmosphere. Earth When Earth formed, any atmosphere it might have had-sometimes called the primary atmosphere-would have consisted of the gases most common in the early solar system: light gases such as hydrogen, helium, methane, ammonia, and water vapor. Venus Venus's dense atmosphere is made up almost entirely of a prime greenhouse gas, carbon dioxide. Venus is hot because of the greenhouse effect. 5. Describe the history of Martian "canals," paying attention not only to the objective evidence prior to Mariner also to possible "nonobjective" aspects. Mars is easily seen through a telescope, and surface features can also be seen due to the lack of a thick atmosphere (only about 1/100 the pressure of ours - about what it is 34 km above the ground!). The most obvious features visible on Mars are the polar ice caps and many lines or channels which, when first observed, were translated from Italian as & canals. This led some people to believe they had been constructed to bring water from the polar regions by some kind of intelligent life. APPLYING YOUR KNOWLEDGE 1. In what ways might Earth and Mars have been different than they currently are if each exchanged places with the other; in other words, if a Mars-sized body were 1 AU from the Sun and an Earth-sized body at 1.5 AU? Earth maybe dry, and cold, and Mars maybe supporting all kinds of life with oceans of water, and active volcanoes. Life-does it exist elsewhere in the universe and not just on Earth? Martian meteorite. Martian Metereorite ALH84001, weighing about 2kg, was recovered in Antartica in 1984. The thin black coating on its surface ("fusion crust") was formed when the rock fell through Earth's atmosphere. In a room facing the entrance to UNM's Northrop Hall is the IOM Meteorite Museum. Inside. Artifacts from the solar system's birth 4.6 billion years ago, far older than any rocks on Earth, meteorites are among nature's true rarities. At present, the Museum's collection includes approximately 600 meteorites, some large but most small-about one-sixth of all the meteorites in the world, excluding those found in the Sahara or Antarctica. some meteorites are rarer still. At least 95 percent of all meteorites originated in the asteroid belt; those from elsewhere, such as the moon or Mars, are especially valuable. A piece of a lunar meteorite is worth about $5,000 a gram. When you think about how the solar system formed, it all started out with dust Speck by speck, one clinging to another, then another, accreting inexorably, growing in mass and gravity, eventually becoming the matter comprising almost everything in the solar system, including the planets-and us. is there any place where specks of the primordial dust might still be found? The only way to preserve this primordial dust is to place it in cold storage in accreted ice. The nuclei of comets, which have been called "dirty snowballs," preserve the original cosmic dust. Transmission Electron Microscope to analyze each particle. trying to figure out where it's from. Martian impact craters might have been collecting basins for water, or perhaps have intersected hydrothermal underground aquifers, where life might form. compare the chemistry of Martian soils with those around volcanic and hydrothermal vents on Earth. using the Secondary Ion Mass Spectrometer a instrument able to identify trace elements in very small samples to analyze Lunar samples from the Apollo 14 Mission. The samples are from the earliest magmatism on the moon, and looking at them can help tell us how the moon evolved. 2. Examine Figure 9-5a. How do you know that this is a picture of Mercury and not the Moon (other than because the figure caption tells you so)? 3. Why does the fact that Venus has a dense core lead to our expectation that the surface rocks probably have a low iron content? The distance to Venus during a transit is just 1 AU (Earth to Sun) - 0.723 AU (Venus to Sun). 4. On Earth a solar day is a little longer than a sidereal day, on Venus it is shorter. Explain why. Hint: Use a carefully made drawing. On Earth When we looked at the Earth, we saw that, relative to the stars, we have one more rotation on our axis each year than we do relative to the Sun. 365 solar days in a year, 366 sidereal days. On Venus Venus' synodic period is 583.9 days, while its solar day is 116.8 days. 5. You have just landed on Mars. Your view is that of Figure 9-12. Describe the view vividly and in detail. The surface of Mars is of rocks a rocky terrain. 6. The photographs of Venus in Figure 9-2 are at the same scale. Assume the first one was taken when Venus was at its greatest distance from the Earth, and the last one when it is nearly at its closest approach. Make a drawing of the orbits of Earth and Venus, and mark and label the positions corresponding to the photographs. Venus at it's greatest distance from the Earth Venus at it's closest approach from the Earth 0.3 A.U. 45,000,000 km from Earth. With this information, we can compute the magnitude of the astronomical unit: 0.3 A.U. is 45,000,000 km, so 1 A.U. is 45,000,000 km/0.3, or 150,000,000 km. >7. If Mercury's angular diameter is observed to be 0.002 degrees when its distance from Earth is 0.92 AU, what is Mercury's diameter? Express the diameter in kilometers, in units of the Earth's diameter, and in terms of the Moon's diameter.. 0.002 + 0.92 =0094 0.002 x 0.92 0004 0018 000 =.00184 >8. Use the planetary orbital periods in Table 9-1 or Appendix C to calculate the distances of the terrestrial planets from the Sun in AU. >9. How much would a 150-pound person weigh on each of the terrestrial planets, as well as on the Moon? >10. Deimos circles Mars at a distance of 23,500 km in 1.26 Earth days. Calculate the mass of Mars, and compare your value with the "true" value. What is the percentage difference? >11. Under the best observing conditions on Earth, the smallest angle astronomers can discern is about 0.25 seconds of arc. Assuming Martian "canals" must have at least this angular size, compute their true size in kilometers. Is such a size reasonable for channels produced by intelligent beings? >12. The photographs of Venus in Figure 9-2 are at the same scale. Assuming the first one was taken when Venus was at its greatest distance from Earth, and the last one when it is nearly at its closest approach, determine the ratio of greatest to least distance from Earth. Does your answer make sense in view of what you know about Venus's orbit? >13. Compute the size in kilometers of the smallest Martian feature on the photographs in Figure 9-3. Chapter 10 Page 234 SUMMARY QUESTIONS 1. In what ways are each of the Jovian planets similar to and different from one another? In your discussion, include the orbital characteristics, appearance, rota- tion and revolution, general atmospheric features, and chemical composition. differential rotation The tendency for a gaseous sphere, such as a jovian planet or the Sun, to rotate at a different rate at the equator than at the poles or for the rotation rate to vary with depth. For a galaxy or other object, a condition where the angular speed varies with location within the object. is normal for fluid bodies such as the jovian planets. The amount of differential rotation on Jupiter is small-the equatorial regions rotate once every 9h 50m, while the higher latitudes take about 6 minutes longer. The jovian planets are massive enough to have retained even the lightest gas, hydrogen, and very little of their original atmospheres have escaped since the birth of the solar system 4.6 billion years ago. The colors of Saturn's cloud layers, as well as the planet's overall yellowish coloration, are likely due to the same basic cloud chemistry as on Jupiter. However, because Saturn's clouds are thicker, there are fewer holes and gaps in the top layer, with the result that we rarely glimpse the more colorful levels below. Instead, we see only the topmost layer, which accounts for Saturn's less varied appearance. 2. In what ways are the observed characteristics of the major satellites of the Jovian planets similar to and different from one another? Europa's icy surface is only lightly cratered. Europa Liquid Water Locked in Ice Europa is covered by an ocean of liquid water whose surface layers are frozen. Ganymede has a weak magnetic field, about one percent that of Earth, suggesting that the moon's core may still be partly molten. If that is so, then Ganymede's heating and differentiation must have happened relatively recently. Saturn's largest moon Titan's atmosphere. it may contain rain, snow, and fog. Miranda displays a wide range of surface terrains, including ridges, valles, faults, and many other geological features. To explain why Miranda seems to combine so many types of terrain, some researches have hypothesized that is has been catastrophically disrupted several times, with the pieces falling back together in a chaotic, jumbled way. the density of the Galilean moons vary with increasing distance from Jupiter Their densities decrease with increasing distance from Jupiter in a manner very reminiscent of the falloff in density of the terrestrial planets with increasing distance from the Sun. 3. In what ways are the interior structures of the Jovian planets similar to and different from one another? Why do the interior structures differ? The blue color of the outer jovian planets is the result of their relatively high percentages of methane. The greater the concentration of methane, the bluer the reflected light. Therefore Uranus, having less methane, looks blue-green, while Neptune, having more methane, looks distinctly blue. Atmospheric Composition of Uranus and Neptune The atmospheres of Uranus and Neptune are very similar in composition to that of Jupiter-the most abundant gas is molecular hydrogen (84 percent), followed by helium (about 14 percent) and methane, which is more abundant on Neptune (about 3 percent) than on Uranus (2 percent). The abundance of hydrogen and helium on these worlds is itself a consequence of the strong jovian gravity. The jovian planets are massive enough to have retained even the lightest gas, hydrogen, and very little of their original stmospheres have escaped since the birth of the solar system 4.6 billion years ago. We do not expect the hydrogen and helium in the interiors of Uranus and Neptune to be compressed as much as in the two larger jovian worlds, yet the average densities of Uranus and Neptune are actually greater than the desity of Saturn, and similar to that of Jupiter. Neptune does have an internal source of heat-the planet emits 2.7 times more energy than it receives from the Sun. Uranus apparently has no internal energy source, radiating into space the same amount of energy as it receives from the Sun. It never experienced helium precipitation, and its initial supply of heat was lost to space long ago. 4. What are the magnetic field properties of each of the Jovian planets? Where do we think the magnetic fields come from? All four jovian worlds have strong magnetic fields and emit radiation at radio wavelengths. The combination of rapid overall rotation and an extensive region of highly conductive fluid in its interior gives Jupiter by far the strongest planetary magnetic field in the solar system. The planet's intrinsic field strength is some 20,000 times that of Earth. Jupiter is surrounded by a vast sea of energetic charged particles (mostly electrons and protons), somewhat similar to Earth's Van Allan belts but very much larger. We do not expect the hydrogen and helium in the interiors of Uranus and Neptune to be compressed as much as in the two larger jovian worlds, yet the average densities of Uranus and Neptune are actually greater than the desity of Saturn, and similar to that of Jupiter. Neptune does have an internal source of heat-the planet emits 2.7 times more energy than it receives from the Sun. Uranus apparently has no internal energy source, radiating into space the same amount of energy as it receives from the Sun. It never experienced helium precipitation, and its initial supply of heat was lost to space long ago. 5. How do the appearances of the ring systems of the Jovian planets differ from one another? Neptune is surrounded by four dark rings. Three are quite narrow, like the rings of Uranus, and one is quite broad and diffuse, more like Jupiter's ring. The outermost ring is noticeably clumped in places. The clumping is caused by shepherd satellites. 6. What is meant by shepherd and co-orbital satellites? It seems as though the ring's intricate structure, as well as its thinness, arises from the influence of two small moons, known as shepherd satellites, that orbit about 1000 km on either side of it. shepherd satellite Satellite whose gravitational effect on a ring helps preserve the ring's shape. Examples are two satellites of Saturn, Prometheus and Pandora, whose orbits lie on either side of the F ring. 7. Explain how astronomers are able to determine the interior structure of a Jovian planet. We do not expect the hydrogen and helium in the interiors of Uranus and Neptune to be compressed as much as in the two larger jovian worlds, yet the average densities of Uranus and Neptune are actually greater than the desity of Saturn, and similar to that of Jupiter. Neptune does have an internal source of heat-the planet emits 2.7 times more energy than it receives from the Sun. Uranus apparently has no internal energy source, radiating into space the same amount of energy as it receives from the Sun. It never experienced helium precipitation, and its initial supply of heat was lost to space long ago.. 8. Describe the methods used to discover Uranus, Neptune, and Pluto. In what years were each discovered? The British astronomer William Herschel discovered the planet Uranus in 1781. In 1930, the American astronomer Clyde Tombaugh, working with improved equipment and photographic techniques at the Lowell Observatory, finally succeeded in finding the ninth planet Pluto. 9. Describe the magnetic fields of the Jovian planets in comparison with that of Earth. Jupiter's magnetic field, this metallic Hydrogen is an excellent conductor of electricity. The energy that powers the reactions comes in many forms: the planet's own internal heat, solar ultraviolet radiation, aurorae in the planet's magnetosphere, and lightning discharges within the clouds. All four jovian worlds have strong magnetic fields and emit radiation at radio wavelengths. 10. Make a table of the characteristics of the major satellites of the Jovian planets as follows: Along the left edge place the satellite names; along the top, write craters, faults or cracks, mountains, valleys, scarps, atmosphere, volcanic activity, and density. Fill in the table with an X for each characteristic shown by each satellite. If the density is known place it in the density column. What general conclusions about groups of satellites and satellite systems can you make? Saturn's largest moon, Titan, makes it of particular interest to astronomers? Titan's atmosphere. it may contain rain, snow, and fog. Ganymede has a weak magnetic field, about one percent that of Earth, suggesting that the moon's core may still be partly molten. If that is so, then Ganymede's heating and differentiation must have happened relatively recently. Miranda displays a wide range of surface terrains, including ridges, valles, faults, and many other geological features. The gravitational influence of Saturn's innermost medium-sized moon, Mimas. Over time, particles orbiting within the Division have been deflected by Mima's gravity into eccentric orbits that cause them to collide with other ring particles, effectively moving them into new orbits at different radii. The net result is that the number of ring particles in the Cassini Division is greatly reduced. 11. In what ways is Pluto similar to and different from both the Jovian and the terrestrial planets? Pluto's average density of 2000 kg/m3 is too low for a terrestrial planet but far too high for a jovian one. Instead, the mass, radius, and density of Pluto are just what we expect for one of the icy moons of a jovian planet. Indeed, Pluto is comparable in both mass and radius to Neptune's large moon, Triton. APPLYING YOUR KNOWLEDGE 1. The Jovian planets can be described as objects that have changed little since their formation, while the terrestrial planets have changed a great deal. Explain the meaning of this statement and give examples of its validity. The Jovian planets are giant planets. The terrestrial planets are small planets. 2. What is the distance in kilometers from Dione to Dione B? From Tethys to its co-orbital satellites? (Note: You can answer this question without mathematics!) 3. What would you conclude about the formation of the solar system if Jupiter had the same composition as Earth? 4. Speculate on what the Voyager spacecraft might have found if it had gone on to Pluto? A small sized uninhibited dark planet. >5. Compute Saturn's density relative to Earth's, given its diameter of 9 Earth radii and 95 Earth masses. What is its density relative to that of water (1 gm/cm3)? >6. Saturn's Roche limit is located at 2.4 times the planet's radius. Measure the inner and outer radii of Saturn's rings from Figure 10-1, and express them in terms of Saturn's radius. Are these distances inside or outside the Roche limit? >7. Saturn's innermost ring begins at about 1-11Rs (Saturn radii), and the outermost one extends to about 6R. How much longer does it take an outer-ring particle to revolve around the planet relative to a particle at the inside of the innermost ring? >8. Why would you weigh nearly the same on Saturn as you do on Earth? Make the computation. >9. How far above Io's surface is the volcano in Figure 10-13b? What implicit assumption are you making in solving the problem? >10. Determine the size of the smallest feature you can see on the Earth-based photograph of Jupiter in Figure 10-1. >11. Compute the ratio satellite radius/planet radius for the largest satellite in each planetary system through- out the solar system. Which if any, stand out from the rest? Chapter 11 Page 255 The Properties of Light Light The study of light is important because the only way we can learn anything in astronomy is by analyzing the light that we receive. From light, we can determine how fast something is moving, its rotation, mass, composition, and age. We cannot say what light is, but we can describe how it behaves. Observed Properties of Light In the wave model, light is made up of a combination of electric and magnetic waves. The resulting electromagnetic wave produces the type of light we see. There are various types of electromagetic waves, which together form the electromagnetic spectrum of gamma rays, x-rays, ultraviolet, visible, infrared, and radio waves. All these different parts of the electromagnetic spectrum are all the same except for their wavelengths (the distance between successive peaks of a wave): gamma rays are the shortest, followed by x-rays, ultraviolet, visual, infrared, and radio, which is the longest. These all move at the same speed, which is the speed of light (denoted by c), equal to 186,000 miles per second or 300,000 kilometers per second. The frequency of a wave is the number of complete wave crests that pass a given point per second. There is an important relationship between wavelength, frequency, and the speed of light: f=c/ Obviously, from this equation we see that the shorter the wavelength, the higher the frequency, and vice versa. The wave model of light allows us to understand one other observed phenomenon: SUMMARY QUESTIONS 1. What is meant by reflection and refraction? Reflection Refraction Interference Diffraction Polarization So me really neat applications of some of the above to the Earth's atmosphere.Atmosphe ric optical effects Observed phenomena: Light is observed to be reflected from a surface. Light is observed to be refracted through a surface. Refraction is the bending of light as it passes from one medium to another air into water. These two observations can be understood through the ray model of light. In this model, we can think of light as a beam or ray of something. This model predicts that the angle of reflection equals the angle of incidence. It also predicts the details of how light is refracted between different media. The ray model does an exceptionally fine job of predicting the behavior of reflected and refracted rays of light. Refraction, the bending of light as it passes from one medium to another air into water also demonstrates this model. More observations of light phenomena: One beam of light that intersects (collides) with a similar beam of light will show interference. When light beams add, we have constructive interference, whereas when they subtract, we have destructive interference. A variety of demonstrations shown enable us to see this. In addition, light passing through a narrow slit, or past a barrier, does not travel in straight lines, is bent. The bending of light as it passes through a slit or past a barrier is called diffraction (NOT defraction!). Interference and diffraction cannot be understood in terms of the ray model of light. Instead, another model, called the wave model, is used. Wave model of light: accounts for interference and diffraction was well as reflection and refraction. it is a much more inclusive model than the ray model. In a Newtonian telescope another type of a reflecting telescope. The light is intercepted by a flat secondary mirror before it reaches the prime focus and deflected 90°, usually to an eyepiece at the side of the instrument. This is a popular design for smaller reflecting telescopes, such as those used by amateur astronomers. Each design of the four telescopes uses a primary mirror at the bottom of the telescope to capture radiation, which is then directed along different paths for analysis. reflecting telescope A telescope which uses a mirror to gather and focus light from a distant object. refracting telescope A telescope which uses a lens to gather and focus light from a distant object. refraction The tendency of a wave to bend as it passes from one transparent medium to another. 2. What is meant by diffraction? In what situations does it occur? How does diffraction vary with the wavelength of the light and the width of the aperture through which it travels? diffraction The tendency of waves to bend around corners. The diffraction of light establishes its nature as a wave. Because of diffraction, the angular resolution of radio telescopes is generally quite poor compared with that of their optical counterparts. 3. What is the meaning of wavelength and frequency? What is the relationship among wavelength, frequency, and speed of a wave? wavelength The length from one point on a wave to the point where it is repeated exactly in space, at a given time. frequency The number of wave crests passing any given point per unit of time. Here's an observation concerning light that cannot be understood in terms of the wave model: Photoelectric Effect If you have a metal with electrons on the surface, and light is incident on this surface, an observer will see electrons ejected from the surface. The ejected electrons produce an electric current. Experiments show that if yellow or red light is used, no current is produced; if blue or ultraviolet light is used, a current is produced. How can we understand this? Photon Model The photon model looks at light as consisting of bundles of energy-a beam made up of small particles, each of which have energy. (A photon is sometimes referred to as a quantum of light, too.) Since photons have energy, when they strike the surface of a metal, the photons can eject the electrons from the surface IF the incident photons have enough energy. The energy of a photon is given by: E = hf E = photon energy f = wave frequency h = Planck's constant From this equation, we see that photon energy is directly proportional to the wave frequency. The higher the frequency, the more energy the photon has. This equation is important because it connects the photon model with the wave model. Because frequency and wavelength are related via the velocity of light by c = f the equation can be rewritten in the following form: E = hc/. From this we see that the shorter the wavelength, the higher the photon energy. A wave with a short wavelength will have high frequency-->high energy A wave with a long wavelength will have a low frequency-->low energy Important note: The energy we are talking about is the energy that each and every photon has. This individual photon energy has nothing to do with how bright a source of radiation might be. The brightness of a radiation source is determined by the number of photons striking a detector each second. The more photons, the brighter the object. We could have bright source having low energy photons (lots of low energy photons), or a faint source having high energy photons (few high energy photon). 4. What do the words electromagnetic spectrum mean? electromagnetic spectrum The complete range of electromagnetic radiation, from radio waves to gamma rays, including the visible spectrum. All types of electromagnetic radiation are basically the same phenomenon, differing only by wavelength, and all move at the speed of light. 5. What is the importance of the concept of atmospheric windows for astronomy? Clear skies to be able to see better without clouds or light pollution. To be able to see stars brightly in the dark sky. 6. What is the meaning of interference? How does the concept explain the slit experiment in Figure 11-11? interference The ability of two or more waves to interact in such a way that they either reinforce or cancel each other. 7. What is meant by the polarization of light? Why is it important to astronomy? polarization The alignment of the electric fields of emitted photons, which are generally emitted with random orientations. Polarization We've just seen that we can think of light in terms of waves traveling toward the observer. If you were able to see the plane in which the wave is vibrating, at one moment the plane would be in one direction while the wave you see a moment later would be in another plane. Then another, etc. In other words, "normal" light has a random plane for its wave vibration. However, if you are able to force the light to vibrate in one plane, we say the light is polarized. This happens in nature. In fact, it happens within the Earth's atmosphere, from planetary surfaces and atmospheres, from certain stars and from certain galaxies. Understanding the polarization, therefore, provides useful informationon the properties of various types of astronomical objects. A variety of demonstrations were shown to help you understand polarization. There is an activity in your Activity Manual that you are to do and hand in. We see that the wave model allows us to understand all the observed properties of light. 8. What is meant by the wave-particle duality of both light and matter? electromagnetic radiation Another term for light, electromagnetic radiation transfers energy and information from one place to another, even through the vacuum of empty space. matter-dominated universe A universe in which the density of matter exceeds the density of radiation. The present-day universe is matter-dominated. 9. In what way does the energy of a photon depend on its wavelength? Arrange radiations of various types in order of increasing photon energy. photon Individual packet of electromagnetic energy that makes up electromagnetic radiation. APPLYING YOUR KNOWLEDGE 1. Summarize the models we use to understand light. What evidence is used to validate each model? 2. Explain the differences between the bending of light by refraction, and the bending by diffraction. Refraction, the bending of light as it passes from one medium to another (e.g. air into water) also demonstrates this model. More observations of light phenomena: One beam of light that intersects (collides) with a similar beam of light will show interference. When light beams add, we have constructive interference, whereas when they subtract, we have destructive interference. A variety of demonstrations shown enable us to see this. In addition, light passing through a narrow slit, or past a barrier, does not travel in straight lines, is bent. The bending of light as it passes through a slit or past a barrier is called diffraction (NOT defraction!). Interference and diffraction cannot be understood in terms of the ray model of light. Instead, another model, called the wave model, is used. 3. What is the importance of a photoelectric effect in providing evidence in favor of the photon description of light? The photoelectric effect showed that the ability to free an electron from an atom in a substance does not depend on the intensity of light. A certain amount of energy is required to remove the electron from its parent atom. If the photon energy is below the required energy, then the electron is not removed. This suggests that light can be thought of as a particle, or packet of energy, called a "photon." This is precisely the "quantum" nature of light. >4. Suppose your favorite radio station's frequency is 91.5 megahertz millions of cycles per second. What is the wavelength of the signal? Recall the relationship between wavelength and frequency: lambda = c/f = 3x10^(10)(cm/s)/91.5x10^(6)Hz = 328 cm = 3.28 m >5. How much more energy does a 1000 A photon have than one having a wavelength of 10,000 A? The energy of a photon, according to Planck, is given by E=hf, and the frequency is given by f=c/lambda, or E=hc/lambda. So E is inversely proportional to the wavelength, lambda. In this problem, the 1000 Angstrom photon clearly has more energy simply because it has a shorter wavelength. How much more energy does it carry than the 10,000 Angstrom photon? Simple, take a ratio: E(1000)/E(10000)=10000/1000 = 10. The short wavelength photon carries 10 times as much energy as the long wavelength photon. >6. What is the frequency and the energy of a photon having a wavelength of 21 cm? Here, we just apply the formula mentioned in question 5: f=c/lambda f=c/lambda = 3x10^(10)/21cm = 1.4x10^(9) Hz = 1400 MHz To get the energy, E=hf = 6.63x10^(-34) Js x 1.4x10^(9) Hz = 9.3x10^(-25) J Chapter 12 Page 275 SUMMARY QUESTIONS 1. How do both a pinhole camera and a lens form a real image of an object? Use a diagram in your explanation. 2. What effects do spherical and chromatic aberration have on an image? chromatic aberration The tendency for a lens to focus red and blue light differently, causing images to become blurred. 3. What are the basic parts of a telescope? What is the function of each part? Use diagrams in your answers. Objective Lens Eyepiece Focus Knob a long tube Viewfinder Fine-Adjustment Knobs Lock Levers lens mirror reflecting telescope A telescope which uses a mirror to gather and focus light from a distant object. refracting telescope A telescope which uses a lens to gather and focus light from a distant object. collecting area The total area of a telescope that is capable of capturing incoming radiation. The larger the telescope, the greater its collecting area, and the fainter the objects it can detect. 4. What is meant by resolving power as it applies to a telescope? Fortunately, radio astronomers can combine two or more radio telescopes to improve the resolving power. Such a linkup of radio telescopes is called a radio interferometer and has the resolving power of a radio telescope whose diameter equals the separation of the radio telescopes. For example the Very Large Array radio interferometer uses multiple radio dishes spread across the New Mexico-Arizona desert to simulate a single radio telescope with a diameter of 40 km. 25 miles. It can produce radio maps with a resolution better than 1 second of arc. 5. How does seeing affect the image produced by a telescope? How does the effect of seeing compare with the effects of diffraction? seeing A term used to describe the ease with which good telescopic observations can be made from Earth's surface, given the blurring effects of atmospheric turbulence. diffraction The tendency of waves to bend around corners. The diffraction of light establishes its nature as a wave. Because of diffraction, the angular resolution of radio telescopes is generally quite poor compared with that of their optical counterparts. 6. What is the principal advantage that telescopes of large diameter have over those with small diameter? Radio telescopes are built large in part because cosmic radio sources are extremely faint. 7. What are the advantages and disadvantages of each of the principal types of reflecting telescopes? reflecting telescope A telescope which uses a mirror to gather and focus light from a distant object. Reflecting telescopes use a concave mir- ror. The advantages of the reflecting tele- scope have made it the preferred design for modern observatories. 8. What are the advantages and disadvantages of radio telescopes as compared with optical telescopes? Radio telescopes It also depends on the wavelength of the radiation. A very long wavelengths, like those of radio waves, im- ages become fuzzy because of the large diffraction fringes. As with an optical telescope the only way to improve the resolving power is to build a bigger tele- scope. Consequently radio telescopes must be quite large. Because there are two ways to focus light, there are two kinds of astronomical telescopes. Refracting telescopes use a large lens to gather and focus the light. Radio telescopes are built large in part because cosmic radio sources are extremely faint. Cosmic objects across the sky Can see and study a astronomical object like a Radio Galaxy. Visible image of the radio galaxy Centaurus A, with the radio emission from the region superimposed (in false color, with red indicating greatest radio intensity, blue the least). The resolution of the optical image is about 1", that of the radio map is 12". The angular resolution of ground-based optical telescopes is more seriously limited by Earth's turbulent atmosphere than by diffraction. Radio astronomers can sometimes overcome the problem of poor angular resolution by using a technique known as interferometry. This technique makes it possible to produce radio images of much higher angular resolution than can be achieved with even the best optical telescopes on Earth or in space. Optical Telescopes Astronomers build optical telescopes to gather light and focus it into sharp images. This requires sophisti- cated optical and mechanical designs, and it leads astronomers to build gigantic telescopes on the tops of high mountains. Radio Telescopes in deep valleys detect weak radio sources. APPLYING YOUR KNOWLEDGE 1. What are the pros and cons of placing an optical observatory on the roof of a university building? astronomers to build gigantic telescopes on the tops of high mountains. The angular resolution of ground-based optical telescopes is more seriously limited by Earth's turbulent atmosphere than by diffraction. Atmospheric Blurring. Optical telescopes on Earth can see angular detail down to about 1" or few arc second. Optical astronomers can observe only at night. 2. Why do astronomers need large telescopes on Earth? In Space? Why is the word large important? Astronomers always want to maximize the amount of data/information for an object by collecting and detecting as many photons as possible from the source. This is achieved by making their telescopes as large as possible. Why? (1) Image brightness (i.e. number of photons) is directly proportional to the collecting area of the telescope. (2) Resolution, or clarity of the image, is inversely proportional to the collecting area. Note that telescopes on Earth suffer from blurring effects caused by turbulence in Earth's atmosphere. To a certain extent, these effects can be minimized (but not eliminated completely) by a technique known as adaptive optics. However, a telescope placed in space (i.e., above Earth's atmosphere) is free from these blurring effects. One example is the successful Hubble Space Telescope. 3. Why are radio telescopes so much larger than optical telescopes? Recall that the resolving power (or resolution) of a telescope is proportional to the wavelength of the incoming electromagnetic radiation and inversely proportional to the diameter of the telescope's collecting area (i.e., objective). Since the wavelength of radio waves is very long (on the order of cm), compared to visible light for example, it is very difficult to achieve a small resolving power with a radio telescope unless you make it HUGE! Radio telescopes are large in part to improve their angular resolution, which is poor because of the long wavelengths at which they observe. Radio telescopes are large in part because the sources of radio radiation they observe are very faint. Optical telescopes on Earth can see angular detail down to about 1" or few arc second. 4. Why must the shape of the mirror of an optical telescope be more accurate than the shape of the antenna of a radio telescope? 5. Given the choice of a reflecting telescope at the prime focus, Cassegrain focus, or coude focus, which would you choose to use to photograph a faint galaxy? >6. Giovanni Schiaparelli, who claimed to observe canali later translated as canals on Mars, used a telescope having a 22-cm-diameter objective. What is the resolving power of such a telescope? What would the true size of Martian canals have to be for Schiaparelli to have observed them? Assume Mars is 0.5 AU from Earth at the time of observation. >7. An 8-inch amateur telescope with a focal length of 2000 mm produces an image of the moon 1.7 cm in diameter. How large an image of the Moon does the 200-inch telescope focal length = 16.7 meters produce? What would be the image size for a 50-inch telescope having the same focal length as the 200-inch telescope? >8. Suppose you want the Moon to appear 45 across when viewed through a telescope of 125-cm focal length. What focal length eyepiece must you use? >9. Compare the theoretical light-gathering and resolving powers of telescopes having the following objective diameters to a telescope having a 2.5 cm 1-inch. objective: 20-cm 8-inch, 127-cm 50-inch, 2.54-m 100 inch, 5.08-m 200inch, 10-m 400-inch. Diameter Light-Gathering Power Resolving Power 8-inch 64x 8x 50-inch 2500x 50x 100-inch 10000x 100x 200-inch 40000x 200x 400-inch 160000x 400x The table is interpreted as follows: The 8-inch telescope gathers 64 times as much light as the 1-inch and has a resolving power 8 times smaller than the 1-inch. >10. Compare the resolving power of one 10-m Keck telescope with what will be possible along with the Keck-2 telescope 85 meters away, when the com- bination is used for interferometry at a wavelength of 2 microns 1 micron = 0.0001 cm. >11 The European Southern Observatory's VLT will consist of four separate telescopes, each having 8-meter diameter mirrors. How large would a single mirror have to be to have the same light-gathering power? How much more light than the human eye will it collect. Chapter 13 Page 296 SUMMARY QUESTIONS 1. What are the three principal types of spectra? Explain the conditions under which each is produced. The three types of spectra emission, absorption, and continuous. 2. What effect does temperature have on the color and energy distribution of the radiation emitted by a hot object? cold temperature hot temperature 3. How can you describe the formation of the absorption spectrum of the Sun in terms of a simple solar model? Standard Solar Model A self-consistent picture of the Sun, developed by incorporating the important physical processes that are believed to be important in determining the Sun's internal structure, into a computer program. The results of the program are then compared with observations of the Sun, and modifications are made to the model. The Standard Solar Model, which enjoys widespread acceptance, is the result of this process. 4. How do the interactions between photons and atoms produce emission and absorption spectra? cosmological Redshift As the universe expands, photons of radiation are stretched in wavelength, giving rise to the cosmological redshift. Although dark matter does not interact directly with photons, the background radiation is influenced slightly by the gravity of the growing dark clumps. excited atoms absorb and reemit radiation at characteristic frequencies the absorption of a more energetic (higher-frequency, shorter-wavelength) ultraviolet photon, this one having a wavelength of 102.6 nm (1026 A), causing the atom to jump to the second excited state. From that state, the electron may return to the ground state via either one of two alternate paths. 1. It can proceed directly back to the ground state, in the process emitting an ultraviolet 102.6 nm photon identical to the one that excited the atom in the first place. 2. Alternativel, it can cascade down one orbital at a time, emitting two photons: one having an energy equal to the difference between the second and first excited states, and the other having an energy equal to the difference between the first excited state and the ground state. Because electrons may exist only in orbitals having specific energies, atoms can absorb only specific amounts of energy as their electrons are boosted into excited states. atoms can emit only specific amounts of energy as their electrons fall back to lower energy states. 5. What is represented in an energy-level diagram? Draw the energy-level diagram for a hydrogen atom, and indicate the principal transitions. hydrogen atoms, radiate naturally at a wavelength of 21 cm. excited hydrogen atom when an electron in the ground state of a hydrogen atom flips its spin to become parallel to the spin of the proton in the nucleus. 6. Why do different chemical elements have different characteristic spectral lines? Different chemicals interreact differently with each other. Hydrogen gas is a chemical element and can be in hot temperatures. 7. What are Kirchhoff's laws for dark-line and bright-line spectra? How does atomic theory explain the Sun's flash spectrum? Kirchhoff's laws Three rules governing the formation of different types of spectra. 8. How can you use the spectra of nebulae to show that some are composed of stars and others are composed of hot gases? 9. How is the spectrum of an emission nebula formed? The light produced by an emission nebula is the result of atomic transitions from the hydrogen gas in the nebula. The hot star ionizes the surrounding nebula and emission lines are produced as the electrons, when recaptured, make transitions from higher levels to lower levels. The light we receive at visible wavelengths is the result of hydrogen Balmer emissions. The strongest emission is from the Balmer alpha transition at 656.3 nm, which is dark red in color. Other wavelengths are present and cause the color to be softened to a light red from the dark red of hydrogen-alpha. By contrast a reflection nebula contains very little gas and a large amount of dust and all of the visible light we receive from it is reflected and scattered light, none of it comes from atomic transitions in the nebula itself. Consequently, the spectrum we see from a reflection nebula shows absorption lines identical to those of the nearby star. The nebula will also appear blue in color because small dust particles preferentially scatter blue light much more efficiently than they scatter longer wavelength (red) light. 4. Star formation occurs in regions that contain a large amount of dust which both obscures visible and shorter wavelength light and produces large amounts of infrared light. Additionally, protostars are not generally very hot and produce most of their energy at infrared wavelengths. 5. That star formation is a continuing process is seen in the existence of hot, blue main sequence stars. These stars have lifetimes of a few million years. Yet our sun is 4.5 billion years old. If star formation were not a continuing process, the hot main sequence stars would no longer exist. Additionally, we see T Tauri stars which are above and to the right of the main sequence in the H-R diagram and associated with gas and dust clouds and found in very young star clusters. This also supports the ongoing formation of new stars. 6. Herbig-Haro object appear to be formed where the hot high velocity jets from a bipolar flow from a T Tauri star run into the interstellar medium. APPLYING YOUR KNOWLEDGE 1. Consider the following experiment. A clear glass tube filled with sodium gas has light from an electric sodium lamp focused into it. A sodium lamp is yel- low in color. The inside of the tube is observed to contain a cone of yellow light in the region in which the sodium lamp is focused. However, when the electric sodium lamp is replaced with an electric lamp filled with mercury gas, no cone of light is observed from inside the tube. Explain the experiment. Recall the demonstrations we did in class with the gas discharge tubes. Each element has its own set of spectral lines, like a fingerprint, that are produced by the allowed electron transitions in the atom. Mercury will therefore have a series of spectral lines different than that of sodium because it has a different atomic number. The cone of light is visible from the when the sodium lamp is used because the light is composed of photons of the exact energies required for transitions. However, when the light from the Mercury gas is shown onto the sodium gas, no light cone of light is observed because the sodium gas can only absorb light at the wavelengths described by the spectrum of sodium. 2. List all possible downward transitions an electron in the sixth energy level in the hydrogen atom can make. List their wavelengths when known. Electrons can also go from outer orbits to inner orbits. As electrons move closer to the nucleus, they give off energy that appears as photons. Once again, the amount of energy can be determined using E=hf=hc/. An emission spectrum will be observed when an electron goes from an outer state to an inner state. The energy required to move an electron from the first excited to the second excited state is not as great as the energy required to move the electron from ground state to the first excited state. This is because the electron is not held as tightly to the nucleus as when it was in ground state, so less energy is required to make a transition. The energy level diagram shows the energy required to move from one orbit to another. As you move further out, the levels get closer together because they involve smaller amounts of energy. The amount of energy given off as the electron drops from the fifth to the first levels equals the length of the line shown on the energy level diagram, and corresponds to the wavelength since E=hf=hc/. If a photon drops from the fifth level to the second level, the electron will not lose as much energy and will have a longer wavelength than the photon which moved from the fifth level to the first. Similarly, a photon which moves from the fifth level to the third will have yet less energy than the other two and will have a longer wavelength. 3. Why does the Lyman series occur at shorter wave- lengths than the Balmer series? The Lyman transitions are to and from the n=1 state, i.e. the ground state. This state has the lowest energy because the electron likes to be close to the positively charged nucleus (in this case, a proton). The Balmer transitions are to and from the n=2 state (the first excited state). To move an electron to a higher energy state it takes more energy to move the electron out of the n=1 state than the n=2 state. This makes sense because the electrostatic force of attraction between the electron and the proton nucleus is strongest in the n=1 state (i.e. you must do more work against this force to promote the electron to a higher energy level). Since the Lyman transitions require more energy, then the wavelengths will be shorter (recall that photon energy and wavelength are inversely related. All the transitions that go down to the ground state are known as the Lyman series. They occur in the ultraviolet region. The transitions that involve the first excited state are the Balmer series. These occur in the visual part of the spectrum. 4. Given that most of the hydrogen atoms in the Sun's photosphere are in their lowest energy state, what spectral series of hydrogen would be produced most strongly in the Sun? If most H atoms are in the ground state (n=1), then the only possible transitions for these atoms are the Lyman series (i.e., 1 to 2, 1 to 3, etc.). So we would expect to see the Lyman lines in the spectrum (remember: these lines are not in the visible part of the EM spectrum, rather the UV). 5. Suppose you observed the spectrum of some astro- nomical object and found it to have both absorption and emission lines. What might be a reasonable explanation for the nature of the object? There are three types of spectra: 1) continuous spectrum 2) dark line spectrum 3) bright line spectrum 1) A luminous solid or liquid, or a gas at a high pressure, emits light at all wavelengths-->produces a continuous spectrum 2) A luminous rarefied (low density) gas emits light whose spectrum shows a bright line spectrum-->produces an emission line spectrum 3) White light from a luminous source, when passed through a cooler gas, may be absorbed at certain wavelengths, giving a dark line spectrum or absorption line spectrum 6. If you are star-gazing on a clear night and notice two stars, one of which appears bluish and the other reddish, what could you conclude about the relative characteristics of the two stars? The blue star is obviously emitting more blue photons than the red star. According to the thermal radiation laws, the blue star's Planck spectrum will peak at shorter wavelengths, i.e. a shorter wavelength of maximum intensity, it will have a higher temperature. The blue star is hotter. >7. What is the wavelength of the strongest emission of energy for a body of temperature 3 K? As you will see later in the book this temperature is the current temperature of radiation still around from shortly after the universe began! Apply Wein's Law to calculate the wavelength of maximum intensity. wavelength(max) = (3x10^7)/3 = 10^7 Angstroms. This is in the microwave/radio region of the EM spectrum, beyond the infrared band. >8. What are the frequency and the energy of a photon having a wavelength of 21 cm? >9. Relative to the Sun, how much more energy per unit area does a star with a temperature of 22,000 K radiate? Just apply the Stefan-Boltzmann Law and take a ratio of the energy emitted by the star to the energy emitted by the Sun. The Sun's temperature is about 6000 K, so we have: E(star)/E(sun) = (22000/6000)^4 = (3.67)^4 = 181 >10. Relative to the Sun, how much more energy per second comes from the entire surface of a star that has a radius one-third that of the Sun and a tem- perature of 22,000 K? Hint: Remember that the energy per second per unit area depends on 7 4. >11. Consider the following logarithmic scale: 3 15 ? 375 What number should be in the place of the question mark? Explain your reasoning. >12. Compute the temperature of a star that appears to be red. Do the same for a star that appears to be blue. Chapter 14 Page 319 SUMMARY QUESTIONS 1. What are the standard spectral types in order from hottest to coolest? What are the main characteristics of each class temperature range, color, prominent spectral features? The large, cool stars found at the upper right of the H-R diagram are red dwarf. red dwarf Small, cool faint star at the lower-right end of the main sequence on the Hertzsprung-Russell diagram. red giant A giant star whose surface temperature is relatively low, so that it glows with a red color. red supergiant An extremely luminous red star. Often found on the asymptotic giant branch of the H-R diagram. The small, hot stars found at the lower left of the H-R diagram are white dwarf. white dwarf A dwarf star with a surface temperature that is hot, so that the object glows white. Going from spectral type O to M along the main sequence, stellar masses luminosity. 2. Why do the principal features of spectra change from one star to another? from top left (high-temperature, high-luminosity) to bottom right (low-temperature, low-luminosity). In other words, cool stars tend to be faint (less luminous) and hot stars tend to be bright (more luminous). This band of stars spanning the H-R diagram is known as the main sequence. 3. Why does relative motion between a source and an observer result in a change in the observed wavelength of emitted light? There is obviously relative motion between the Earth and the sky - one night of observation will determine that. Seeing the planets move around the Earth (apparently) and the Sun and the stars do the same thing through the year, it's a somewhat obvious choice to place the Earth at the center of the Solar system (= universe 2,000 years ago). The main argument against placing the Sun in the center (favored by Aristarchus) was the lack of measurable parallax for the stars. In other words, if the Earth is moving around the Sun, why don't we see some stars shift their positions relative to more distant stars through the year? The answer is that the stars are so incredibly far away (compared to the size of the Earth's orbit) that this motion is very hard to observe and less than 1 arc-second per year even for the closest stars. 4. What are three effects that alter the observed profile of a spectral line? Explain why each one changes the line profile. Bohr model First theory of the hydrogen atom to explain the observed spectral lines. This model rests on three ideas: that there is a state of lowest energy for the electron, that there is a maximum energy, beyond which the electron is no longer bound to the nucleus, and that within these two energies the electron can only exist in certain energy levels. APPLYING YOUR KNOWLEDGE 1. When lines of ionized helium are present in a spec- trum, will the lines of neutral helium have the same or different strength when compared to a spectrum in which no ionized helium lines are present? Explain. 2. In what energy state must a hydrogen atom be for it to absorb light at a wavelength of 4861 A? Describe how the atom might get to such an energy state. Examine the energy level diagram for Hydrogen in Figure 3-19. The wavelength 4861 Angstroms corresponds to one of the Balmer transitions, H-beta. The transition is between the n=4 and the n=2 state. The H atom must be in the n=2 state in order for it to absorb a 4861 Angstrom photon. To reach the n=4 state, the atom can either absorb a 4861 Angstrom photon or absorb energy due to a collision with another atom. Note that the energy transfered in the collision must be the equivalent energy of a 4861 Angstrom photon, otherwise the excitation will not occur. Excited energy state. 3. What will happen to a photon of wavelength 1220 A when it encounters a hydrogen atom? The atom is undisturbed by the photon, because 1220 Angstroms does not correspond to any transition in Hydrogen. 4. Stars known as white dwarfs studied in Chapter 18 have very high densities. How do you think spectral lines of a white dwarf might differ from that of a normal less dense star? If the density is very high, recall that the spectral lines will be broadened due to collisional broadening. The energy levels are slightly perturbed by ions that pass near by the atoms. The lines will appear "stronger." The inside of a neutron star would have to be much denser than the inside of a white dwarf. A neutron star is a star of a little over 1 solar mass com- pressed to a radius of about 10 km. Its density is so high that the matter is stable only as a fluid of neu- trons. 5. Consider a star with an expanding shell of hydrogen surrounding it. Make a drawing of the system, and then describe and draw the resulting spectrum by considering the radiation coming from the system's various parts. supernova remnant, the expanding shell of gas produced by the explosion of a star in 1572. The radio contour map has been color-coded to show intensity. Red is the strongest radio intensity and violet the weakest. 6. It has been found that the lines of hydrogen in the spectra of galaxies tend to be observed at longer and longer wavelengths the farther the galaxy is from us. Interpret this observation in terms of what you have learned. Since the lines are observed at longer wavelengths, this means they are redshifted. According to the Doppler effect, the galaxies are moving away from us, i.e. receding. Recall that the larger the shift in wavelength, the faster the source is moving in this case, the farthest galaxies are receding more quickly. The amount of energy a photon carries depends inversely on its wavelength. That is, shorter-wavelength photons carry more energy, and longer-wavelength photons carry less energy. Neptune's at- mosphere must pass through hydrogen gas that contains a small amount of methane, which is a good absorber of longer wavelengths. As a result red photons are more likely to be absorbed than blue photons, and that makes the light bluer. The spectrum of the Seyfert galaxy nuclei contains broad emission lines of highly ionized atoms. Emission lines suggest a hot low-density gas, and ionized atoms suggest that the gas is very excited. The closer the star is the hotter the star appears. The farther away the star is the colder the star appears or less faintly seen. >7. How rapidly would an object have to be moving for its color to change from blue (4000 A) to red (7000 A) because of the Doppler effect? What (incorrect!) assumption are you implicitly making? its color to change from blue (4000 A) to red (7000 A) >8. What would be the maximum contribution in angstroms of the Earth's orbital motion to the shift of a stellar absorption line? Assume a rest wave- length of 4000 A, and that the Earth travels at some 30 km/sec around the Sun. What would be the maximum contribution from the Earth's rotational motion, which is 0.46 km/sec at the equator? >9. At what wavelengths will the D lines of sodium at a rest wavelength of about 5900 A be observed in the spectrum of a star that is moving away from us at 90 km/sec? If it is moving toward us at 150 km/sec? >10. What would be the approximate spectral type of a star whose wavelength of maximum intensity was (a) 10 -5 cm, and (b) 1.2 X 10 -4 cm? Remember that spectral type is an indication of the star's effective (or "surface") temperature. We are given lambda_max, so we can apply Wein's Law to calculate the temperature of this star: Temperature = 3x10^(7) / lambda_max Let's convert lambda_max = 10^(-5) cm to Angstroms first: 10^(-5) cm x (1 Angstrom / 10^(-8) cm) = 10^(3) Angstroms, Temperature = 3x10^(7)/1000 = 30000 Kelvin This is an O Type star. For lambda_max = 1.2x10^(-4) cm, we have: Temperature = 3x10^(7)/12000 = 2500 Kelvin This is an M Type star. >11. A galaxy is observed to have two prominent lines in its spectrum at wavelengths of 5104 and 6891 A. Assuming these are redshifted Balmer lines, what is the speed of the galaxy relative to the Earth? Hint: If you have identified the lines correctly, you should get the same speed regardless of which line you see. Chapter 15 Page 340 SUMMARY QUESTIONS 1. Sketch and label the Hertzsprung-Russell diagram for all stars and identify each of the various groups of stars on it. Explain the terminology main sequence, red dwarf, white dwarf, giant, and supergiant. main sequence Well-defined band on the Hertzsprung& Russell diagram, on which most stars are found, running from the top left of the diagram to the bottom right. red dwarf Small, cool faint star at the lower-right end of the main sequence on the Hertzsprung-Russell diagram. white dwarf A dwarf star with a surface temperature that is hot, so that the object glows white. giant A star with a radius between 10 and 100 times that of the Sun. supergiant A star with a radius between 100 and 1000 times that of the Sun. 2. Why is the Hertzsprung-Russell diagram for the nearest stars different from that for the brightest stars in the sky? H-R Diagram of Prominent Stars A plot of luminosity against surface temperature (or spectral class), known as an H-R diagram, is a useful way to compare stars. Plotted here are the data for some stars mentioned earlier in the text. The Sun, of course, has a luminosity of one solar unit. Its temperature, read off the bottom scale, is 5800 K-a G-type star. Similarly, the B-type star Rigel, at top left, has a temperature of about 15,000 K and a luminosity more than 10,000 times that of the Sun. The M-type star Proxima Centauri, at bottom right, has a temperature of less than 3000 K and a luminosity less than 1/10,000 that of the Sun. 3. Why are a star's radius, temperature, and luminosity interrelated? mass-luminosity relation The dependence of the luminosity of a main-sequence star on its mass. The luminosity increases roughly as the mass raised to the third power. mass-radius relation The dependence of the radius of a main sequence star on its mass. The radius rises roughly in proportion to the mass. 4. How do the various groups of stars on the Hertzsprung-Russell diagram differ in terms of their radii? white dwarf A dwarf star with a surface temperature that is hot, so that the object glows white. white dwarf region The bottom left-hand corner of the Hertzsprung-Russell diagram, where white dwarf stars are found. red dwarf Small, cool faint star at the lower-right end of the main sequence on the Hertzsprung-Russell diagram. 5. Where on the main sequence do stars of different masses lie? Draw a schematic H-R diagram and indicate such locations. main sequence Well-defined band on the Hertzsprung& Russell diagram, on which most stars are found, running from the top left of the diagram to the bottom right. 6. What is the range of orders of magnitude for stellar mass, luminosity, radius, surface temperature, and density? luminosity One of the basic properties used to characterize stars, luminosity is defined as the total energy radiated by a star each second, at all wavelengths. luminosity class A classification scheme which groups stars according to the width of their spectral lines. For a group of stars with the same temperature, luminosity class differentiates between supergiants, giants, main-sequence stars, and subdwarfs. density A measure of the compactness of the matter within an object, computed by dividing the mass by the volume of the object. Units are kilograms per cubic meter (kg/m3), or grams per cubic centimeter (g/cm3). 7. What is the method of spectroscopic parallax? What are its advantages and disadvantages? spectroscopic parallax Method of determining the distance to a star by measuring its temperature and then determining its absolute brightness by comparing with a standard H-R diagram. The absolute and apparent brightnesses of the star give the star's distance from Earth. 8. What are the three main types of binary star systems? Describe them? binary-star system A system which consists of two stars in orbit about their common center of mass, held together by their mutual gravitational attraction. Most stars are found in binary-star systems. 9. How can astronomers determine the masses and radii of stars directly? Describe two techniques for measuring the mass of a galaxy. Astronomers can calculate the masses of some spiral galaxies by determining their rotation curves, which plot rotation speed versus distance from the galactic center. The mass within any given radius then follows directly from Newton’s laws. (Sec. 14.5) Rotation curves for a few nearby spirals are shown in Figure 15.18. We can use another statistical technique to derive the combined mass of all the galaxies within a galaxy cluster. As depicted in Figure 15.19(b), each galaxy within a cluster moves relative to all other cluster members, and we can estimate the cluster’s mass simply by asking how massive it must be in order to bind its galaxies gravitationally. Typical cluster masses obtained in this way lie in the range of 1013-1014 solar masses. Notice that this calculation gives us no information whatsoever about the masses of individual galaxies. It tells us only about the total mass of the entire cluster. Stellar Masses More than any other stellar property, mass determines a star's position on the main sequence. Low-mass stars are cool and faint, they lie at the bottom of the main sequence. Very massive stars are hot and bright; they lie at the top of the main sequence. The symbol "M" means "solar mass." How are distances determined using spectroscopic parallax? spectroscopic parallax Method of determining the distance to a star by measuring its temperature and then determining its absolute brightness by comparing with a standard H-R diagram. The absolute and apparent brightnesses of the star give the star's distance from Earth. If the distance to a visual binary is known, then the orbits of each component can be individually tracked, and the masses of the component can be determined. By studying the variation of the light from an eclipsing binary system-called the binary’s light curve-we can derive detailed information not only about the stars’ orbits and masses but also about their radii. As with all other objects, we measure a star’s mass by observing its gravitational influence on some nearby body-another star, perhaps, or a planet. If we know the distance between the two bodies, then we can use Newton’s laws to calculate their masses. APPLYING YOUR KNOWLEDGE 1. Suppose you have an eclipsing system in which the stars have the same diameter. Assuming the eclipses are central-that is, during the eclipses, the centers of the stars coincide-draw the resulting light curve. 2. Discuss the process by which astronomers determine a spectroscopic parallax. In your discussion be sure to specify what is observed and what is inferred. A direct way of measuring the distance to a star is by measuring its parallax angle. For distances of 100 pc or more the parallax angle is too small to measure (question: what is the corresponding parallax angle for a distance of 100 pc?). Astronomers therefore use spectroscopic parallax to determine the luminosity of the star by using the HR diagram. Once the luminosity and apparent brightness are know the distance is easily found by applying the inverse square law. But what do we need to observe in order to place a star on the HR Diagram? The observed quantity is the spectrum, and the temperature. From this and a study of spectral line widths the luminosity class of the star can be inferred on the HR diagram. spectroscopic parallax Method of determining the distance to a star by measuring its temperature and then determining its absolute brightness by comparing with a standard H-R diagram. The absolute and apparent brightnesses of the star give the star's distance from Earth. 3. Make up a table that shows the maximum and minimum observed values for the following proper- ties of stars; temperature, mass, diameter, density, and luminosity. Express your results both in absolute numbers and in terms of the Sun's value. Property Maximum Minimum Temperature (K) >100,000 1500 Mass (solar masses) 60-100 0.08 Diameter (solar radii) 1000 <0.01 Density (gm/cm^3) >10^6 <1(?) Luminosity (solar lum.) 10^6 10^(-3) temperature, solar surface has a temperature of 5800 K temperature: 5800 K (surface) 15,600,000 K (core) mass 1.989e30 kg diameter 1,390,000 km. Apparent angular diameter: 00°32'31" density luminosity 4. Rewrite the formula relating distance in parsecs and the parallax angle to be valid for astronauts observing from an orbit whose average distance from the Sun is A astronomical units. >5. What would be the distance to a star identical to the Sun whose apparent brightness is 10 16 times less than that of the Sun? If the star is identical to the Sun then the luminosity of the star is 1 solar luminosity. The star appears 10^16 times less than the Sun, therefore the ratio of their brightness is simply: B(Sun)/B(star) = 10^16 But we also know that the ratio of their brightness is given by the inverse square law as: B(Sun)/B(star) = (d(star)/d(Sun))^2 = 10^16 we have d(star)/d(Sun) = 10^8 or simply, d(star) = 10^8 d(Sun) = 10^8 A.U. Earth-Sun distance as a stan- dard measuring stick. In familiar units this distance is 93,000,000 miles (or 150,000,000 km1 Earth You are here! 0.983762 astronomical units from the Sun. The mass of a star determines its luminosity. The massive stars are very luminous and lie along the upper main sequence. The less massive stars are fainter and lie lower on the main sequence. >6. What would be the approximate period of revolu- tion for a binary system composed of two stars like the Sun for which the semi-major axis is (a) 1 AU, (b) 10 AU, and (c) 40 AU? Recall that Kepler's 3rd Law states: P^2(M1+M2)=A^3. Here, M1 + M2 = 2 solar masses. Kepler's 3rd Law can be written: 2P^2 = A^3. (a.) A=1 A.U. Just substitute in the numbers: 2P^2 = 1, or P^2 = 0.5 P = SQRT(0.5) = 0.71 years (b.) A=10 A.U. Gives 2P^2 = 10^3, or P = 22.4 years (c.) A=40 A.U. Gives 2P^2 = (40)^3 = 64000, or P = 179 years >7. To explain a possible period of 26 million years in the extinction of some biological species, scientists have suggested that the Sun might have a companion whose period is the interval between extinctions. What would be the distance to such a star which is known as Nemesis? How does this distance compare with the distance to the nearest star? >8. The star a Canis Majoris Sirius is a binary of period 50 years. Its semimajor axis is 7.5 seconds of arc, and the system's parallax is 0.378 second of arc. What is the sum of the masses of the two stars in solar mass units? 0.378 + 7.8 =0.456 >9. What is the distance to a blue supergiant star whose apparent brightness is 10 14 times less than the Sun's brightness, assuming a true luminosity of 10 4 the luminosity of the Sun? As seen in the H-R diagram in Figure 15-10, such supergiants do not all have the same luminosity. If the true luminosity is actually 2 X 10 4 that of the Sun, what is the star's distance? Com- pare the two distance estimates, and discuss how un- certainties in the inferred luminosity produce uncer- tainties in the derived distance. Hint: Appendix A10 may be helpful. Sun luminosity is 1 and apparent magnitude is -26.7. Spectral Type G2 V Polaris and Antares are at 10 4 as shown in Figure 15-10 A more detailed Hertzsprung-Russell diagram. Polaris appears to be Spectral type GO Antares is MO or OO. >10. How many times less massive is Jupiter than the least massive star shown in the mass-luminosity relation in Figure 15-20? >11. What would be the luminosity of a star whose temperature was 3000K and 1000 times the size of the Sun? The lumninosity of a star is proportional to the product of the square of the radius and the temperature to the fourth power: L prop. to R^2 T^4 Now we know the star has a temp, T=1/2 the temperature of the Sun, and we know R=1000 solar radii. Applying the above relation gives the luminosity of the star in units of solar luminosities: L = (1000)^2 x (1/2)^4 L(sun) L = 62,500 L(Sun) The luminosity would be very weak and a colder star. Spectral Classes Spectral Class Approximate temperature K Hydrogen Balmer Lines Other Spectral Features O 40,000 Weak Ionize helium B 20,000 Medium Neutral helium A 10,000 Strong Ionized calcium weak F 7500 Medium Ionized calcium weak G 5500 Weak Ionized calcium medium K 4500 Very weak Ionized calcium strong M 3000 Very weak Titanium oxide strong Chapter 16 Page 365 SUMMARY QUESTIONS 1. What is meant by Kelvin-Helmholtz contraction? What is its significance insofar as providing the Sun's energy? 2. What do we mean by nuclear fission and by nuclear fusion? Why is nuclear fusion a viable source for the Sun's power, while fission is not? nuclear fusion Mechanism of energy generation in the core of the Sun, in which light nuclei are combined, or fused, into heavier ones, releasing energy in the process. 3. What are the steps involved in the proton-proton chain? What is the net result in terms of what goes in and what comes out? proton-proton chain The chain of fusion reactions, leading from hydrogen to helium, that powers most main-sequence stars. 4. What are the general features of the CNO cycle? What is the end result in terms of particles going into the reaction and those coming out? The proton-proton chain and CNO cycle are both thermonuclear fusion reactions that convert four hydrogen nuclei to one helium nucleus with the release of energy. Both also occur in the cores of main sequence stars. The two differ in the manner in which the fusion reaction occurs, the temperature at which the reaction occurs, and the mass of the stars where each of these reactions dominate the energy production. The proton-proton chain requires a minimum temperature of 10 million K and involves only nuclei of hydrogen and helium. The proton-proton chain is the dominant reaction in main sequence stars with masses less than about 1.1 solar masses. The CNO cycle requires a minimum temperature of about 16 million K and involves hydrogen, carbon, nitrogen, and oxygen nuclei in the production of energy and the helium nuclei. The CNO cycle is the dominant source of energy for stars on the main sequence with masses greater than about 1.1 solar masses. The CNO cycle requires a greater temperature than the proton-proton chain because the Coulomb barrier is greater in the CNO cycle. The Coulomb force is determined by the charge on the particles that are trying to collide. The greater the charge, the greater the Coulomb barrier that must be overcome. In the proton-proton chain the largest number of positive charges that must be combined is four when the two 3He nuclei are combined. By contrast the reaction in the CNO cycle with the least number of charged particles that need to be combined is seven when the 1 H nucleus is combined with the 12 C nucleus. 5. What are the conditions of density and temperature required for fusion to take place? Why is each variable important? What would happen to the total amount of energy if the variables were altered? density A measure of the compactness of the matter within an object, computed by dividing the mass by the volume of the object. Units are kilograms per cubic meter (kg/m3), or grams per cubic centimeter (g/cm3). fusion Mechanism of energy generation in the core of the Sun, in which light nuclei are combined, or fused, into heavier ones, releasing energy in the process. Fusion might not take place if altered. 6. What is antimatter? What would be the result if anti- matter and matter came into contact with one another? In the first few seconds the universe is a holocaust of relativistic particles, both matter and antimatter coexisting in an inferno of gamma rays. At t = 100 seconds and a temperature of 10 9 K, the density has dropped to 10 4 grams/ cm 3 nearly 1000 times as dense as lead. The gamma rays have cooled and are now X-rays. Of the initial sea of elementary particles only nucleons protons and neutrons and electrons remain-the building blocks of atoms. 7. What do we mean by a neutrino? What is the impor- tance of the solar neutrino experiment for astronomy, and what are the current results? neutrino Virtually massless and chargeless particle that is one of the products of fusion reactions in the Sun. Neutrinos move at close to the speed of light, and interact with matter hardly at all. solar neutrino problem The discrepancy between the theoretically predicted numbers of neutrinos streaming from the Sun as a result of fusion reactions in the core and the numbers actually observed. The observed number of neutrinos is only about half the predicted number. 8. What is equilibrium? What forces in a typical star maintain a state of equilibrium? What happens to a star if it deviates only slightly from equilibrium? The gravity-pressure balance that supports the sun is a fundamental part of stellar structure known as the law of hydrostatic equilibrium. It says that, in a stable star like the sun, the weight of the material press- ing downward on a layer must be balanced by the pressure of the gas in that layer. Hydro implies that we are discussing a fluid-the gases of the star. Static implies that the fluid is stable-neither expanding nor contracting. The law of hydrostatic equilibrium can prove to us that the interior of the sun must be very hot. Near the sun's surface, there is little weight pressing down on the gas, so the pressure must be low, implying a low temperature. As we go deeper into the sun, the weight becomes larger, so the pressure, and therefore the temperature, must also increase. 9. What is meant by a stellar model? How does the study of a stellar model allow astronomers to understand the interior structure of a star? Since our stellar models tell us that massive stars should evolve faster than low mass stars, we expect to see differences in the star clusters based on the mass of the stars. One clear indication that our models are at least on the right track is that we find no star clusters with O and B main sequence stars and many giants and supergiants. Observatins show us that when giants and supergiants are present in the clusters, there are few if any massive stars (O and B stars) on the main sequence. We can take models of many different masses of stars and determine what a cluster should look like after a given time. We can then compare the H-R diagram from our model with that of the observations of actual clusters to see how well they agree. For the most part, the agreement is quite good. 10. Why does the mass-luminosity relationship exist? What are its implications for the lifetime of a star? mass A measure of the total amount of matter contained within an object. mass-luminosity relation The dependence of the luminosity of a main-sequence star on its mass. The luminosity increases roughly as the mass raised to the third power. 11. What are the various layers of the Sun? What type of spectrum does each layer produce? Explain. corona The tenuous outer atmosphere of the Sun, which lies just above the chromosphere, and at great distances turns into the solar wind. coronal hole Vast regions of the Sun's atmosphere where the density of matter is about 10 times lower than average. The gas there streams freely into space at high speeds, escaping the Sun completely. convection zone Region of the Sun's interior, lying just below the surface, where the material of the Sun is in constant convective motion. This region extends into the solar interior to a depth of about 200,000 km. solar core The region at the center of the Sun, with a radius of nearly 200,000 km, where powerful nuclear reactions generate the Sun's energy output. 12. What is the meaning of the term convection? What direct evidence is there that convection occurs in the Sun? convection Churning motion resulting from the constant upwelling of warm fluid and the concurrent downward flow of cooler material to take its place. 13. How is it known that the solar corona is very hot? corona The tenuous outer atmosphere of the Sun, which lies just above the chromosphere, and at great distances turns into the solar wind. 14. What is the sunspot cycle? How are sunspots believed to arise? solar core The region at the center of the Sun, with a radius of nearly 200,000 km, where powerful nuclear reactions generate the Sun's energy output. APPLYING YOUR KNOWLEDGE 1. Hypothesis: The Sun's energy comes from a slow contraction and conversion of gravitational potential energy. Question: Present evidence for or against the hypothesis. Once the inner core begins to change to iron, our high-mass star is in trouble. Nuclear fusion involving iron does not produce energy, because iron nuclei are so compact that energy cannot be extracted by combining them into heavier elements. In effect, iron plays the role of a fire extinguisher, damping the inferno in the stellar core. With the appearance of substantial quantities of iron, the central fires cease for the last time, and the star’s internal support begins to dwindle. The star’s foundation is destroyed, and its equilibrium is gone forever. Even though the temperature in the iron core has reached several billion kelvins by this stage, the enormous inward gravitational pull of matter ensures catastrophe in the very near future. Gravity overwhelms the pressure of the hot gas, and the star implodes, falling in on itself. the neutrons in the shrinking core play a role similar in many ways to that of the electrons in a white dwarf. When far apart, they offer little resistance to compression, but when brought into contact, they produce enormous pressures that strongly oppose further contraction. The collapse finally begins to slow. By the time it is actually halted, however, the core has overshot its point of equilibrium and may reach a density as high as 1018 kg/m3 before beginning to re-expand. Like a fast-moving ball hitting a brick wall, the core becomes compressed, stops, then rebounds-with a vengeance! 2. Suppose the energy generated in the core of a star were to increase suddenly, and that a new state of equilibrium could not be attained rapidly. What would occur and why? The collapse finally begins to slow. By the time it is actually halted, however, the core has overshot its point of equilibrium and may reach a density as high as 1018 kg/m3 before beginning to re-expand. Like a fast-moving ball hitting a brick wall, the core becomes compressed, stops, then rebounds-with a vengeance! 3. What would happen if a balloon filled with air at room temperature 300 K were submerged in liquid nitrogen 78 K? Why? 4. Why is radiation pressure more important in hot stars than in cool stars? Recall that radiation pressure is the outward force due to a high density of photons traveling radially outward from the core of the Sun. (Technically they do not travel *exactly* radially outward because they suffer some scattering/absorption on their way out!) Hot stars will have more photons simply because the temperature is higher. Why? Because of the Stefan-Boltzmann Law! More radiation pressure is in hot stars and less radiation pressure is in cool stars. 5. Why is it not possible for you to compress an inflated balloon with your hands? Assume your hands are large enough to encompass the balloon. Explain the source of the forces involved. What is inside the balloon? A gas, mainly CO_2 if you blew it up using your lungs! So we have a gas of molecules. If you try to compress the gas, the temperature goes up because the density goes up (recall the IDEAL GAS LAW). The pressure must therefore go up, acting in such a way to work against the inward force by your hands. Recall that pressure is defined as a force per unit area. 6. Why is blueshifted granulation brighter than the surrounding darker regions that are redshifted? Recall that the first observations of a granulated solar surface provided strong evidence for our solar model that predicts a convective layer in the solar interior, just below the "surface." Because it is convective, we expect the dark regions to be a lower temperature, and therefore sinking, while the bright spots are the rising parcels of gas whose temperatures are higher. This is observed by noting the redshifts and blueshifts in their spectra! Since the dark regions (redshifted) are lower temperatures (because they are the parcels that are sinking), then according to the Stefan-Boltzmann Law they must be less bright than the rising hot parcels of gas. granulation Mottled appearance of the solar surface, caused by rising (hot) and falling (cool) material in convective cells just below the photosphere. 7. Present at least two arguments-one based on obser- vation and one based on theory-that the temperature of the Sun increases from the surface inward. Observations of absorption lines in the spectrum indicate the temperature must be higher in the solar interior. Observations of limb darkening (the Sun is fainter near the "edges") also indicate a cooler, more tenuous layer of gas in the outer layers of the Sun. From a theory viewpoint, if the Sun were not increasing in temperature inward then it could not preserve hydrostatic equilibrium the force of gravity at different radii within the Sun is different. 8. Suppose a rotating star had a large starspot on one side. How might the presence of the spot be detected by an observer on Earth? >9. Verify that charge and atomic mass number are both conserved in each of the reactions in the CNO cycle. >10. How large is the largest sunspot visible in Figure 16- 16? How large is the smallest? Express your answers in kilometers, and compare your answers with the diameter of the Earth. >11. Use Figure 16-21 to determine the percentage variation of sunspot number from cycle to cycle. >12. Determine the height above the photosphere of the prominence shown in Figure 16-31a in both kilometers and Earth diameters. Similarly, estimate the apparent length of the prominence. >13. Use Figure 16-21 to predict when the next sunspot maximum will occur. Use the figure to predict the part of the cycle the Sun is currently in. >14. Although a photon is a massless particle, it behaves as though it has a mass. Use Einstein's equation to find the apparent mass of a photon whose wavelength is 5000 A. Hint: How is wavelength related to a photon's energy? >15. If the typical human eye is able to resolve one minute of arc, how large would a sunspot have to be for it to be seen with the naked eye? Express your answer both in kilometers and in Earth diameters. Chapter 17 Page 387 SUMMARY QUESTIONS 1. What is the picture that astronomers have of the formation of stars? Include in your answer a descrip- tion of the path that a protostar takes to the main se- quence, the conditions under which stars are believed to form, and the significance of the fact that O and B stars are often found associated with gas and dust. The evidence for star formation in the Orion nebula includes the existence of hot, young short-lived main sequence stars, T Tauri stars, evidence of bipolar flows, emission nebulae, and a dark molecular cloud setting immediately behind the nebula. Hot, young main sequence stars have very short lives which implies that the stars must have formed recently, within the last few million years. We believe that stars form out of dark molecular clouds, so recent star formation should be found near such clouds. Observatins show us that when giants and supergiants are present in the clusters, there are few if any massive stars (O and B stars) on the main sequence. Star formation, so that bright and short-lived O & B stars are found there. The greatest concentrations of stars are found in the nuclear bulge. protostar Stage in star formation when the interior of a collapsing fragment of gas is sufficiently hot and dense that it becomes opaque to its own radiation. The protostar is the dense region at the center of the fragment. 2. What is the significance of the main sequence in terms of the results of stellar model calculations? Since our stellar models tell us that massive stars should evolve faster than low mass stars, we expect to see differences in the star clusters based on the mass of the stars. One clear indication that our models are at least on the right track is that we find no star clusters with O and B main sequence stars and many giants and supergiants. Observatins show us that when giants and supergiants are present in the clusters, there are few if any massive stars (O and B stars) on the main sequence. We can take models of many different masses of stars and determine what a cluster should look like after a given time. We can then compare the H-R diagram from our model with that of the observations of actual clusters to see how well they agree. For the most part, the agreement is quite good. 3. Why are the interiors of dust clouds favorable for the formation and continued existence of interstellar molecules? Dust Grain a small pin-point sized piece of carbon-rich material found in the ISM. 4. What are the physical conditions that exist in giant molecular clouds? Include density, temperature, and masses. Why are these conditions favorable for star formation? molecular cloud A cold, dense interstellar cloud which contains a high fraction of molecules. It is widely believed that the relatively high density of dust particles in these clouds plays an important role in the formation and protection of the molecules. molecular cloud complex Collection of molecular clouds that spans as much as 50 parsecs and may contain enough material to make millions of Sun-sized stars. molecule A tightly bound collection of atoms held together by the electromagnetic fields of the atoms. Molecules, like atoms, emit and absorb photons at specific wavelengths. 5. What is the observational evidence that the variety of objects discussed in the chapter are indeed the precursors to stars? helium and hydrogen gas and dust molecular cloud complex Collection of molecular clouds that spans as much as 50 parsecs and may contain enough material to make millions of Sun-sized stars. 6. How do observations of one young star cluster differ from observations of a somewhat older cluster? Explain your reasoning. star cluster A grouping of anywhere from a dozen to a million stars which formed at the same time from the same cloud of interstellar gas. Stars in clusters are useful to aid our understanding of stellar evolution because they are all roughly the same age and chemical composition, and lie at roughly the same distance from Earth. APPLYING YOUR KNOWLEDGE 1. How would the spectrum of a protostar having both substantial mass loss from a strong wind and substan- tial accretion from surrounding material differ from that of a star having neither of these traits? 2. What characteristic of the objects shown in Figure 17- 16 causes the spectrum in the infrared to deviate from that of a blackbody? The spectrum is not the pure shape of the Plank curve because of the presence of dust and the eventual production of a disk of material containing a large dust content. Remember that the dust radiates strongly in the infrared (IR), so there is an additional hump in the spectrum in the IR, as seen in Figure 17-16. 3. Given that a high-mass star has more hydrogen than a low-mass star, why does a high-mass star remain on the main sequence for a shorter time? A high mass star will provide stronger gravity and therefore can compress the gas in the star at a much higher rate. This increases the rate of nuclear burning (H to He) in the core of the star. The high mass stars will have a shorter lifetime. 4. Why might it be possible to simply look at Figure 17-19 and deduce that the bright stars in it are young? There are a few singposts that these might be young stars: the blue reflection nebula indicates the presence of dust, the stars are bright and blue, an indication that they are hot and likely newly formed massive stars that the massive stars are formed first!. I had seen about 12 very bright stars among the fainter stars. The Plelades star cluster. 5. In what ways do observations of molecular clouds, bipolar flows, OB associations, Bok globules, T Tauri stars, FU Orionis stars, and Herbig-Haro objects discussed above all provide data relating to star formation? All of these objects are related to one another, but arise from their own mechanism (in ohter words, if you see one, then you might expect to observe the other). In addition, they are predicted from our theory of star-formation. >6. Consider an object similar to that shown in Figure 17- 18 in which two Herbig-Haro objects are ejected from a central object. Suppose the central source has a spec- tral line at 6000 A. Suppose further that one component has the same spectral line at 6002 A, while the other component has the same line at 5997 A. How fast is each component moving with respect to the source, and with respect to each other? What implicit assump- tion about the motion are you making? >7. Figure 17-3 is an infrared contour map of the central region of our galaxy. If the distance from the Sun to the center of our galaxy is 8,500 parsecs, what is the size in kilometers of the infrared region shown? Hint: Think about the angular size formula. >8. Compute what temperature the protosun had when its luminosity and radius were each 1000 times the present values? Hint: In Chapter 15 we saw a relationship between the luminosity, temperature, and radius. All we need to do is apply the Luminosity/Temperature/Radius relation and take a ratio. Here is what we know: L = 1000 solar luminosities, and R = 1000 solar radii. We know that L/R^2 is proportional to T^4 L/R^2 = 1000/(1000^2) = 10^(-3) Now, to get T(protosun), we need to raise that to the 1/4 power. T(protosun) = 10^(-3/4) = 0.1778 T(sun) Since we know the surface temperature of the Sun is 5800K, then the temperature of the protosun was about: T(protosun) = 0.1778 x 5800K = 1028K Chapter 18 Page 409 SUMMARY QUESTIONS 1. Why must a star inevitably leave the main sequence? How is the length of time a star spends on the main sequence affected by such things as the star's mass and luminosity? Stellar Masses More than any other stellar property, mass determines a star's position on the main sequence. Low-mass stars are cool and faint, they lie at the bottom of the main sequence. Very massive stars are hot and bright; they lie at the top of the main sequence. Newborn Star on the H-R Diagram The changes in a protostar’s observed properties are shown by the path of decreasing luminosity, from stage 4 to stage 6. At stage 7, the newborn star has arrived on the main sequence. A star like the Sun, for example, after spending a few tens of millions of years in formation (stages 1-6 in Chapter 11), will reside on or near the main sequence (stage 7) for roughly 10 billion years before evolving into something else. core hydrogen burning The energy burning stage for main sequence stars, in which the helium is produced by hydrogen fusion in the central region of the star. A typical star spends up to 90% of its lifetime in hydrostatic equilibrium brought about by the balance between gravity and the energy generated by core hydrogen burning. 2. What are the internal and visible changes that take place in a star after its main-sequence evolution? Answer in terms of the physical processes that are taking place. Why does the internal temperature of a star rise when its core nuclear fuel is exhausted? As soon as hydrogen becomes substantially depleted, about 10 billion years after the star arrived on the main sequence, the helium core begins to contract. The shrinkage of the helium core releases gravitational energy, driving up the central temperature and heating the overlying layers, causing the hydrogen there to fuse even more rapidly than before. Figure 12.3 depicts this hydrogen-shell-burning stage, in which hydrogen is burning at a furious rate in a relatively thin layer surrounding the nonburning inner core of helium "ash." The hydrogen shell generates energy faster than did the original main-sequence star’s hydrogen-burning core, and the shell’s energy production continues to increase as the helium core contracts. Strange as it may seem, the star’s response to the disappearance of the nuclear fire at its center is to get brighter! 3. What does the evolutionary track of a 1-solar-mass star on the Hertzsprung-Russell diagram look like? Relate the luminosity, surface temperature, radius of the star, internal structure, and physical processes taking place in the star to its position along the evolutionary track. Do the same for a 10-solar-mass star. Algol is a binary system of a five-solar-mass main-sequence star and a one-solar-mass giant. This presents a paradox because high-mass stars evolve faster than low-mass stars, so the five-solar-mass star should leave the main sequence stage before the one-solar-mass star. The resolution of this paradox lies in mass transfer. Suppose that the system is originally composed of a 5-solar-mass star and a one-solar-mass star. After about 200 million years the five-solar-mass star will run out of hydrogen in the core and will expand to become a red giant. If, as it expands, the star fills its Roche lobe, material will be drawn off of the five-solar-mass star and deposited onto the one-solar-mass star still on the main sequence. This can continue until four solar masses of material is transferred from the giant to the main-sequence star, resulting in a five-solar-mass main sequence star and a one-solar-mass giant. 4. What unusual properties distinguish a degenerate gas from a normal gas? How are these properties responsible for the helium flash? How are they important for the structure of white dwarf stars? helium flash An explosive event in the post-main-sequence evolution of a low-mass star. When helium fusion begins in a dense stellar core, the burning is explosive in nature. It continues until the energy released is enough to expand the core, at which point the star achieves stable equilibrium again 5. What are the nuclear reactions in the triple-alpha reaction? What are the physical conditions under which the reaction takes place? When in the life- time of a star is the triple-alpha reaction important? 6. Where is the Cepheid instability strip in the Hertzsprung-Russell diagram? What is its significance? High-mass Cepheids have greater luminosities and radii than low-mass Cepheids. Because high-mass stars are both greater in mass and radius, they will pulsate more slowly than the lower-mass Cepheids. Therefore, high-luminosity Cepheids pulsate more slowly and have longer periods than the lower-luminosity Cepheids. A period-luminosity relation exists for the Cepheid and RR Lyra variable stars. This relationship between a star's luminosity and its pulsation period allows astronomers to determine the luminosity (absolute magnitude) of the star by simply measuring the pulsation period of the star. The apparent magnitude of the star can be determined by simply measuring the brightness of the star. 7. What characteristics might a dying star be expected to exhibit? How do these compare with the known properties of white dwarfs? What is the role of the Chandrasekhar mass limit in the theory of white dwarfs? white dwarf A dwarf star with a surface temperature that is hot, so that the object glows white. white dwarf A dwarf star with a surface temperature that is hot, so that the object glows white. The white dwarf continues to cool and dim with time, following the white-yellow-red line, eventually becoming a black dwarf-a cold, dense, burned-out ember in space. This is stage 14, the graveyard of stars. The cooling dwarf does not shrink much as it fades away, however. Even though its heat is leaking away into space, gravity does not compress it further. Its tightly packed electrons will support the star even as its temperature drops (after trillions of years) almost to absolute zero. As the dwarf cools, it remains about the size of Earth. 8. What evidence is there that planetary nebulae are an intermediate stage between red giants and white dwarfs? How does mass loss affect the possibility that a given star may become a white dwarf? What is the approximate maximum initial mass of stars that eventually become white dwarfs? A planetary nebulae is an object with a small, dense core (central blue-white star) surrounded by an extended shell (or shells) of glowing matter. (a) The Helix Nebula appears to the eye as a small star with a halo around it. About 140 pc from Earth and 0.6 pc across, its apparent size in the sky is roughly half that of the full Moon. (b) The appearance of a planetary nebula can be explained once we realize that the shell of glowing gas around the central core is quite thin. There is very little gas along the line of sight between the observer and the central star (path A), so that part of the shell is invisible. Near the edge of the shell, however, there is more gas along the line of sight (paths B and C), so the observer sees a glowing ring. (c) The Cat’s Eye Nebula is an example of a much more complex planetary nebula. It lies about 1000 pc away. It may have been produced by a pair of binary stars (unresolved at the center) that have both shed planetary nebulae. As the dwarf cools, it remains about the size of Earth. 9. What observational evidence is there for stellar evo- lution? How would the Hertzsprung-Russell diagram of a star cluster be expected to evolve over time? As the core shrinks, the gravitational pull in its vicinity eventually becomes so great that nothing-not even light-can escape. The resultant object therefore emits no light, no other form of radiation, no information whatsoever. Astronomers call this bizarre endpoint of stellar evolution, in which the core of a very-high-mass star collapses in on itself and vanishes forever, a black hole. Star clusters provide excellent test sites for the theory of stellar evolution. Every star in a given cluster formed at the same time, from the same interstellar cloud, with virtually the same composition. 10. What observations of stellar chemical compositions have a bearing on studies of stellar evolution? helium and hydrogen. Dust: Tiny grains of stuff, e.g., carbon grains (soot) and silicate grains (sand) that are about 0.1-1.0 micron in size. Dust grains are a major component of the interstellar medium. Dust blocks visible light causing interstellar extinction. Dust scatters incident starlight, particularly the blue wavelengths of light blue light has a wavelength comparable to the dust grain's size causing interstellar reddening. The dust itself is cold, and cools even further by giving off infrared emission. APPLYING YOUR KNOWLEDGE 1. Hypothesis: The Sun is hollow. Use all your astronomi- cal knowledge to argue against this hypothesis. The Sun is not hollow since it is burning helium gas, and hydrogen gas. Alot of gas appears to come from the inside of the sun. 2. How do observations of the presence of certain elements in a star's atmosphere provide information about stellar evolution? From Chapter 17, observations of Lithium generally indicate youngs stars. The radioactive element technetium is present in some stars. With a relatively short half-life, it can be present only if star-formation was recent. Finally, the presence of barium in certain stars provides information on convection and the transfer of mass between stars in a binary system. 3. Why is the observed main sequence not an infinitely thin line on the H-R diagram? Two main reasons are sought: one observational and one theoretical. 4. Stars do not evole up or down the main sequence. From what you know of the properties of stars on the main sequence what would have to happen to a star to make it evolve up the main sequence? the main-sequence is a group of stars burning H to He in their cores having a range of masses that increases from the bottom right to high at the top left. The only way for a star to "move" along the main-sequence would be for it to continuously gain substantial amounts of mass. The star becomes cold, and cool as the star runs out of the helium gas, and and hydrogen gas. 5. Summarize the events occurring at each point in Figure 18-3. >6. What percentage of its mass would a 10-solar-mass star lose in 10 5 years if it were losing mass at a rate of 10 -5 solar mass per year? >7. Use the formula for the main-sequence lifetime, along with the mass-luminosity relation, to compare the lifetimes of stars of 0, 1, 1, 10, and 20 solar masses. Chapter 19 Page 435 SUMMARY QUESTIONS 1. What do we mean by the term nova? What are two pieces of evidence that novae eject mass? A nova occurs when hydrogen fuses on the surface of a white dwarf. This generally happens as mass is transferred from a giant to a white dwarf in a binary system; neither star is greatly affected by this process. A supernovae can occur if the mass transfer causes the white dwarf to exceed the Chandrasekhar limit resulting in a sudden collapse of the entire star. A supernova can also occur when the iron core of a massive star rapidly collapses. In both types of supernova shock waves rip apart and drastically alter the stars, in a nova no collapse occurs, just the fusion of hydrogen on the surface of the white dwarf. 2. Why do astronomers conclude that the size of an object is about equal to the light-travel time across it? 3. What model for novae phenomena best allows astronomers to understand them? Standard Candle: Any astronomical object of known luminosity that can be used to obtain a distance. Cepheid variables, Main sequence stars, and type I supernovae have all be used as standard candles. Supernovae come in two types: Type I is caused by sudden nuclear burning in a white dwarf star. Type II is caused by the collapse of the core of a supermassive star at the end of its nuclear-burning life. In either case, the star is destroyed and the light given off in its explosion briefly rivals the total light given off by a whole galaxy. 4. What are the observed features of the Crab Nebula? What evidence exists that it is indeed the object observed abot 1000 years ago by Chinese astronomers? supernova remnant The scattered glowing remains from a supernova that occurred in the past. The Crab Nebula is one of the best-studied supernova remnants. One of the best-studied supernova remnants is the Crab Nebula. Its brightness has greatly dimmed now, the original explosion in the year A.D. 1054 was so brilliant that it is prominently recorded in the manuscripts of Chinese and Middle Eastern astronomers. For nearly a month, this exploded star reportedly could be seen in broad daylight. Even today, the knots and filaments give a strong indication of past violence. The nebula-the envelope of the high-mass star that exploded to create this Type II supernova-is still expanding into space at several thousand kilometers per second. 5. What are the observed differences between ordinary novae and supernovae? Explain them in terms of the violence of the explosion, the increase in bright- ness of the object, and the amount of mass expelled. One such global method is based on observations of Type I (carbon detonation) supernovae. (Sec. 12.5) Recall that these objects are both very bright and have a remarkably narrow spread in luminosities, making them particularly useful as standard candles. (Sec. 15.2) They can be used as probes of the universe because, by measuring their distances (without using Hubble’s law) and their redshifts, we can determine the rate of cosmic expansion in the distant past What of Type I supernovae? Is there more than one way for a supernova explosion to occur? The answer is yes. To understand the alternative supernova mechanism, we must reconsider the long-term consequences of the accretion-explosion cycle that causes a nova. A nova explosion ejects matter from a white dwarf’s surface, it does not necessarily expel or burn all the material that has accumulated since the last outburst. In other words, there is a tendency for the dwarf’s mass to increase slowly with each new nova cycle. As its mass grows and the internal pressure required to support its weight rises, the white dwarf can enter into a new period of instability-with disastrous consequences. the characteristics of Type II supernovae are exactly consistent with the core collapse supernovae discussed in the previous section. The Type II light curve is in good agreement with computer simulations of a stellar envelope expanding and cooling as it is blown into space by a shock wave sweeping up from below. In addition, since the expanding material consists mainly of unburned hydrogen and helium, it is not surprising that those elements are strongly represented in the supernova’s spectrum. 14. What evidence do we have that many supernovae have occurred in our Galaxy? We have plenty of evidence that supernovae have occurred in our Galaxy. Occasionally, the supernova explosions are visible from Earth. In other cases, we can detect their glowing remains, or supernova remnants. 6. In what ways do Type I and Type II supernovae differ? Your answer should be based on their observed properties and the models we have to explain them. Type I supernovae are more luminous than Type II supernovae and decline in brightness in a more regular manner. The Type I supernovae also show almost no hydrogen lines in their spectra, while Type II supernovae show very strong hydrogen lines in their spectra. Type II supernovae are believed to be produced when the iron core of a massive star collapses. Type I supernovae, on the other hand, are believed to be produced when mass from a binary companion accumulates on a white dwarf and pushes it over the Chandrasekhar limit. The white dwarf collapses and produces a supernova, incinerating the whole star. 7. How do supernovae provide us with direct evidence for the synthesis of heavy elements within stars? Name and describe three basic processes by which heavy elements are synthesized. 8. Describe the interior structure of a neutron star. Neutron stars and white dwarfs are similar in that both are at the end points of stellar evolution, have high surface temperatures, no longer produce energy via thermonuclear fusion, are composed of degenerate matter, have very small radii and are very dense. Neutron stars and white dwarfs are different in that neutron stars are the cores of massive stars that went through a supernova, while white dwarfs are the cores of intermediate- mass stars that produced planetary nebulae. (White dwarfs can also be formed by low mass stars whose outer layers sort of evaporate, but the universe isn't old enough for any of this to have formed in this way.). Additionally, neutron stars are hotter and more compact than white dwarfs. Consequently they have stronger magnetic fields, rotate faster, and radiate larger amounts of short wavelength energy (e.g. x-rays) and can produce synchrotron radiation. The upper limit on the mass of a neutron star is set by the maximum pressure that a degenerate neutron gas can provide. At extremely high pressure the neutrons will become degenerate and the pressure that supports the weight of the star comes from the degenerate neutrons. If the mass is greater than 2 or 3 solar masses, then the degenerate pressure of the neutrons is not sufficient to support the outer layers and the neutrons will be driven into each other. There is no known method to keep the material from collapsing to a point when this occurs. The only option that could produces the pulses observed and not destroy the star was a rotating neutron star. 9. What evidence is there that pulsars are actually rotating neutron stars? What observational evidence is there for the existence of pulsars? Conservation of angular momentum tells us that as rotating objects are drawn closer to the rotation axis, the object will spin faster. In producing a neutron star, the core of a star is spinning and begins to collapse. The collapsing core must conserve angular momentum, and since it will decrease its radius by a large amount, it will spin much faster than a normal star. Neutron stars are very hot but not very luminous because they have very small surface areas. Recall that the luminosity of an object depends on both its temperature and its size. The radius of a neutron star is typically 100,000 times smaller than that of a main sequence star. If a neutron star were 10 times hotter than a main sequence star (e.g. 100,000 K) and 100,000 times smaller, then the luminosity of the neutron star would be 1 million times less than that of a main sequence star. Theory predicts that the magnetic field of the star will be frozen into the star so that as it collapses it becomes much stronger because it is packed into a smaller and smaller region. Astronomers were able to show that pulsars could not be pulsating normal stars because the duration of the pulse (that is, the period of pulsation) was so short that the stars had to be smaller than 300 km in diameter. Not even white dwarfs are this tiny. Additionally, normal stars, including white dwarfs, do not posses a gravitational field that is strong enough to hold them together under the violent (rapid) pulsations that would be required to produce the observed pulses. Normal stars could also not rotate fast enough and remain intact to produce the observed pulses. Finally, neutron stars would vibrate much too fast and with too small an amplitude to produce the observed pulses. 10. How do light and matter behave near a blach hole? Why can nothing escape from a black hole? black hole A region of space where the pull of gravity is so great that nothing-not even light-can escape. A possible outcome of the evolution of a very massive star. event horizon Imaginary spherical surface surrounding a collapsing star, with radius equal to the Schwarzschild radius, within which no event can be seen, heard, or known about by an outside observer. 11. How might astronomers detect a black hole? What evidence is there tha the Cygnus X-1 system actually consists of a giant star and a black hole, rather than some other collapsed object such as a white dwarf or a neutron star? A few close binary systems, however, have peculiarities suggesting that one of their members may be a black hole. Figure 13.14(a) shows the area of the sky in the constellation Cygnus, where the evidence is particularly strong. The rectangle outlines the celestial system of interest, some 2000 pc from Earth. The black-hole candidate is an X-ray source called Cygnus X-1, discovered by the Uhuru satellite in the early 1970s. Its visible companion is a blue B-type supergiant. Assuming that it lies on the main sequence, its mass must be around 25 times the mass of the Sun. Spectroscopic observations indicate that the binary system has an orbital period of 5.6 days. Combining this information with spectroscopic measurements of the visible component’s orbital speed, astronomers estimate the total mass of the binary system to be around 35 solar masses, implying that Cygnus X-1 has a mass of about 10 times that of the Sun. X-ray radiation emitted from the immediate neighborhood of Cygnus X-1 indicates the presence of high-temperature gas, perhaps as hot as several million kelvins. Scientists infer that the energy-emitting region in Cygnus X-1 must be very small because of the rapid variability of the radiation received. 12. What is the basic model that explains most of the objects in the astronomical zoo? APPLYING YOUR KNOWLEDGE 1. Outline the steps leading to the inference that Cygnus X-1 and V404 Cyg might or might not be black holes. Look for regions in space that are emitting gamma rays and x-rays. There is a problem, however, because other objects such as neutron stars also emit x-rays. In order to distinguish between them, we need to look at mass-->black holes will have a higher mass than neutron stars. If the mass is less than 2 1/2 solar masses, it is a neutron star. If it is greater than 2.5-3 solar masses, then it is a black hole. The object Cygnus X-1 has been observed in x-rays to have a period of 5.6 days. It is a binary star, which explains that its brightness changes regularly every 5.6 days, since the star is being eclipsed regularly by the other object in the binary system. Not only is this a binary system, but it also emits x-rays and radio waves. Since it is a binary star, we can determine the mass of the thing we can see and the thing we can't see. The mass of the unseen object has been determined to be around 8 solar masses. It has been concluded that one of the objects in the binary system is a black hole. 2. What evidence might Tycho Brahe have used when he said that the supernova of 1572 was farther away than the Moon? Remember, this was prior to the telescope! He was unable to observe parallax, showing that the object was well beyond the Moon for which parallax was observed. If a galaxy contains a supernova that at its brightest has an apparent magnitude of 17, how far away is the gal- axy? Assume that the absolute magnitude of the supernova is -19. Proper motion also provides more evidence that Sgr A* is a black hole. Most people believe that Sgr A* is a supermassive black hole. With a radius of about 0.01 pc2 and an estimated mass of 2.6 million times the mass of the Sun, a supermassive black hole seems a probable explanation. Mass estimates are found using the proper motion of Sgr A* and stars in its vicinity2. 3. Your body consists of numerous chemical elements, including carbon, oxygen, and iron. Discuss the origin of these elements in terms of their formation in stars. Carbon and oxygen are formed as a result of He burning and subsequent nuclear reactions involving alpha particles (He nucleus). Iron (Fe) only forms in the most massive stars at the end of a long set of reactions involving numerous nuclei. These reactions only occur in the cores of massive stars where the temperatures are extremely high. Note that for each successive nuclear reaction involving a heavier element the reaction rates increase and it takes a shorter amount of time. >4. Supose the spectrum of a nova contains the HB spectral line observed at a wavelength of 4856 A. Remembering that HB is normally at a wavelength of 4861 A, calculate how rapidly the gaseous envelope expands. 4861 - 4856 =0005 >5. Novae usually show broad emission lines caused by the expanding gas. Suppose such a spectral line is observed to be 10 A wide. Using the observed width of the emission line, determine the speed of expansion of the gaseous envelope relative to the star itself. >6. What would be the size of a pulsar whose brightness changes substantially in 0.00007 seconds? >7. What would be the mass of a black hole whose binary companion is a 20-solar-mass star separated by 0.175 AU and whose period is 5 days? 0.175 x 5 = 0.875 Chapter 20 Page 466 SUMMARY QUESTIONS 1. Why did early star counts lead to an erroneous picture of the size of the Galaxy and the location of the Sun within it? How was Harlow Shapley able to improve this picture? Early in the twentieth century, the American astronomer Harlow Shapley used observations of RR Lyrae stars to make two very important discoveries about the Galactic globular cluster system. First, he showed that most globular clusters reside at great distances-many thousands of parsecs-from the Sun. Second, by measuring the direction and distance of each cluster, he was able to determine their three-dimensional distribution in space. In this way, Shapley demonstrated that the globular clusters map out a truly gigantic, and roughly spherical, volume of space, about 30 kpc across. Harlow Shapley used observations of RR Lyrae stars to determine distances to the globular clusters. 2. What is the modern picture of our galaxy? Include the Galaxy's dimensions and the location of the Sun, halo, disk, and nucleus. galactic halo Region of a galaxy extending far above and below the galactic disk, where globular clusters and other old stars reside. galactic disk Flattened region of gas and dust that bisects the galactic halo in a spiral galaxy. This is the region of active star formation. galactic nucleus Small central high-density region of a galaxy. Nearly all of the radiation from an active galaxy is emitted from the nucleus. 3. What are several kinds of evidence for the existence of interstellar dust? How can the size of individual interstellar dust grains be estimated? What are the various lines of evidence that tell us about the composition of interstellar dust grains? interstellar dust Microscopic dust grains that populate the space between stars, having their origins in the ejected matter of long-dead stars. 4. How do interstellar absorption lines give us informa- tion about the interstellar medium? What conditions (temperature, mass, density, diameter) are present in interstellar clouds? Why are interstellar absorption lines generally difficult to observe from the ground? interstellar medium The matter between stars, composed of two components, gas and dust, intermixed throughout all of space. 5. What is the observational evidence for a multicompo- nent interstellar medium? gas and dust. 6. What is the process by which neutral atomic hydro- gen produces 21-cm emission? Why is 21-cm emission so important in astronomy? Because long-wavelength radio waves are largely unaffected by interstellar dust, and hydrogen is by far the most abundant element in interstellar space, the 21-cm signals are strong enough that virtually the entire disk can be observed in this way. The 18- to 21-cm range lies within the quietest part of the spectrum, where the Galactic "static" from stars and interstellar clouds happens to be minimized. Furthermore, the atmospheres of typical planets are also expected to interfere least at these wavelengths. The water hole seems like a good choice for the frequency of an interstellar beacon, although we cannot be sure of this reasoning until contact is actually achieved. 7. What evidence is there for the existence of spiral structure in the Galaxy? Why do astronomers believe star formation is taking place in the spiral arms? A proposed explanation for the existence of galactic spiral arms, in which coiled waves of gas compression move through the galactic disk, triggering star formation. spiral arm Distribution of material in a galaxy in a pinwheel-shaped design apparently emanating from near the galactic center. spiral galaxy Galaxy composed of a flattened, star-forming disk component which may have spiral arms and a large central galactic bulge. 8. How can study of the motions of stars using the Doppler effect be used to study the structure of the Milky Way? The Doppler effect is produced because the relative motion of the source and observer affects the time of arrival between the crests of adjacent waves in any wave phenomenon. If the observer is moving away from the source, the time between the arrival of one crest and the arrival of the next crest of the wave will be lengthened. 9. How are observations of neutral hydrogen HI used to study the rotation of the Galaxy and the distribution of gas within it? What are the main results of these observations, and what are the difficulties in interpret- ing them? 10. What evidence do astronomers have that unusual events occur near the galactic center? Although they do orbit the Galactic center, they move in all directions, their paths filling an entire three-dimensional volume rather than a nearly two-dimensional disk. At any given distance from the Galactic center, bulge or halo stars move at speeds comparable to the disk’s rotation speed at that radius but in all directions, not just one. Their orbits carry these stars repeatedly through the disk plane and out the other side. 8. Explain why galactic spiral arms are believed to be regions of recent and ongoing star formation. The spiral arms in our Galaxy are made up of much more than just interstellar gas and dust. radio observations of Galactic gas. The densities of both stars and gas in the disk decline quite rapidly beyond about 15 kpc from the Galactic center (although some radio-emitting gas has been observed out to at least 50 kpc). galactic center The center of the Milky Way, or any other, galaxy. The point about which the disk of a spiral galaxy rotates. 11. What are the old (incorrect) ideas about spiral structure and why don't they work? Describe the density-wave theory of spiral structure. The primary observational evidence against the spiral density wave theory is the existence of spurs and branches and the existence of multi-armed spiral galaxies. Computer simulations reveal that spiral density waves lead to two well defined spiral arms that radiate outward smoothly from the nuclear bulge. The Milky Way and many other spiral galaxies have spurs and branches sticking off of the spirals. Additionally, many of the spirals contain more than two well-defined arms. Therefore, though the overall idea of the density wave theory may be on the right track, it is clear that the theory is incomplete until it can explain these features. 12. What are three kinds of evidence for the existence of an overall galactic magnetic field? magnetic field Field which accompanies any changing electric field, and governs the influence of magnetized objects on one another. 13. What is the significance of cosmic rays? Where are they thought to form? high-energy particles called cosmic rays. A similar method is also useful for meteorites the exposed surface is constantly being hit by high-energy particles called cosmic rays these are strong enough to break a nucleus of a heavy element into a few smaller nuclei (ligher elements). 14. What is the difference between Populatin I and Population II objects? You should distinguish them on the basis of age, chemical composition, association with gas and dust, location within the Galaxy, motions, and orbital characteristics. How did these two popu- lations come to be, and how are the characteristics of each related to the origin and evolution of our galaxy? Population I is a irregular galaxy and a spiral galaxy. No for elliptical. Population II is a no for irregular, is a yes for spiral, and yes for elliptical. APPLYING YOUR KNOWLEGE 1. The star in the center of a reflection nebula is gener- ally a B star, typically B3 or cooler in spectral type. Why is it unlikely that a reflection nebula would be caused by a hotter star? 2. Show your understanding of how we analyze the spiral structure of the Milky Way by explaining Figures 20-19 and 20-20. I showed a similar diagram in lecture. The key in understanding these figures is to correctly apply the Doppler Effect. By noting the redshifts and blueshifts one can uncover the motions of the clouds in the disk. Remember that the strongest Doppler effect will be observed for movement along the observer's line of sight, while no Doppler effect will be observed for motion perpendicular to the observer's line of sight. Objects closer to the galactic center turn out to have somewhat faster orbital speeds. wavelength of line starts to rise up in a form of a u for B and down and up again higher wavelength for A. Intensity is going up Figure 20-19. a Plotting the location of hydrogen gas in the Galaxy from 21-cm observations. The gas in different parts of the Galaxy will have different Doppler shifts and different intensities, enabling positions within the Galaxy to be estimated. b The composite emission line detected by a radio telescope. FIGURE 20-20. Resolving ambiguities concerning the distribution of gas requires an assumption that the gas is distributed in a regular way in the Galaxy. a Plotting the location of hydrogen gas. b The compsite emission line. A or C (?) Goes up and down in a u shape and B. 3. Astronomers believe there are still undiscovered globular clusters within the Milky Way. Where might such clusters exist? Explain. Hint: Make a drawing of the Milky Way as seen edge-on, showing the Sun and the globular clusters. Recall that the galactic center serves as a HUGE source of extinction, such that we can not see the other side of the MW disk. It is possible that some globular clusters may reside there. 4. Explain how two stars can have identical spectra different colors. The intervening space between the observer and the star can cause the star's color to change. We called this interstellar reddening. The strength of the stellar lines in the spectrum however, will be unchanged. 5. Examine Figure 20-5. For which positions A, B, etc. will stars appear to move through the greatest angular distance relative to distant background stars during one year? The least angular distance? 6. Explain why the caption in Figure 20-15 says that the wings must come from hotter material than the core of the line. Energy > on left side of diagram Energy flows upward and downward in a u shape. 21- cm Wavelength> FIGURE 20-15 The narrow core of the lines comes from clouds of cold gas, but the broad "wings" must come from hotter material. 7. Explain how the methods used by Herschel and Kapteyn might be applied by a person lost in a forest to find the way out. What assumptions would the lost person be making? Assume the trees are uniformly distributed (isotropic). Then, count the trees in different directions. The direction toward which the tree count is largest would be toward the center; the direction toward which the count was least is the direction toward the edge. >8. What is the distance to a globular cluster inside of which an RR Lyrae star is observed that appears 3 X 10 -17 as bright as the Sun? Hint: You may want to refer to Section 15.6 as well as the H-R diagram for a globular cluster. >9. Using the distance of the Sun from the galactic center, and the speed with which it moves, what is the length of the galactic year? >10. Consider two stars having identical spectra different colors although they are at the same distance from Earth. Suppose the redder star appears two times fainter. How much farther away will the redder star appear to be? Explain why the redder one appears to be more distant. According to the inverse square law of light, the star must be 2^(1/2) times further away, or 1.41 times further away. >11. If a dust particle consists of gas atoms that stick together during collisions, and a typical atom is 1 to 2 A in diameter, what is the number of atoms in an average-sized dust grain? Make an order-of-magni- tude estimate, not a precise calculation. If a typical dust grain has a size of about 0.001 cm, which is 1000 Angstroms, the number of particles will be this number divided by the size per atom (1-2 Angstroms), giving a result of hundreds to thousands of atoms per dust particle. >12. Using the scale on Figure 20-27, determine the linear size of the smallest resolvable object in the galactic center region. Express your answer in light-years, astronomical units, and kilometers. Hint: Use the scale on the declination axis. Figure 20-27. radio image of the galactic center. -0.5 -75 pc -240 light-years. Sgr D IIII Sgr D SNR Sgr B2 Sgr B1 Arc Sgr A Snake SNR 359.1-00.5 Mouse SNR 359.0-00.9 above is on left side of galactic center below is on right side of galactic center SNR 0.9+0.1 New SNR 0.3-0.0 Threads New Features The Cane Background Galaxy Threads Sgr C Coherent Structure? Sgr E New Thread The Pelican Tornado SNR >13. If distances within the Milky Way were in error by a factor of two (i.e., if the Galaxy were actually twice as large as we thought), what would be the effect on the computed mass? Assume the observed periods of observed objects remain the same. >14. If a star at a distance of 15 light-years has a radial velocity of 150 km/sec, by what percentage does its distance from the Sun change in 100 years? Chapter 21 Page 498 SUMMARY QUESTIONS 1. How was the extragalactic nature of the galaxies discovered? Why were astronomers led astray by some observations? Observations made from the Hubble Space Telescope. Further support for the extragalactic nature of M31 came in 1925 when Hubble discovered variable stars in M31 that had similar properties to those detected earlier in the Large Magellanic Cloud. This provided a relative distance scale between the LMC and M31 and indicated that the M31 was located at a distance of 300 kpc. Hubble discovered Cepheid variables in most of the galaxies in the Local Group but, in this environment, redshift is not well-correlated with distance as the Local Group is loosely gravitationally bound. Observations of Local Group galaxies therefore would not reveal universal expansion. Hubble took spectra of fainter and smaller galaxies as well and noticed that their observed redshifts were considerably larger than anything in the Local Group. Hubble also noticed that galaxies which were faint and had small apparent angular sizes, tended to have larger redshifts than galaxies which appeared bigger and brighter. Lacking a suitable means for determining distances to these smaller and fainter galaxies, Hubble made some assumptions on the nature of these galaxies. By assuming that galaxies were either of constant brightness or constant physical diameter Hubble could deduce that the smaller and fainter galaxies with the higher redshifts were farther away than the brighter bigger galaxies with smaller redshifts. In this way, Hubble could make a plot of galaxy distance versus observed galaxy redshift. radio aources 2. What galaxy characteristics are used for their classification? Hubble's Categories Galaxy ID Numbers Defining Characteristics (describe the characteristics used by Hubble. elliptical irregular spiral Spirals are labeled as Sa, Sb, or Sc. All elliptical galaxies have n between 0 and 7. Irregular galaxies have no obvious spiral or elliptical structure. 3. What are the Population I and Population II character- istics of spiral, elliptical, and irregular galaxies? What is the role of star formation rate on the determination of galaxy type? Population I - young star, chemically like the Sun, their presence indicates that current star formation is going on. Population II - old stars dominate, metal deficient compositions, no new or significant star formation occurring . galaxies are very far away. 4. What is the chain of observations necessary to estimate the distances to galaxies, from the nearest to the farthest? What is the impact of different types of errors on the distance pyramid? OB stars - by looking at the brightest stars, you can sometimes get good distances, but these are only in certain types of galaxies and are often in regions of star formation that have quite a bit of dust. fuzzy spiral nebula (like Andromeda) were actually very distant, separate objects. if you can find a Cepheid in a galaxy, you can find the distance to that galaxy. And that is exactly what Hubble and Humason did. By using the Cepheid Period-Luminosity relation to determine the distance to the Andromeda Galaxy (one of our closer neighbors), he found that it was 900,000 light years away 5. What is the velocity-distance relation and how is it used to find distance? Velocity-Distance Relation among Extra-Galactic Nebulae. Figure 1: Radial velocities, corrected for solar motion, are plotted against distances estimated from involved stars and mean luminosities of nebulae in a cluster. The black discs and full line represent the solution for solar motion using the nebulae individually; the circles and broken line represent the solution combining the nebulae into groups; the cross represents the mean velocity corresponding to the mean distance of 22 nebulae whose distances could not be estimated individually. 6. What specific types of galaxies inhabit the Local Group? Local Group The small galaxy cluster that includes the Milky Way Galaxy. 7. What is the role of angular momentum in explaining differences among galaxy types? angular momentum problem The fact that the Sun, which contains nearly all of the mass of the solar system, accounts for just 0.3 percent of the total angular momentum of the solar system. This is an aspect of the solar system that any acceptable formation theory must address. 8. How do astronomers determine the fundamental properties of mass, size, and luminosity for galaxies and galaxy clusters? How do astronomers determine the fundamental properties of mass, size, and luminosity for galaxies Astronomers measure the temperature of stars by looking at their spectra and using Wien's Law. Stars range in temperature from a few thousand degrees Kelvin to over 25,000 K. (See the spectral classes.) Luminosity We measure the brightness of a lightbulb in watts (e.g. a 100-watt bulb, or a 300-watt halogen lightbulb) -- which measures how much energy is released per second. The Sun's luminosity is about 4×1026 watts. in an eclipsing binary the dimming of the pair of stars during eclipses can give information about the sizes of the stars. astronomers use orbital motion to measure mass. For example, you can use the orbits of Jupiter's moons to measure Jupiter's mass. For distant stars, astronomers can do the same calculation if there are two stars orbiting each other. (We need two stars because we cannot directly observe distance planets and moons.) Systems with two stars orbiting each other are called binary stars, and about half of all stars are in binary systems. Astronomers observe binaries to determine their orbital properties. the H-R diagram, which is a plot of stellar properties that shows that most of the different properties are closely related to each other. Distance I: Parallax Except for the Sun, all stars are very far away. Astronomers can measure the distance to some of the nearby stars using a technique of triangulation called parallax. As the Earth moves around the Sun, the position from which we view the stars changes. The observed position of a nearby star relative to background stars shifts slightly. If we can measure the shift, we can use geometry to compute the distance. (Diagrams and examples given in class.) Because distances were originally measured using parallax, astronomers usually quote astronomical distances in parsecs rather than light-years. A parsec is the distance at which the parallax angle is one arcsecond (parallax of one arcsecond -- get it?). One parsec equals about 3.26 light-years. 9. How do astronomers study the distribution of galaxies, galaxy clusters, and superclusters in space? What are some current results of such studies? Galaxy clusters are themselves clustered, forming titanic agglomerations of matter known as superclusters. When galaxies collide, the star formation rate often decreases or merge starburst galaxy Galaxy in which a violent event, such as near-collision, has caused a sudden, intense burst of star formation in the recent past. 10. What is the evidence that indicates the presence of nonluminous matter in galaxies and galaxy clusters? Virtually all galaxies seem to be immersed in vast clouds of nonluminous matter of unknown form called dark matter. The gravity of the dark matter affects the motions of the galaxies today, and it may even be responsible for the formation of the galaxies in the first place. Nonluminous matter (dust, etc.) creates bands or dark lanes that obscure starlight. nonluminous matter; exotic hypothetical particles. perhaps 90% of the mass in the universe is nonluminous. 11. What are the various ideas astronomers currently have concerning the formation of galaxies and galaxy clusters? In your discussion include the effects of density. galaxy cluster A collection of galaxies held together by their mutual gravitational attraction. density A measure of the compactness of the matter within an object, computed by dividing the mass by the volume of the object. Units are kilograms per cubic meter (kg/m3), or grams per cubic centimeter (g/cm3). 12. What effects might supernovae have had on the formation of spiral arms? supernova Explosive death of a star, caused by the sudden onset of nuclear burning (type I), or an enormously energetic shock wave (type II). One of the most energetic events of the universe, a supernova may temporarily outshine the rest of the galaxy in which it resides. supernova remnant The scattered glowing remains from a supernova that occurred in the past. The Crab Nebula is one of the best-studied supernova remnants. APPLYING YOUR KNOWLEDGE 1. If the Cepheid in the example in the text were actually a Type II Cepheid rather than the assumed Type I Cepheid, would its distance be larger or smaller than the originally computed distance? 2. Look at the image of M31 in Figure 1-15. What assumption might you make to allow you to determine the inclination of the galaxy to our line of sight? 3. Is it possible that the drawing of the Whirlpool galaxy in Figure 21-1a was completely accurate when the Third Earl of Rosse made it in the middle of the nineteenth century, and that the galaxy changed to the appearance shown in Figure 21-1b in the interven- ing 150 years? Present explicit arguments based on material discussed in this book. Figure 21-1a is a drawing of the nebula known as the Whirlpool, M51, made by the Earl of Rosse who ob- served the heavens with a giant 72-inch telescope. Figure 21-1b shows an image of the same object. The image shows much more detail than the drawing, and many of the details in the drawing are incorrect. 4. Classify everything you have in your own room into, at most, 10 categories. How might this classification scheme be useful to you? 5. Explain how our modern understanding of spectra allows us to say that there are fundamentally different classes of objects within the group of objects astrono- mers used to refer to as nebulae. 6. Explain the distance pyramid in your own words without a drawing. OB stars - by looking at the brightest stars, you can sometimes get good distances, but these are only in certain types of galaxies and are often in regions of star formation that have quite a bit of dust. fuzzy spiral nebula like Andromeda were actually very distant, separate objects. if you can find a Cepheid in a galaxy, you can find the distance to that galaxy. And that is exactly what Hubble and Humason did. To find out how faraway planets, and stars are, and the measurements give information as to how big in size the universe is. One way to measure the distance is Parallax measurements of the distances to the stars nearest Earth use as a baseline. The distances to the nearest stars can be measured using parallax Observation of the universe is seeing many galaxies, objects, planets, stars. 7. How do you implicitly use the idea of a standard candle to judge the distance to an oncoming car at night? Here, the basic assumption is that the intrinsic brightness (i.e. luminosity) of the headlight of every car is essentially the same. This is basically true. So, when the headlights are pointed directly into your eyes (i.e. along your line-of-sight), you don't pass if they are very bright. This is because you have some internal idea of how bright a headlamp really is! >8. Solve the example of the Cepheid distance given in the text assuming the star is a Type II Cepheid rather than the assumed Type I. By what percentage does the distance change? >9. Suppose the brightest blue star in a galaxy is 20 times brighter than the brightest Cepheid How much farther can astronomers see the blue star than a Cepheid? >10. What would be the angular size of a galaxy identical to the Milky Way if it were at a distance of 10 million light-years? If such a galaxy were observed to have an angular diameter 1/100 this size, what would its distance be? What assumptions did you make in finding this distance? >11. Look at the image of M31 in Figure 1-15. Compute the inclination of the galaxy to our line of sight. What assumption are you making in finding this angle? Note This problem requires basic knowledge of trigonometry. >12. If a supernova in a galaxy is observed to be 10 18 times fainter than the Sun, what is the galaxy's distance, assuming the supernova's luminosity is 10 9 times that of the Sun? >13. Suppose a galaxy is observed whose spectral lines of ionized calcium that normally would be at 3968 A are actually at 4268 A. What is the distance to this galaxy? What are you assuming in finding the distance? Chapter 22 Page 519 SUMMARY QUESTIONS 1. What are some of the principal types of radio galaxies? Why is it sometimes difficult to associate a radio galaxy with an optical counterpart? In a core-halo radio galaxy, most of the radio radiation is emitted from the small central region known as the galactic nucleus. The radio lobes of lobe radio galaxies are truly enormous. From end to end, an entire lobe radio galaxy typically is more than 10 times the size of the Milky Way Galaxy, comparable in size to the entire Local Group. Radio lobes are always found aligned with the center of the visible galaxy. radio galaxy Type of active galaxy that emits most of its energy in the form of long-wavelength radiation. Their optical spectra may show broad emission lines, indicating rapid internal motion within the energy-producing region. 2. What are the observations that distinguish Seyfert galaxies from other galaxies? A Seyfert galaxy looks like a normal spiral, but with a very bright galactic nucleus. The nucleus of a Seyfert is some 10,000 times brighter than the center of our Galaxy. In fact, the brightest Seyfert nuclei are 10 times more energetic than the entire Milky Way Galaxy. Seyfert galaxy Type of active galaxy whose emission comes from a very small region within the nucleus of an otherwise normal-looking sprial system. 3. What are the distinctive observations that distinguish quasars from other objects? You should include redshift, spectrum, brightness variations. quasar Star-like radio source with an observed redshift that indicates extremely large distance from Earth. Quasar host galaxies are hard to see because they are so much fainter than the quasar itself. Quasar spectra were understood when it was discovered that their radiation is hydrogen by an unexpectedly large amount. Quasars are also known as quasi-stellar objects because of their unimpressive appearance at visible wavelengths. quasars now known is that their spectra all show large redshifts, ranging from 0.06 (that is, a 6 percent increase in wavelength) 4. What are the characteristics of quasars inferred from their observations distance, luminosity, size, energy source, their true nature? The distance to a quasar in light-years is not simply equal to the time in years since the quasar emitted the light we see because of the expanding of the universe. The fact that a typical quasar would consume an entire galaxy’s worth of mass in 10 billion years suggests that quasar lifetimes are relatively 10 billion years old. Quasar host galaxies are hard to see because they are so much fainter than the quasar itself. 5. What are several theories for quasars? Evaluate them on the basis of the observational evidence. Quasars are also known as quasi-stellar objects because of their unimpressive appearance at visible wavelengths. quasars now known is that their spectra all show large redshifts, ranging from 0.06 (that is, a 6 percent increase in wavelength). 6. What is meant by a gravitational lens? What can astronomers learn from studying lensed quasars? The idea behind gravitational lensing in which a disc-shaped galaxy produces three images of a more distant quasar as its light passes through the galaxy. gravitational lensing The effect induced on the image of a distant object by a massive foreground object. Light from the distant object is bent into two or more separate images. 7. What is the single model that gives a unifying picture of the various radio-emitting galaxies? Lobe radio galaxies emit radio radiation from regions that are typically much more than 10 times in size than the visible galaxy. The radio lobes of lobe radio galaxies are truly enormous. From end to end, an entire lobe radio galaxy typically is more than 10 times the size of the Milky Way Galaxy, comparable in size to the entire Local Group. APPLYING YOUR KNOWLEDGE 1. Hypothesis: Quasars are at cosmological distances. Question: What evidence have astronomers collected in favor of this hypothesis? What types of evidence do some astronomers present against it? How are the spectra of distant quasars used to probe the space between us and them? In addition to their own strongly redshifted spectra, many quasars also show additional absorption features that are redshifted by substantially less than the lines from the quasar itself. For example, the quasar PHL 938 has an emission-line redshift of 1.955, placing it at a distance of some 3400 Mpc, but it also shows absorption lines having redshifts of just 0.613. These are interpreted as arising from intervening gas that is much closer to us (only about 1700 Mpc away) than the quasar itself. Most probably this gas is part of an otherwise invisible galaxy lying along the line of sight, affording astronomers an important means of probing previously undetected parts of the universe. 2. How do astronomers infer the size of a quasar's emitting region from observations of the variability of its brightness? Despite their unimpressive opticalappearance, the large distances implied byquasar redshifts mean that these faint "stars" are in fact the brightest known objects in the universe! 3C 273, for example, has a luminosity of about 1040 W. More generally, quasars range in luminosity from around 1038 W-about the same as the brightest radio galaxies-up to nearly 1042 W. A value of 1040 W, comparable to 20 trillion Suns or 1000 Milky Way Galaxies, is fairly typical. 3. Summarize the evidence that active galaxies contain massive black holes in their nuclei. As a young galaxy developed and its central black hole used up its fuel, the luminosity of the nucleus diminished. While still active, this galaxy no longer completely overwhelmed the emission from the surrounding stars. The result was an active galaxy-either radio or Seyfert-still emitting a lot of energy, but now with a definite "stellar" component in its spectrum. The central activity continued to decline. Eventually, only the surrounding galaxy could be seen-a normal galaxy, like the majority of those we now see around us. Today, the black holes lie dormant in galactic nuclei, producing only a relative trickle of radiation. Occasionally, two normal galaxies may interact with one another, causing a flood of new fuel to be directed toward the central black hole of one or both. The engine starts up again for a while, giving rise to the nearby active galaxies we observe. Should this picture be correct-and the confirmation of host galaxies surrounding many quasars lends strong support to this view-then many normal galaxies, including perhaps our own Milky Way Galaxy, were once brilliant quasars. Perhaps some alien astronomer, thousands of megaparsecs away, is at this very moment observing our Galaxy-seeing it as it was billions of years ago-and is commenting on its enormous luminosity, nonstellar spectrum, and high-speed jets, and wondering what exotic physical process could possibly account for its violent activity! We can construct the following (speculative) scenario for the evolution of galaxies in the universe. Galaxies began to form some 9-10 billion years ago (corresponding to a redshift of 5, the upper limit on the measured redshifts of known quasars-see Table 16.1). The first massive stars to form in a galaxy may have given rise to many stellar-mass black holes which sank to the galactic center and merged into a supermassive black hole there. Alternatively, the supermassive hole may have formed directly by gravitational collapse of the galaxy’s dense central regions. Whatever their precise origin, large black holes appeared at the centers of many galaxies at a time when there was still plenty of fuel available to power them, resulting in many highly luminous quasars. The brightest quasars-the ones we now see from Earth-were those with the greatest fuel supply. 4. What effects do uncertainty in the value of the Hubble constant have on our understanding of quasars? Of course, because of Hubble’s law, redshift and distance are equivalent to one another. However, redshift is the preferred quantity because it is a directly observable property of an object, whereas distance is derived from redshift using Hubble’s constant, whose value is not accurately known. In the next chapter, we will see another reason why astronomers favor the use of redshift in studies of the cosmos. Using Hubble’s law, we can derive the distance to a remote object simply by measuring the object’s recessional velocity and dividing by Hubble’s constant. (Notice, however, that the uncertainty in Hubble’s constant translates directly into a similar uncertainty in the distance determined by this method.) Using Hubble’s law in this way tops our inverted pyramid of distance-measurement techniques. Hubble’s constant H0 to be 65 km/s/Mpc. 5. Consider four classes of objects: normal galaxies like the Milky Way, Seyfert galaxies, radio galaxies and quasars. Arrange these objects in order of increasing energy output. Sketch a diagram that shows the relationship. normal galaxies like the Milky Way, Seyfert galaxies, radio galaxies and quasars >6. The following are observations for a fictitious quasar: redshift is 0.6 the speed of light: observed brightness is 10 -17 that of the Sun. Compute the distance to the quasar and its luminosity in terms both of the Sun and of the Milky Way galaxy. >7. Suppose astronomers observe hydrogen lines in the spectrum of a quasar to have three components at wavelengths of 5200 A, 5201 A, and 5205 A. The usual wavelength is at 4861 A. If the three components are due to absorption along the line of sight to the quasar, what is the distance between each of the absorbing clouds? What assumption are you implicitly making in obtaining your answer? >8. Consider a simplified galaxy having only 10 stars. If F., is the force between stars numbered 1 and 2, write down all the other forces that a computer program must consider in analyzing the movements of stars in a collision. Inquiry Because quasar redshifts are large the usual Doppler shift formula must be replaced by one that accounts for the theory of relativity. If Z = AA/A the expression to find the velocity becomes V = (1 + Z)Z - 1. C (1 + Z)2 + 1. Chapter 23 Page 546 SUMMARY QUESTIONS 1. What is the crucial role of measurement and observa- tion in the definition of the universe? To find out how faraway planets, and stars are, and the measurements give information as to how big in size the universe is. One way to measure the distance is Parallax measurements of the distances to the stars nearest Earth use as a baseline. The distances to the nearest stars can be measured using parallax Observation of the universe is seeing many galaxies, objects, planets, stars. 2. What is the interpretation of Hubble's redshift observations? cosmological redshift relate to the expansion of the universe? osmological Redshift As the universe expands, photons of radiation are stretched in wavelength, giving rise to the cosmological redshift. These huge speeds mean that neither of these two objects can possibly be members of our Galaxy. Applying Hubble’s law with our adopted value of H0 = 65 km/s/Mpc, we obtain distances of 660 Mpc for 3C 273 and 1340 Mpc for 3C 48. More Precisely 16-1 discusses in more detail how these distances are determined and what they mean. Clearly not stars (because of such enormous redshifts), these objects became known as quasi-stellar radio sources (quasi-stellar means "starlike"), or quasars. Quasars can spectral lines of hydrogen redshifted. 3. What are the various observable differences to be expected between a steady-state universe, a big- bang universe that expands forever, and a big-bang universe that eventually collapses on itself? Your discussion should include observations of changes in density and expansion velocity, and the 3-K back- ground radiation. What are the difficulties in making observations of each? The Steady State model of the Universe was proposed in 1948 by Bondi and Gold and by Hoyle. Bondi and Gold adopted the "Perfect Cosmological Principle", and added the assumption that the Universe was the same at all times to homogeneity (the same in all places) and isotropy (the same in all directions). At the time the Steady State model was proposed, the Big Bang model was in trouble because the value of the Hubble constant was clearly bigger than the inverse of the age of the Universe. [Sound familiar?] If the Universe is the same at all times, the value of the Hubble constant must really be constant, so v = dD/dt = HD has an exponential solution and the scale factor varies like a(t) = exp(H(to-t)) Furthermore, since the radius of curvature of the Universe can not change, but must expand, the radius has to be infinite. The Steady State model has flat spatial sections like the critical density Big Bang model. Since the expansion of the Universe spreads the existing matter over a larger and larger volume, the density stays constant, the Steady State model requires continuous creation of matter. The average age of matter in the Steady State model is = 1/(3*Ho) but some galaxies are much older than the average, so the age of the globular clusters can be accomodated if the Milky Way is older than the average. The space-time diagram below shows the Steady State model: Hubble’s law therefore implies that, at some time in the past-15 billion years ago, according to the foregoing simple calculation-all the galaxies in the universe lay right on top of one another. In fact, astronomers believe that everything in the universe-matter and radiation alike-was confined to a single point at that instant. Then the point exploded, flying apart at high speeds. The present locations and velocities of the galaxies are a direct consequence of that primordial blast. This gargantuan explosion, involving everything in the cosmos, is known as the Big Bang. It marked the beginning of the universe. Expanding very fast in fast speeds. A density wave made up of two spiral arms is moving through the Galactic disk. At the 8-kpc radius of the Sun’s orbit around the Galactic center, the wave’s speed is 120 km/s, and the Galactic rotation speed is 220 km/s. Calculate how many times the Sun has passed through a spiral arm since the Sun formed 4.6 billion years ago. cosmic microwave background The almost perfectly isotropic radio signal that is the electro-magnetic remnant of the Big Bang. the Milky Way’s emission at microwave wavelengths. In their data, they noticed a bothersome background "hiss"-a little like the background static on an AM radio station. Regardless of where and when they pointed their antenna, the hiss persisted. Never diminishing or intensifying, the weak signal was detectable at any time of the day and on any day of the year, apparently filling all of space. the origin of the mysterious static was nothing less than the fiery creation of the universe itself. The radio hiss detected is now known as the cosmic microwave background. 4. What are the main events during the expansion of the universe? What were the conditions prevailing when each event occurred? What evidence of the events can be observed today? Big Bang as simply an enormous explosion that spewed matter out into space, ultimately to form the galaxies we see, then the foregoing reasoning would be quite correct. The universe would have a center and an edge, and the cosmological principle would not apply. The Big Bang was not an explosion in an otherwise featureless, empty universe. The only way that we can have Hubble’s law and retain the cosmological principle is to realize that the Big Bang involved the entire universe-not just the matter and radiation within it, but the universe itself. In other words, the galaxies are not flying apart into the rest of the universe. The universe itself is expanding. Like raisins in a loaf of raisin bread that move apart as the bread expands in an oven, the galaxies are just along for the ride. Hubble’s law describes the expansion of the universe itself. Apart from small scale individual random motions, galaxies are not moving with respect to the fabric of space. The component of the galaxies’ motion that makes up the Hubble flow is really an expansion of space itself. The expanding universe remains homogeneous at all times. There is no "empty space" beyond the galaxies into which they rush. At the time of the Big Bang, the galaxies did not reside at a point located at some well-defined place within the universe. The entire universe was a point. The Big Bang happened everywhere at once. 5. Why must elements heavier than helium have been created in the stars rather than during the big bang? The temperatures are very hot inside of the bright stars. Nuclear burning fuel process inside of the stars. 6. What is the future of the universe? How may we decide among the various possible outcomes? The Universe may collapse very suddenly. The Universe maybe expanding forever. 7. How is the shape of the universe related to its history and the amount of mass it contains? What are some geometrical analogies to various types of universes? Cosmic Inflation During the period of inflation the universe expanded enormously in a very short time. Afterward, it resumed its earlier "normal" expansion rate, except that now the size of the cosmos was about 1050 times bigger than it was before inflation. During inflation, the universe swelled in size by a factor of about 1050. 8. What is the 3-K background radiation? Describe it both from the observational and theoretical view- points. What was the significance of the observations made by COBE? Radiation-Matter Decoupling When atoms formed, the universe became virtually transparent to radiation. observations of the cosmic background radiation allow us to study conditions in the universe around a time at a redshift of 1500, when the temperature dropped below about 4500 K. Although dark matter does not interact directly with photons, the background radiation is influenced slightly by the gravity of the growing dark clumps This causes a slight gravitational redshift in the background radiation that varies from place to place depending on the dark-matter density. As a result, dark-matter models predict that there should be tiny "ripples" in the microwave background-temperature variations of only a few parts per million from place to place on the sky. In 1992, after almost two years of careful observation, the COBE team announced that the expected ripples had been detected. The temperature variations are tiny-only 30-40 millionths of a kelvin from place to place in the sky-but they are there. The COBE results are displayed as a temperature map of the microwave sky in Figure 17.20. The ripples seen by COBE, combined with computer simulations such as that shown in Figure 17.19, predict present-day structure that is quite consistent with the superclusters, voids, filaments and Great Walls we actually see around us. Detailed analysis of the ripples also supports the key prediction of inflation theory-that the universe is of exactly critical density and hence spatially flat. For these reasons, most cosmologists now regard the COBE observations as striking confirmation of a central prediction of dark-matter theory. They rank alongside the discovery of the microwave background itself in terms of their importance to the field of cosmology. 9. What are the observations astronomers have made that lend credence to the big-bang theory? Big Bang Event that cosmologists consider the beginning of the universe, in which all matter and radiation in the entire universe came into being. 10. What is the Halley-Olbers paradox? What are various ideas considered to resolve it successfully? Olber's paradox A thought experiment suggesting that if the universe were homogeneous, infinite, and unchanging, the entire night sky would be as bright as the surface of the Sun. APPLYING YOUR KNOWLEDGE 1. What influence would the aging of galaxies have on observations of galaxy counts at greater and greater distances? Would such aging tend to make the uni- verse seem to decelerate at a greater or lesser rate than it actually does? The universe may decelerate over time if the expansion of the universe is decelerating. The galaxies at greater distances maybe very new galaxies in the process of forming or have recently been formed, or have been around for a long time. 2. Summarize the predictions the big-bang theory makes. What do observations have to say about each of these predictions? 1.) Number density of galaxies is greater in the past -- observed 2.) Microwave background radiation at 3 K -- observed as predicted 3.) Isotropy of background radiation -- observed as predicted 4.) Abundance of H, He, and deuterium -- observed as predicted 5.) Hubble Constant decreases with time -- uncertain because of large uncertainties About 15 billion years ago a tremendous explosion started the expansion of the universe. This explosion is known as the Big Bang. At the point of this event all of the matter and energy of space was contained at one point. What exisisted prior to this event is completely unknown and is a matter of pure speculation. This occurance was not a conventional explosion but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Big Bang actually consisted of an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The galaxies were not all clumped together, but rather the Big Bang lay the foundations for the universe. The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding. He discovered that a galaxys velocity is proportional to its distance. Galaxies that are twice as far from us move twice as fast. Another consequence is that the universe is expanding in every direction. This observation means that it has taken every galaxy the same amount of time to move from a common starting position to its current position. Just as the Big Bang provided for the foundation of the universe, Hubbles observations provided for the foundation of the Big Bang theory. Since the Big Bang, the universe has been continuously expanding and, there has been more and more distance between clusters of galaxies. This phenomenon of galaxies moving farther away from each other is known as the red shift. As light from distant galaxies approach earth there is an increase of space between earth and the galaxy, which leads to wavelengths being stretched. In addition to the understanding of the velocity of galaxies emanating from a single point, there is further evidence for the Big Bang. In 1964, two astronomers, Arno Penzias and Robert Wilson, in an attempt to detect microwaves from outer space, inadvertently discovered a noise of extraterrestrial origin. The noise did not seem to emanate from one location but instead, it came from all directions at once. It became obvious that what they heard was radiation from the farthest reaches of the universe which had been left over from the Big Bang. This discovery of the radioactive aftermath of the initial explosion lent much credence to the Big Bang theory. The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions. In 1927, the Belgian priest Georges Lemaître was the first to propose that the universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant nebulas by astronomers to a model of the universe based on relativity. Years later, Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance. The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson. Although the Big Bang Theory is widely accepted, it probably will never be proved; consequentially, leaving a number of tough, unanswered questions. 3. The wavelength of a photon emitted in a transition is proportional to the velocity of light. Let's speculate that as light travel through the universe it becomes tired - that is, it loses energy. Predict the conse- quences of tired light on our observations of both distant and nearby galaxies. Were light to become tired and loose energy as it traversed space, its wavelength would decrease as it travels. The farther away an object is, the greater the time over which the light would lose energy. With such a concept, which has no basis in fact, radiation from distant objects would be redshifted, but it would not be caused by a general expansion of the Universe. Tired light models invoke a gradual energy loss by photons as they travel through the cosmos to produce the redshift-distance law. This has three main problems: There is no known interaction that can degrade a photon's energy without also changing its momentum, which leads to a blurring of distant objects which is not observed. The Compton shift in particular does not work. The tired light model does not predict the observed time dilation of high redshift supernova light curves. This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1. The plot shown above gives the factor by which the supernova light curve has been dilated for five supernova versus the redshift and represents the data available in 1998. In 2001 Goldhaber and the Supernova Cosmology Project published results of a time dilation analysis of 60 supernovae. A plot of their width factor w versus the redshift z is shown below. If the redshift were due to a tired light effect, the width of a supernova light curve would be independent of the redshift, as shown by the red horizontal line. 4. The wavelength of a photon emitted in a transition is inversely proportional to the mass of an electron. Let's speculate that the mass of an electron increases with time. Predict the consequences of increasing electron mass on our observations of the spectra of both distant and nearby galaxies. at room temperature, for every 1,000,000,000 atoms at the ground level (E1), there are 4 atoms in the excited state (E2). the photon with the longer wavelength is the one with the lower frequency, ie with lower energy, which is the photon emitted in the transition from n=4 to n=3. 5. Suppose that rather than beginning from a strongly condensed condition, the universe began as a ball of gas having the size it has today. Suppose, further, that matter was spread out uniformly except for a few local irregularities and with zero motion that is, it was static. Describe the subsequent history of this universe and the reasons for your description. Planets maybe stationary not moving around a star. At any given location, the only materials to condense out were those able to survive the temperature there. The composition of the material that could condense out at any given distance from the Sun ultimately determined the type of planet that formed there. formed under cold conditions out of low-density, icy material. 6. Suppose the velocity-distance relation for the uni- verse were as given in Figure 23-21. Explain the consequences of this velocity-distance relation. Hubble's law Law that relates the observed velocity of recession of a galaxy to its distance from us. The velocity of recession of a galaxy is directly proportional to its distance away. 7. Creationists argue that because astronomers observe the mass within galaxy clusters to be insufficient to hold the clusters together, such clusters can exist only if the universe is considerably younger than astronomers say. How might you respond to such an argument? The Hubble Constant can be used to determine the intrinsic brightness and masses of stars in nearby galaxies, examine those same properties in more distant galaxies and galaxy clusters, deduce the amount of dark matter present in the universe, obtain the scale size of faraway galaxy clusters, and serve as a test for theoretical cosmological models. In the short time we have remaining in this quarter, we will enter this debate as we work to determine our value for the Hubble constant. gravitational influence on something else. This principle applies to planets, stars, galaxies, and even clusters of galaxies-very different objects 8. In Chapter 21 we saw that galaxy masses could be found from studies of rotation curves for spiral galaxies and velocity dispersion for elliptical galaxies. If galaxies containing massive black holes were studied with these techniques, would the computed masses include the masses of the black holes or would their masses be neglected? Explain. Would hypothesizing black holes at the centers of galaxies bring the universe's overall density above the cri- tical density? There masses maybe neglected if the galaxies had those massive black holes. Due to the elliptical galaxies, and how they were structured. The black holes if they were at the centers of galaxies would certainy have the density above the critical density due to there location. 9. Explain the Hubble law using points along a line, in a manner similar to that used in the raisin bread analogy. __.__.__.__.__.__.__.__-__.__.__.__.__.__.__.__. Your Hubble constant is 75 km/sec/Mpc, then 1/75 = 0.0133 = 1.33 x 10 -2 (1.33 x 10 -2 ) x (3.09 x 10 19 ) = 4.12 x 10 17 (4.12 x 10 17 ) divided by (3.16 x 10 7 ) = 1.3 x 10 10 This is 1.3 x 10 10 years, or 13 x 10 9 years, or 13 billion years. >10. Compute how far a photon could travel over the age of the universe. speed of light The fastest possible speed, according to the currently known laws of physics. Electromagnetic radiation exists in the form of waves or photons moving at the speed of light. We know the speed of light, 2.9979 x 10^8 m/s, and so if we have either the wavelength or the frequency, we can calculate the other value. For example (and let’s stick with those electron jumps that result in photons in the visible part of the spectrum for now), the jump from energy level 3 to 2 results in a line at 656.3 nm. What is the frequency of this photon? How does the frequency of this photon compare to that of a photon with a wavelength of 364.6 nm >11. Estimate the total number of atoms in the universe! Hint: To solve this problem you need to make a number of educated guesses. No part of our Galaxy is truly devoid of matter, although the density of the interstellar medium is extremely low. Overall, the gas averages roughly 106 atoms per cubic meter-just one atom per cubic centimeter. >12. Compute the maximum age of the universe in years for values of H = 15 km/sec/Mly and 25 km/sec/ Mly. 25 + 15 = 40 FIGURE 23-21. Shows a hypothetical velocity-distance relation. Radial velocity is on left side Distance is underneath and a blue line starts out from right hand side and travels uphill to upper left corner. + 0 CHAPTER 1 Sample Quiz #1 1. About how long would it take light to reach the Earth from the center of our Galaxy. A. between 1 and 10 minutes B. between 1 and 10 years C. between 10+4 and 10+5 years D. between 10+6 and 10+7 years E. between 10+8 and 10+9 years 2. The diameter of the Earth is about 13,000 km, while the diameter of the Earth's orbit is about 300,000,000 km. The second figure is how many orders of magnitude larger than the first? A.1 B.2 C.3 D.4 E.5 3. Multiply 1.4 x 10-7 by 4 x 10+2 Answer = page 7 4. Order the following objects by size, from smallest to largest: A. Earth B. Jupiter C. Betelgeuse D. the Sun E. Saturn 5. The age of the Universe is about A. 10,000 years D. 100,000,000 years B. 100,000 years E. 10,000,000,000 years C. 1,000,000 years 6. Which of the statements below is incorrect? A. 1 AU is approximately 100 times the diameter of the Sun. B. The Sun's diameter is approximately 10,000 times that of the Earth. C. Pluto is 40 times farther from the Sun than the Earth is. D. The average distance between stars in the Galaxy is about 5 LY. E. Our Galaxy is approximately 100,000 LY in its longest dimension. Chapter 1 Sample Quiz #2 7. Compare the numbers 3,000,000 and 4,000 as to their relative orders of magnitude. A. 3,000,000 is 3 orders of magnitude larger than 4,000 B. 3,000,000 is 750 orders of magnitude larger than 4,000 C. 3,000,000 is 1000 orders of magnitude larger than 4,000 D. 3,000,000 is approximately the same order of magnitude as 4,000 E. the two numbers are 12,000,000,000 orders of magnitude different 8. All the giant planets in the solar system have ring systems A) True B) False 9. The Astronomical Unit (AU) is defined as A. the longest dimension of the solar system B. the distance between the earth and the sun C. the time it takes light to cross the solar system D. the average distance between stars in the galaxy E. a variable quantity, depending upon what is being measured 10. Compared to the Earth's diameter, the diameter of Jupiter is ___ order(s) of magnitude ___ A. 2, larger B. 1, larger C. of the same order of magnitude D. 1, smaller E. 2, smaller 11. Multiply 1.7 x 10 17 by 2 x 10-5 Answer= 12. Compare the number of stars in a galaxy (in order of magnitude) to the number of stars in one of the globular clusters in our galaxy. It would be _____ orders of magnitude(s) more. A. 1 B. 2 C. 3 D. 4 E. 5 F. 6 Answers: 1)C 2)D 3) 5.6 x10-5 4. AEBDC 5) E 6)B 7)A 8)A 9) B 10) B 11) 3.4 x 10 12 12)F Page 8 Test Yourself Chapter 2 Sample Quiz 1) Science is a quest for a) absolute truth b) supernatural explanations c) models that make better predictions d) all of the above e) none of the above 2) Standing in your front yard at night, the most intense source of radiation you are exposed to would be a) the planet Mars b) the planet Jupiter c) the brightest star, Sirius d) the porch light page 11 3) If the universe were 5,000 years old, how far could we see out into space? a) 5,000 LY b) 5 billion LY c) there should be no relation between age and this distance d) there should be no limit on how far we can see e) there is not enough information to answer the question 4) Scientists attempt to understand the real world primarily by A. Observing, then devising theories that explain the data and predict new observations. B. rejecting observations which fail to agree with established theories. C. constructing a new theory to explain each new observation. D. organizing scientific revolutions. E. predicting the consequences of accepted physical laws. 5) Astronomers are able to investigate the early stages in the evolution of the Universe by making use of the fact that A. the galaxies are very old. B. radioactive materials take a long time to decay. C. light travels at a finite speed. D. the Earth is about 5 billion years old. E. stars evolve on time scales of millions to billions of years. 6) The greatest difficulty faced by astronomers is that A. we cannot set up stellar situations in the laboratory, so we have no way to figure out the physics that is going on. B. we cannot tell how far away things really are. C. astronomical objects have very long lifetimes, in comparison to the amount of time we have been seriously observing them. D. light travels at a finite speed, so we have to wait for all the data we need to arrive. E. the scientific method cannot be fully applied to astronomy because we cannot control and experiment on the stars. 7) Which of the following statements correctly expresses the relationship between theory and observation in astronomy? A. theory is more important, since the Universe presents so many possibilities B. observation is more important, as there is such a multiplicity of phenomena in the Universe C. theory and observation are equally important, and neither forms a complete scientific method by itself. D. theory serves mostly to summarize and organize the data gathered by observers with telescopes. E. astronomers collect observations primarily to confirm or deny the theoretical possibilities that have been formulated. TEST ANSWERS: 1) c 2) d 3) a 4) a 5) c 6) c 7) c page 12 Chapter 3 Sample Quiz #1 1. The graph on the right shows the relationship between angle and yard- stick reading obtained by a student. What angle corresponds to a yardstick reading of 20"? A. 2 0 B. 2.5 0 C. 3 0 D. 3.5 0 E. 4 0 2. Which of the following are sources of systematic errors that could affect the quadrant reading? A. unsteadiness in the hand holding the quadrant B. a steady wind blowing towards the observer C. locating the tack holding the string in the wrong place D. both A and B E. both B and C 3. Which of the following are sources of random errors that could affect the cross-staff reading. A. not always holding the end of the cross-staff at the same point on your cheek. B. using a yardstick with incorrectly marked graduations. C. using a bent ruler to determine the angle from the nomogram. D. both A and B E. both B and C page 14 4. The diameter of the Earth is about 13,000 km. About how large would it appear to an astronaut who was 52,000 km from the Earth? A. 0.25 0 B. 1 0 C. 2.5 0 D. 5 0 E. 15 0 5. Define what is meant by the altitude of a celestial object in the sky. 6. One degree equals how many seconds of arc? A. 360 B. 60 C. 365 D. 3600 E. 3600000 Chapter 3 Sample Quiz #2 7. A student measures the angle between two stars. Five measurements are made: 15 0, 14 0, 15 0, 16 0, 16 0. The student should report the measurement as A. 15.2 0 (+ or -) 0.5 0 B. 15.2 0 (+ or -) 1 0 C. 15.2 0 (+ or -) 1.5 0 D. 15.2 0 (+ or -) 2 0 E. 15.2 0 (+ or -) 2.5 0 8. Which of the following changes would not make for more accurate angular measurements with a cross-staff? A. precision ruling the markings on the stick B. reading the setting of the cross-piece with a magnifier C. making every dimension of the cross-staff 10 times larger D. making the nomograph 10 times larger E. all of the above would make the process more accurate 9. Which of the following statements correctly describes the percentage errors that result when altitudes are measured with the quadrant? A. It measures all angles to about the same percentage error B. It gives a smaller percentage error for large angles. C. It gives a smaller percentage error for small angles. D. The percentage errors are random. 10. When you sight the distant horizon with your quadrant, what value does it read? 11. If the Sun's actual diameter is 1.4 million km, and its distance from the Earth is 150 million km, what is its angular diameter? A. 0.53 0 B. 107 0 C. 210 million million D. cannot be answered from the information given. 12. In measuring angles and angular sizes by using the hand method approximately what angle is subtended by holding your fist at arm's length and sighting it. A. 1 0 B. 2 0 C. 10 0 D. 20 0 E. People's hands differ so much that this question cannot be answered even approximately. Answers: 1)b 2)e 3)d 4)e 5) angular distance above the horizon 6)d 7)b 8)e 9)b 10) zero 11)a 12)c page 15 Set up the globe for an observer located at the north pole of the Earth. 1) Set the Sun at its ecliptic position for June and rotate the celestial globe through an entire 24- hour day at the north pole. Describe how the Sun will appear to move. 2) Set the Sun at its position for Sept. 23. How does it move during the course of a 24-hour day? 3) Set the Sun for December. How does it behave during a 24-hour day. How do the stars move? Now set the celestial globe up for an equatorial observer. 4) Set up the Sun on its vernal equinox position (late March, crossing the celestial equator from south to north). Where on the horizon does the Sun rise, and where does it set? 5) Set the Sun on its late June position. Where does the Sun rise and where does it set? 6) Set the Sun for late December. Where does the Sun rise and where does it set? 7) How do the lengths of night and day compare at different times of the year on the equator? 8) At what angle with respect to the horizon do stars rise and set? Now set up the celestial globe for your latitude on Earth. 9) Set the Sun for late June. Where does the Sun rise and where does it set? How high in the sky does it get at mid-day? One hour after sunset, what constellations are highest in the sky? Set the Sun for the middle of the night. What constellations are highest in the sky? 10) Set the Sun for late December. Where does the Sun rise and where does it set? How high in the sky does it get at mid-day? How does the length of the day compare to its length in June? One hour after sunset, what constellations are highest in the sky? Where are the constellations that were high in the sk for question 9? 11) At what angle with respect to the horizon do the stars rise and set at your latitude? page 18 CELESTIAL GLOBE ACTIVITY Answer Sheet NAME: At the North Pole: 1) June. How does the Sun move? 2) September. How does the Sun move? 3) December. How does the Sun move? How do the stars move? At the Equator: 4) Late March. Where does the Sun rise and set? 5) Late June. Where does the Sun rise and set? 6) Late December. Where does the Sun rise and set? 7) Relative lengths of night and day during the year? 8) Angle at which stars rise and set with respect to the horizon? At Your Latitude (which is approximately what?) 9) June: where does the Sun rise and set, and how high does it get at mid-day? page 19 What constellations are high in the sky one hour after sunset? At the middle of the night? 10) December: where does the Sun rise and set, and how high does it get at mid-day? How does the length of the day compare to the day in June? Why? Where are the constellations that were high in the sky during the June evening? What constellations are high in the sky one hour after sunset? 11) At what angle do stars rise and set with respect to the horizon? page 20 Mail Box Bombs Mail Box Bombs by the Jolly Roger (1) Two litre bottle of chlorine (must contain sodium hypochlorate) Small amount of sugar Small amount of water Mix all three of these in equal amounts to fill about 1/10 of the bottle. Screw on the lid and place in a mailbox. It's hard to believe that such a small explosion will literally rip the mailbox in half and send it 20 feet into the air Fertilizer Bomb How to make a fertilizer bomb Ingredients: - Newspaper - Fertilizer (the chemical kind, GREEN THUMB or ORCHO) or Shultz - Cotton - Diesel fuel Make a pouch out of the newspaper and put some fertilizer in it. Then put cotton on top. Soak the cotton with fuel. Then light and run like you have never ran before! This blows up 500 square feet so don't do it in an alley! for the April 19, 1995, bombing of the Oklahoma City federal building that killed 168 people and injured hundreds of others. Top Stories - AP Witness: Nichols Tested Bomb Ingredients Tue May 13, 6:56 AM ET OKLAHOMA CITY - Timothy McVeigh (news - web sites) and bombing conspirator Terry Nichols detonated explosives in the Arizona desert and experimented with ingredients that were later used in the Oklahoma City bombing, McVeigh's close friend testified. Michael Fortier, testifying at a preliminary hearing for Terry Nichols, also said McVeigh had worked out plans for the Oklahoma City bombing six months before a bomb ripped through the federal building, killing 168 people. Fortier said McVeigh told him in October 1994 that he and Nichols planned to blow up the Alfred P. Murrah Federal Building (news - web sites). He discussed how he would take ammonium nitrate and fuel and mix it up and put it in 55-gallon drums, Fortier testified Monday. assemble the bomb's components raise money and assembled components of the bomb that was detonated outside the federal building. Nichols was at home in Kansas the day the bomb exploded. But prosecutors said he helped McVeigh deliver a getaway car to Oklahoma City and worked with McVeigh to pack the 4,000-pound bomb inside the truck the day before the bombing. Tim once told Pringle that you could make a bomb out of nitro and fertilizer. 08.??.94-late Sept. 1994 Tim and Terry started buying fertilizer. Terry bought two bags from Burns, KS. Tim bought eight bags in a town east of Manhattan on HWY 163. McVeigh bought ten bags in McPherson. Terry bought 40 bags in McPherson. Tim also bought some in a town 20 miles south of McPherson west of I-35 at their co-op During his employment at TruValue Hardware in Kingman, Tim bought two 75 pound bags of fertilizer from Mike Black. On December 31, 1995 Tim said he only sold 100 kilogram bags of ammonium nitrate. Tim purchased 10 bags of fertilizer from the Mid-Kansas Coop in McPherson, KS 09.30.94 McVeigh and Nichols purchased forty fifty-pound bags of ammonium nitrate in McPherson, Kansas Forty fifty-pound bags of fertilizer purchased from Mid-Kansas Coop in McPherson, KS 09.30.94 Terry bought forty bags, 2,000 lbs. of fertilizer, from McPherson, Kansas before they left. Terry bought 40 more bags from McPherson, Kansas. Prior to leaving Marion, Tim bought eight bags in Manhattan, one bag in Burns and six bags in a town below McPherson. McVeigh made telephone calls in an attempt to obtain detonation cord and racing fuel. September-October 94 McVeigh to purchase three drums of nitromethane at $950 each from V.P. Racing which was located south of Dallas. blasting caps and det cord Tim and Terry camped at Geary Lake Park for approximately two weeks. 299 (1-1/2 by 6 inch) sticks of dynamite, 544 electric blasting caps and 93 non-electric blasting caps 350 pounds of blasting caps The blasting caps and gelatin 350 pounds of gel, 600 blasting caps and Primadet cord. 10.20.94 Tim and Terry drove through Oklahoma City headed to buy nitromethane at a race track in Dallas. They drove by the Murrah Building, got out, walked around and timed the walking distance from the building to where Tim would be when the bomb went off. McVeigh had called model shops in search of nitromethane fuel, commonly used in auto racing. He found a source on the Funny Car Racing Circuit by hanging around pit areas. He was offered 55-gallon drums of nitromethane for $1,000 a drum from a source in Manhattan, KS. The main office of V.P. Racing was in Manhattan, KS. McVeigh and Nichols bought the nitromethane from a V.P. Racing delivery truck located in Dallas, TX It took them awhile to find the race track. They finally found it in Winston Coveston (?). Tim let Terry out of the truck before they got to the track. Tim bought three drums of nitromethane from a man for $900 [33] a drum, and paid cash. [34] The man did not ask for a name. They returned to Kansas and unloaded all the fuel into the storage shed in Herington. They bought six black plastic barrels with full take-off lids on the top, six white plastic ones with the little lids you take off on the top, and one blue one. The white ones were free at the Hillsboro Milk Co-op and the black ones cost $12. each. The blue one came from a plastics manufacturing company next to the Council Grove store. 10.2?.94 Tim and Fortier tested a small explosives mixture. They walked for 2 miles and used jet fuel and a little bit of fertilizer in a one gallon gatarade container. He wanted to make sure that the cap would set it off. (Hankins memo dated 5.10.95). Tim exploded a Gatorade bottle I believe in Arizona with a mixture of nitro and ammonium nitrate with a cap. fuel oil to nitromethane That huge piece of twisted metal had been at the center of the bomb. The force of the explosion had sent it whirling through the air for about 200 yards or more. That piece of twisted metal was the rear axle of a Ryder truck. It was a Ryder truck that Timothy McVeigh had rented two days before in Kansas. we will have proven to you beyond any reasonable doubt that Timothy McVeigh destroyed the Murrah Building and killed people inside by means of a huge fertilizer bomb built inside a Ryder truck. You'll hear that he and Terry Nichols had experimented with small explosives on Nichols' farm in Michigan. Later our evidence will prove that McVeigh graduated to larger bombs, and you'll hear about an incident that occurred just one year before the bombing in a desert in Arizona where he made and detonated a pipe bomb. He placed it near a large boulder in the desert, and he ran away as the pipe bomb exploded and cracked the boulder. You will see that he also educated himself about how to build bombs, particularly truck bombs, using ammonium nitrate fertilizer and some sort of fuel oil. And we'll explain to you how you can make a bomb from fertilizer and fuel oil, and of course that's consistent with the type of destructive device that was used in Oklahoma City. So The Turner Diaries was one of his favorite books where the heroes blow up the federal building with a homemade truck bomb, but he also obtained what was really a cookbook on how to make bombs. He order the book through the mail, we will show you; and the book is called Home Made C4. C4 is a type explosive. Some of you with military background know that. This book provides essentially a step-by-step recipe as to how to put together your own fertilizer fuel-based bomb. And the book even provides helpful hints as to where to acquire the various ingredients, the components. It describes how to build a powerful bomb, and it does so in simple, understandable terms. In fact, it shows how unbelievably simple it is to make a hugely, hugely powerful bomb. McVeigh ordered and received the book from Paladin Press in the spring of 1993. The day that he selected for the bombing also has significance. He selected April 19th. Of course, first, that was the anniversary of Waco, and he wanted to, as he said, avenge death that occurred at Waco; and second, April 19th a couple of centuries ago, in 1775, that's the day that the American Revolution is reported to have begun. That's the day that the opening shot was fired in Concord/Lexington. The day is known as Liberty Day. Turner Diaries and this book Homemade C4, the bomb-making cookbook, told him to where to look. The best place to get ammonium nitrate fertilizer, the book said, was at a farm supply store, and the best place to get nitromethane racing fuel, which you would mix with the fertilizer, was at a raceway. They got 4,000 pounds -- that's 2 tons of ammonium nitrate fertilizer. They bought it at a farm supply store in central Kansas where Nichols was living at the time and where McVeigh visited him. This was in the fall of 1994, at least six months before the bombing, giving you some indication of the planning that went into this process and the premeditation. They made two purchases of 1 ton each. The first one was made at the end of September, 1994, and the second one was made the middle of October; and both purchases were made in phony names. The phony name they used was Mike Havens. We'll provide you with evidence showing that Terry Nichols used that name Havens as an alias. detonation cord det cord is a nickname, an abbreviation for detonation cord, and that's what you'll use, as you'll hear the ammonium nitrate and fuel oil doesn't blow up by itself, you don't light a match and throw it on it and it explodes. You need some kind of detonation. Det cord would be used to facilitate the detonation of the explosion. buy large quantities of nitromethane and anhydrous hydrazine; and the books I've told you about describe those two chemicals as being part of the shopping list for making an ammonium nitrate fertilizer bomb. Mid-American Chemical Company Anhydrous hydrazine is usually used as a rocket fuel and it can seriously boost the explosion. Nitromethane is a racing fuel. It too can be used as one of the ingredients in ammonium nitrate fuel -- fuel oil explosive devices. Well those are the calls they made during this period of time in search of some of the various components for an explosive device, but we'll prove that they obtained -- they actually acquired large quantities of explosives, as I said just, getting the mixture, the fertilizer with the chemicals of nitromethane or anhydrous hydrazine or racing fuel doesn't itself cause an explosion unless you have something to detonate it with. got the detonation -- detonators that they needed. blasting caps were five blasting caps, Primadet 60-foot No. 8 delay. actually drew a diagram of the bomb that he intended to build. He outlined the box of the truck, and he drew circles for the barrels inside the truck, the barrels of fertilizer and fuel oil that he would place strategically in the truck to cause maximum damage, as he described it. borrowing from her Campbell soup cans out of her cupboard and placed them on the floor and showed her the shape in which he would design the bomb inside the box of the truck. And he described it as a shape charge and explained that by putting in that -- putting the barrels of explosives in a particular shape it would increase the charge in a particular direction, the direction toward the building and the plate glass windows that I've previously described. Jennifer McVeigh The Turner Diaries taught him how to mix the different ingredients, how to set up the bomb, right down to how to drill a hole between the cargo box and the cab of the truck so that he could detonate it, so that the fuse could run into the cab of the truck and he could fuse it from where he was sitting in the front of the cab. You'll hear from witness testimony that's what he said he would do. So he converted the Ryder truck from a cargo vehicle into a gigantic deadly bomb, and he drove it to Oklahoma City; and he detonated it on one of the - at one of the busiest times of the day. Bear in mind this was not 3 or 4 in the morning, when he could conceivably have detonated the bomb and possibly not have killed anyone. It was at 9:00 -- 9:02 in the morning, when everyone was in their office, business was being conducted The sound and the concussion of the blast rocked downtown Oklahoma City. It was as though it had been struck by an earthquake; and as McVeigh sped away from the scene of the crime, word quickly spread as to the location of the blast. No one in downtown Oklahoma City could have missed the sound. It ripped the air, shattered windows. It was a terrifying exploaion. and when he had tested those little specs, he determined their chemical makeup. The specs were crystals of ammonium nitrate, the very same chemical that McVeigh and Nichols had obtained in 50-pound bags in the form of the fertilizer they had purchased in central Kansas months before. She will also explain to you why a mixture of ammonium nitrate and fuel oil or racing fuel can be detonated to create an explosion; and she'll explain it's not a complicated task. She analyzed the damage to the Murrah Building and the surrounding area, and she'll explain to you why that damage is consistent with damage caused by an ammonium-nitrate-based truck bomb. She'll also explain how easy and cheap it is to make just such a bomb -- so easy, in fact, it could be built by one or two people. PETN is found in det cord, and it's a very fine powder. Det cord is sort of a narrow, hollow tubing; and when you use det cord, you often cut it. And in cutting it, cutting it open, the fine powder sifts out from inside the det cord. And it's sticky and gets all over everything. You can't really cut it without getting it on your hands and clothing. And that's the explosives residue that was found on the shirt McVeigh was wearing and on the pockets and on the earplugs that had been in his pockets. went to C.B. World in Kingman, Arizona to purchase welding or cutting supplies, but Lindsay recommended liquid oxygen for the job. The liquid oxygen was obtained from AWECO on Northern Street in Kingman, Arizona. (Reyna 10-9-95 memo) Also in the storage were four, white 55-gallon drums with no lids. These were not used in the bomb. They were the ones found by the government at Terry's house. McVeigh called a business in Junction City and, using the name "Bob Kling", inquired about renting a truck capable of carrying 5,000 pounds of cargo Ryder truck rental shop to reserve the truck 04.15.95 Terry Nichols purchased diesel fuel from Conoco station in Manhattan, KS. Detonation cord is a string of which the entire length blows up at once. The Primadet cord can be attached to a blasting cap which when it explodes, the shock jumps through the Primadet cord like a straw and explodes at the other end. The entire length does not explode like detonation cord. 04.16.95 Terry purchased 21.59 gallons of diesel fuel from a Conoco station in Junction City, Kansas He said the trailer contained a large, white canvas wrapped around a square-shaped object about 3 or 4 feet high that came to a point on top. he loaded the seven boxes of gel which weighed 50 pounds each. 04.18.95-6:30 a.m. Tim had loaded 20 fifty-pound bags of fertilizer when Terry drove up. Terry wanted to leave and wait until sunrise to finish. Tim said no. Terry drove his truck to the Pizza Hut and walked back over to the storage shed. Terry helped him load 70 fifty-pound bags of fertilizer and 3 fifty-five gallon metal drums of nitromethane. potassium nitrate Greenlight Stump Remover 04.18.95-8:15 a.m. They arrived separately at Geary Lake and began to mix the components. 7 fifty-pound bags of fertilizer and 7 twenty-pound buckets of nitromethane per 1 fifty-five-gallon drum. They weighed the buckets on a bathroom scale. When they finished, Terry nailed down the barrels and Tim changed clothes. Tim gave his dirty clothes to Terry to dispose of. Terry also took the 90 empty bags of fertilizer. The remainder of the tools were placed in the cone of the bomb. 04.18.95-8:30-12:00 pm Tim and Terry loaded the explosives in the truck at Herington Storage and went to Geary Lake where between 8:30 a.m. and noon they mixed the explosive device and put it together. 04.18.95-9:00 a.m. Witnesses at the lake told investigators that when they arrived at the lake at 9 a.m. a Ryder truck and a blue or brown pickup truck were already there. This is where federal investigators say the bomb was made from fertilizer and fuel oil. 04.19.95 McVeigh parked the truck bomb directly outside the Alfred P. Murrah Federal Building, located within the Western District of Oklahoma, during regular business and day-care hours. McVeigh caused the truck bomb to explode. 04.19.95-8:55 a.m. On NW Fourth Street Tim drove west past the Federal Building and then turned north on a one-way street. On Fifth Street he turned right. At the chain link fence in front of the Firestone he pulled over and lit the five-minute fuse. http://www.pbs.org/wgbh/pages/frontline/documents/mcveigh/mcveigh2.html http://isuisse.ifrance.com/emmaf/indterhand.html Sodium Melt any sodium compound (salt, baking soda, lye) in a PERFECTLY DRY pan. Heat it until it melts. Attach 1-6 9 volt batteries in paralell to either the pan or the melted compound. This will release deadly chlorine gas (use in well-ventilated area ONLY) for table salt, carbon dioxide (no, Im not dumb, its NOT carbon), or hydrogen and oxygen (since its O2 after it combusts with airborne oxygen). The liquid left will be relatively pure sodium. Sodium can be moistened with a spray bottle, causing combustion, or put in a bottle taped to another bottle filled with 2 parts water, 3 parts motor oil, and 10 parts any non-viscous flammable liquid like petrol, gas, hydrazine, etc. for a very good automatic combustion incendiary that goes off when thrown. www.totse.com - How to Make a Bomb From a Battery - If you take apart a regular alkaline battery, doesn't matter what size, and collect the black stuff Easy Way to Get Potassium Nitrate or on ebay Im not sure if too many people know this but you dont have to get potassium nitrate from science stores or extract it from fertalizer. All you need to do is go to your local Home Do it center, Wallmart, Home depot ect and Pick up some STUMP REMOVER. It is almost pure potassium nitrate and will work just fine with any of your explosive needs. I just tried it today and works great. It cost about 10$ CAD for 500g. It comes in small pebbles that you grind up. Good luck! Latest Developments Bush Files Papers for Re-Election Bid (AP) - President Bush launched his re-election campaign Friday with high approval ratings and a clear path to the Republican nomination - but with political clouds from the sluggish economy. Hoping to achieve a goal denied his father, Bush filed formal notice of his quest for a second term with the Federal Election Commission. The long-expected paperwork, roaming the halls of a University of Washington dorm a female resident of Terry Hall attempted abduction of a young girl in South Everett. The 13-year-old grabbed and the front pocket of her sweatshirt and ripped it. Witness: Nichols Tested Bomb Ingredients Tue May 13, 6:56 AM ET By TIM TALLEY, Associated Press Writer OKLAHOMA CITY - Timothy McVeigh (news - web sites) and bombing conspirator Terry Nichols detonated explosives in the Arizona desert and experimented with ingredients that were later used in the Oklahoma City bombing, McVeigh's close friend testified. Michael Fortier, testifying at a preliminary hearing for Terry Nichols, also said McVeigh had worked out plans for the Oklahoma City bombing six months before a bomb ripped through the federal building, killing 168 people. Fortier said McVeigh told him in October 1994 that he and Nichols planned to blow up the Alfred P. Murrah Federal Building (news - web sites). He discussed how he would take ammonium nitrate and fuel and mix it up and put it in 55-gallon drums, Fortier testified Monday. Nichols was at home in Kansas the day the bomb exploded. But prosecutors said he helped McVeigh deliver a getaway car to Oklahoma City and worked with McVeigh to pack the 4,000-pound bomb inside the truck the day before the bombing. Required and Suggested Readings are Found in: Brown, T.L.; LeMay, H.E. Jr.; Bursten, B.E.Chemistry: The Central Science, 8th ed. Hill, J. W. and D. K. Kolb. Chemistry for Changing Times, 7th ed. Prentice-Hall, c.1995. Snyder, C.H. The Extraordinary Chemistry of Ordinary Things; 2nd Edition Brady, James, E. and J. R. Holum. Chemistry: The Study of Matter and its Changes.John Wiley, c. 1996. Birk, J. P. Chemistry. Houghton,-Miflin, c. 1994. Chang, R. Chemistry, 5th ed. McGraw-Hill, c. 1994. Atkins, P. W. and L. Jones, Chemistry: Molecules, Matter, and Change, 3rd ed. W.H. Freeman, c. 1997. The Closest star to the Earth The Nearest Stars, as Seen from the Earth Adapted from Norton's 2000.0, 18th edition (copyright 1989, Longman Group UK) with additional comments taken from Bill Baity's Sky Pages These are our closest neighbors! Note that this list is continually changing as astronomers discover nearby stars with ever more sensitive detectors in a variety of spectral ranges, especially the infrared, where numerous small stars emit their energy. Recall that the brightest magnitudes are the largest negative numbers. Common Name Scientific Name Distance (light years) Apparent Magnitude Absolute Magnitude Spectral Type Sun - -26.72 4.8 G2V Proxima Centauri V645 Cen 4.2 11.05 (var.) 15.5 M5.5Vc Rigil Kentaurus Alpha Cen A 4.3 -0.01 4.4 G2V Alpha Cen B 4.3 1.33 5.7 K1V Barnard's Star 6.0 9.54 13.2 M3.8V Wolf 359 CN Leo 7.7 13.53 (var.) 16.7 M5.8Vc BD +36 2147 8.2 7.50 10.5 M2.1Vc Luyten 726-8A UV Cet A 8.4 12.52 (var.) 15.5 M5.6Vc Luyten 726-8B UV Cet B 8.4 13.02 (var.) 16.0 M5.6Vc Sirius A Alpha CMa A 8.6 -1.46 1.4 A1Vm Sirius B Alpha CMa B 8.6 8.3 11.2 DA Ross 154 9.4 10.45 13.1 M3.6Vc Ross 248 10.4 12.29 14.8 M4.9Vc Epsilon Eri 10.8 3.73 6.1 K2Vc If directions to these stars were included, you could make a map a nd see that they are distributed around us more or less randomly. What can we learn from this information? Quite a lot. We live very close (500 lightseconds) to a star. This is probably a necessary condition for the originination and maintenance of life. Stars are very far apart (average about 8 lightyears for the closest dozen), compared to their size (about 2 lightseconds for the Sun); by a factor of 250 million or so. Many stars occur in multiple systems, shown here by the suffixes A, B and C from brightest to dimmest. In fact, about 55% of stars in this list are in multiple systems. The nearest star is a triple. And we may be missing many dim stars. Most of the nearby stars are dimmer (higher numbers for absolute magnitude) than our Sun, by factors of 100 to 10,000. Earth Solar Distance mean: 149.6 M km Solar Distance max.: 152.0 M km Solar Distance min.: 147.0 M km Orbital Period: 1.000 Earth year Orbital Velocity: 29.79 km/s Orbital Inclination: 0.00° Orbital Eccentricity: 0.017 Rotation Period: 1.000 Earth day Rotation Inclination: 23.44° Diameter: 12756 km Volume: 1.000 Earth volume Mass: 1.000 Earth mass Density: 5.5 Surface Gravity: 1.00 G Escape Velocity: 11.2 km/s Albedo: 0.36 Primary Atmospheric Gas: Nitrogen Temperature Range: -90/+60°C Natural Satellites: 1 Comments: Day=23h56m04s, year=365.2425d, mass=5.976x10^24 kg, surface gravity=9.8 m/s. Mars Solar Distance mean: 227.9 M km Solar Distance max.: 249.1 M km Solar Distance min.: 206.7 M km Orbital Period: 1.881 Earth year Orbital Velocity: 24.1 km/s Orbital Inclination: 1.85° Orbital Eccentricity: 0.093 Rotation Period: 1.029 Earth day Rotation Inclination: 23.98° Diameter: 6787 km Volume: 0.150 Earth volume Mass: 0.107 Earth mass Density: 3.9 Surface Gravity: 0.38 G Escape Velocity: 5.03 km/s Albedo: 0.16 Primary Atmospheric Gas: Carbon Dioxide Temperature Range: -50/+25°C Natural Satellites: 2 Comments: 25 km-high Olympus Mons is the tallest mountain, and 4000 km-long Mariner Valley is the largest canyon in the Solar System. Jupiter Solar Distance mean: 778.3 M km Solar Distance max.: 815.7 M km Solar Distance min.: 740.9 M km Orbital Period: 11.86 Earth year Orbital Velocity: 13.07 km/s Orbital Inclination: 1.30° Orbital Eccentricity: 0.048 Rotation Period: 0.415 Earth day Rotation Inclination: 3.067° Diameter: 142000 km Volume: 1319 Earth volume Mass: 317.9 Earth mass Density: 1.3 Surface Gravity: 2.64 G Escape Velocity: 60.2 km/s Albedo: 0.43 Primary Atmospheric Gas: Hydrogen Temperature Range: -150°C Natural Satellites: 16 Comments: Jupiter is the largest planet in the Solar System. Its Great Red Spot is a storm about three times the diameter of Earth. Mercury Solar Distance mean: 57.9 M km Solar Distance max.: 69.7 M km Solar Distance min.: 45.9 M km Orbital Period: 0.241 Earth year Orbital Velocity: 47.87 km/s Orbital Inclination: 7.00° Orbital Eccentricity: 0.206 Rotation Period: 58.65 Earth day Rotation Inclination: 0.0° Diameter: 4880 km Volume: 0.056 Earth volume Mass: 0.055 Earth mass Density: 5.5 Surface Gravity: 0.38 G Escape Velocity: 4.3 km/s Albedo: 0.06 Primary Atmospheric Gas: Sodium Temperature Range: -170/+350°C Natural Satellites: 0 Comments: At a pressure of 10^-12 bars, Mercury's atmosphere is almost non-existent. Neptune Solar Distance mean: 4497 M km Solar Distance max.: 4556 M km Solar Distance min.: 4437 M km Orbital Period: 164.8 Earth year Orbital Velocity: 5.42 km/s Orbital Inclination: 1.76° Orbital Eccentricity: 0.009 Rotation Period: 0.673 Earth day Rotation Inclination: 28.8° Diameter: 49500 km Volume: 57 Earth volume Mass: 17.2 Earth mass Density: 1.6 Surface Gravity: 1.14 G Escape Velocity: 24 km/s Albedo: 0.35 Primary Atmospheric Gas: Hydrogen Temperature Range: -220°C Natural Satellites: 8 Comments: Neptune was discovered in 1846. It has a giant dark spot which is a storm about the same diameter as Earth. Pluto Solar Distance mean: 5900 M km Solar Distance max.: 7375 M km Solar Distance min.: 4425 M km Orbital Period: 247.7 Earth year Orbital Velocity: 4.7 km/s Orbital Inclination: 17.2° Orbital Eccentricity: 0.248 Rotation Period: 6.388 Earth day Rotation Inclination: 98.8° Diameter: 2400 km Volume: 0.007 Earth volume Mass: 0.002 Earth mass Density: 2.0 Surface Gravity: 0.07 G Escape Velocity: 1.05 km/s Albedo: 0.4 Primary Atmospheric Gas: Methane Temperature Range: -240°C Natural Satellites: 1 Comments: Pluto was discovered in 1929. During part of its year, Pluto's highly eccentric orbit takes it inside that of Neptune's. Saturn Solar Distance mean: 1427 M km Solar Distance max.: 1507 M km Solar Distance min.: 1347 M km Orbital Period: 29.46 Earth year Orbital Velocity: 9.6 km/s Orbital Inclination: 2.49° Orbital Eccentricity: 0.056 Rotation Period: 0.445 Earth day Rotation Inclination: 26.73° Diameter: 120000 km Volume: 744 Earth volume Mass: 95.17 Earth mass Density: 0.7 Surface Gravity: 1.16 G Escape Velocity: 32.3 km/s Albedo: 0.61 Primary Atmospheric Gas: Hydrogen Temperature Range: -180°C Natural Satellites: 19 Comments: Saturn is most famous for its spectacular ring system. Uranus 51100 x 14.5 255500 204400 51100 =53399500 Solar Distance mean: 2870 M km Solar Distance max.: 3004 M km Solar Distance min.: 2735 M km Orbital Period: 84.01 Earth year Orbital Velocity: 6.8 km/s Orbital Inclination: 0.77° Orbital Eccentricity: 0.047 Rotation Period: 0.720 Earth day Rotation Inclination: 97.92° Diameter: 51100 km Volume: 64 Earth volume Mass: 14.5 Earth mass Density: 1.3 Surface Gravity: 0.91 G Escape Velocity: 21 km/s Albedo: 0.35 Primary Atmospheric Gas: Hydrogen Temperature Range: -210°C Natural Satellites: 15 Comments: Uranus was discovered in 1781. Its rotational axis is nearly parallel to the plane of its orbit. Venus Solar Distance mean: 108.2 M km Solar Distance max.: 109.0 M km Solar Distance min.: 107.4 M km Orbital Period: 0.615 Earth year Orbital Velocity: 35.02 km/s Orbital Inclination: 3.39° Orbital Eccentricity: 0.007 Rotation Period: 243 Earth day Rotation Inclination: 178° Diameter: 12100 km Volume: 0.853 Earth volume Mass: 0.815 Earth mass Density: 5.2 Surface Gravity: 0.91 G Escape Velocity: 10.4 km/s Albedo: 0.76 Primary Atmospheric Gas: Carbon Dioxide Temperature Range: -33/+480°C Natural Satellites: 0 Comments: Venus, the hottest planet in the Solar System, has a year which is slightly shorter than its day. Mercury Mercury.txt Venus Venus.txt Earth Earth.txt Mars Mars.txt Jupiter Jupiter.txt Saturn Saturn.txt Uranus Uranus.txt Neptune Neptune.txt Pluto Pluto.txt Charon is a Pluto Moon Chemistry 102 G -- Fundamentals of Chemistry II -- Spring, 2000 Syllabus and Schedule Textbook: "The Extraordinary Chemistry of Ordinary Things" 3rd Edition" Snyder; John Wiley & Sons; 1998 Revised 21 January 2000 Examinations are given on underlined dates. There is no class on dates in parentheses. Date Topics, Activities and Chapters Jan 19,21 Introduction, Ch 12 (Surfactants) 24,26,28 12,10 (Oxidation and Reduction); EXTRA CREDIT QUIZ 31, Feb 2,4 10 7,9,11 13 (Chemicals, Pollution, and the Environment) 14,16,18 13 21,23,25 14 (Energy, Food, Fats, and Oils) 28, Mar 1,3 14,15 (Carbohydrates) 6,8,10 16 (Proteins and the Chemistry of Life) (13,15,17) SPRING RECESS; NO CLASS 20,22,24 16, 17 (The Chemicals of Food) PLEASE NOTE: COURSES MAY NOT BE DROPPED AFTER MONDAY, MARCH 27. 27,29,31 17; 18 (Poisons, Toxins, Hazards, and Risks) Apr 3,5,7 18, 19 (Polymers and Plastics) 10,12,14 19, 20 (Cosmetics and Personal Care) 17,19,21 20, 21 (Medicine and Drugs) 24,26,28 21; Review for Final Examination; makeup May 8 FINAL EXAMINATION, 2:00 - 4:30 ISBN: 0030052033 Voyages Through Universe by Fraknoi List Price:$40.95 Price:$40.95 $3.00 postage. Poisons All preparation and handling of toxic substances must be conducted with great care. Work in a well-ventilated area, wear gloves, goggles and a respirator. The operative and those assisting can become poisoned by, fumes, dust, contacting toxins and dusts with bare skin or mucous membranes. Be Very Cautious! I haven't provided much information on identifying the plants or mushrooms required for making some of these poisons because detailed information on this subject is widely available in books and on the internet. There are dozens of other toxins which the operative could produce or obtain but I have chosen to include only the most basic ones which are readily available (Cobra or pufferfish toxin may be very deadly but how are you going to obtain some without going to lengths which make it impractical?). Ethylene Glycol This is the active ingredient in automotive anti-freeze. Be sure to use the automotive rather than the plumbing variety, which is non-toxic. Ethylene Glycol is deadly poisonous and there isn't much that a doctor can do for a victim who has ingested more than a cup or so of it. Ethylene Glycol has (apparently) a sweet, pleasing taste and is easily masked with alcohol or strong tasting soft drinks, such as colas. A syringe full of this toxin will also kill, but not quickly enough to be considered for selective assassination. The best application for this poison is to top up a half-empty liquor bottle with it and leave it where some unlucky non-White will find it. Ethylene Glycol is a bright yellow-green color and should be mixed with a dark beverage. The victim will be more likely to drink the poison if the original seal on the cap is unbroken, so purchase some new caps from a beer + winemaking supply store. Put the bottle in a paper bag from the liquor store, adding a receipt is a nice touch as well. Leave the bottle in a non-White neighborhood or where some particular target is likely to find it. Methyl Alcohol Also known as Wood Alcohol, this substance is deadly if more than just a few mouthfuls are swallowed and medical treatment is not received soon after ingestion. It is indistinguishable from alcohol in appearance, smell and taste. Methyl Alcohol can be purchased at hardware and paint stores where it is sold as paint remover. It and can be applied in a similar manner as Ethylene Glycol except that there is no need to mix it with any real booze. Cyanide Cyanide occurs naturally in the seeds of a number of common plants. Peach pits contain a very high concentration of cyanide. The pits must be crushed and powdered and the cyanide extracted from this powder. The process of extracting pure cyanide from these sources is nearly impossible without some specialized equipment, though a fairly powerful toxin can be produced from a distilled solution of the powdered peach pits. Quite a large dose of unconcentrated cyanide must be ingested in order to be fatal. The operative should try to obtain this toxin by other means. Cyanide has a number of legitimate uses which make it possible to obtain on the civilian market. The real advantage of cyanide is that it acts very quickly, killing the target within minutes rather than hours. Lethal dosage is at least 500 milligrams (mg). Deadly hydrocyanic gas is produced when cyanide is mixed with a strong acid. This gas is invisible and has a slight smell of almonds. Cyanide gas could be used effectively in crowded areas with poor ventilation such as nightclubs, subways or shopping malls. Arsenic Arsenic has been known since ancient times. The pure element can be obtained by heating a common ore called arsenopyrite (FeAsS). Other common minerals are realgar (As2S2); orpiment (As 2S3); and arsenic trioxide (As2O3); occasionally the pure element is found in nature. Arsenic also occurs in place of some of the sulfur in the sulfides that are the principal ores of many of the heavy metals. When these ores are roasted at 613 Degrees C (1135 Degrees F), the arsenic sublimes (turns from solid directly into gaseous form) and can be collected from the dust as a by-product. This is dangerous work as the fumes can poison anyone not in a protective suit and a special chemical respirator. The operative would have an easier time trying to purchase this toxin. It is a very common element and has a number of legitimate uses. Conium Alkaloids (Poison Hemlock + Water Hemlock) Poison Hemlock is native to Europe. However, it is now widely distributed across the United States and Canada, especially in the Northern states. It is common along roadsides, hiking trails, ditches and field borders. Poison Hemlock can grow to be about 6 to 10 ft. tall. It has leaves and white flowerheads resembling those of parsnips, carrots, and Water Hemlock. It has a fleshy, white taproot, a main stem with characteristic light red spots and a disagreeable smell. All plant parts are poisonous. However, the seeds contain the highest concentration of poison. The conium alkaloids are volatile and can even cause toxic reactions when inhaled. Water Hemlock does not have the same main taproot and stem. Instead, Water Hemlock has a branching, tuberous root stalk. The lower part of the stem of the Water Hemlock is divided into chambers which contain its toxicant. The seeds of the Poison Hemlock or the lower stem of the Water Hemlock should be processed in a similar fashion as the castor bean (ricin). Ingestion is the most reliable method of application and hemlock lends itself to being concealed in food or drink. A solution made from the powdered toxin can be injected but, again, death is not quick and the target may be able to spoil the operative's plans for escape. Belladonna Belladonna is also known as deadly nightshade and contains a highly toxic substance known as Atropine. All parts of this plant are toxic but the highest concentrations are found in the berries. Ingestion of just a few of the raw berries can kill an adult. The berries can be processed into a purer toxin in a similar fashion as castor beans (Ricin). Ingestion is the best delivery method, but injection will also work. Castor Bean (Ricin) The fleshy pulp left over from the de-hulled castor bean is very highly toxic. The active toxin is Ricin, an extremely deadly poison, which, in its pure form, requires about 1 milligram (mg) to kill an adult. Procedure: 1.Obtain some castor beans from a garden supply store. 2.Put about 2 ounces of hot water into a glass jar and add a teaspoon full of lye. Mix it thoroughly. 3.Wait for the lye/water mixture to cool 4.Place 2 ounces of the beans into the liquid and let them soak for one hour. 5.Pour out the liquid being careful not to get any on exposed skin. 6.Rinse the beans off with cool water and then remove the outer husks with tweezers. 7.Put the bean pulp into a blender or coffee grinder with 4 ounces of acetone for every 1 oz. of beans. 8.Blend the pulp/acetone until it looks like milk. 9.Place the milky substance in a glass jar with an airtight lid for three days. 10.At the end of three days shake the jar to remix everything that’s started to settle then pour it into a coffee filter. Discard the liquid. 11.When no more liquid is dripping through the filter, squeeze the last of the acetone out of it without losing any of the bean pulp. 12.Spread the filter out on a pan covered with newspaper and let it dry stand until it is dry. 13.The final product must be as free of acetone and other contaminants as possible. If it is not powdery but still sort of moist and pulpy it must be combined with the appropriate amount of acetone again and let sit for one day. Then repeat steps 9-12 again until a nice dry powder is produced. Ricin's big allure, besides its potency, is that it is virtually untraceable and produces food poisoning-like symptoms. This toxin takes from 12 to 24 hours to bring about death, given a sufficient dosage. If the target survives longer than this the chances of recovery are quite good. There is no effective antidote to this toxin.. Ricin can be applied by ingestion or injection, it is so toxic that even inhalation of the dust can be fatal. This poison lends itself to all sorts of application methods. For example; in 1978, Ricin was used to assassinate Georgi Markov, a Bulgarian journalist who spoke out against the Bulgarian government. He was stabbed with the point of an umbrella while waiting at a bus stop near Waterloo Station in London. A tiny metallic pellet was found embedded in his leg that had presumably contained the Ricin toxin. Abrin (Rosary Pea) Abrin is a highly toxic substance found in the seeds of the rosary pea. Abrin toxin inhibits protein synthesis, causing symptoms such as internal bleeding, intestinal upset, and the irritation of mucous membranes. The rosary pea is extremely toxic and it would only take one fully chewed seed to cause death in humans. The seeds should be processed in a similar fashion as the castor bean (Ricin). The high lethality of this toxin allows it to be applied reliably by injection or ingestion. Very little toxin is required to produce fatality in even a healthy adult. Deadly Galernia Also known as the Autumn Skullcap, this is another very deadly mushroom with poisoning effects identical to the Aminita. Dried and powdered caps cap be applied by ingestion. Aconitum Napellus This plant has had various names since antiquity including wolfsbane (because its root and raw meat were used as bait to kill wolves), monks-hood (because the hooded flower resembled a monk's cowl), leopard killer, brute killer, and woman killer. The root contains the highest concentration of toxin. Once dried and powdered this toxin can be applied by injection or ingestion. This toxin was used in ancient times as an arrow poison throughout Europe and the Near East. In Roman times it was also used as an ingested poison. The active constituent, aconitine, has been shown to reduce the ion selectivity of sodium channels with a resultant increased uptake of sodium and other ions via these channels. This results ultimately in production of cardiac arrhythmia, depression of respiration and death within a few hours. Oleander Oleander, also known as Rose Laurel, is an evergreen shrub of the Dogbane family, native to the Mediterranean region of Europe. It has leathery leaves, which are opposite or in threes. The sap, used in rat poison, is very toxic; a single leaf may contain a lethal dose. The leaf tips contain the highest concentration of toxin. Dried leaves can be crushed into powder and applied by ingestion, dosage should be the powder of 3-4 leaves. Chlorine Gas A deadly gas can be produced by mixing pool chlorinating chemicals, such as HTH, with sulfuric acid. Prills, pucks, powdered or any other form of the HTH should be dropped into a container of the acid just before the attack. The larger the area to be filled with gas, the more HTH and acid will be required. The gas produced is visible, burns the eyes and throat and has a very strong chlorine smell. Use of this type of toxin will be most effective if deployed in crowded and poorly ventilated locations such as nightclubs, shopping malls, or subways. The lab technician found that both samples tested positive for urea nitrate, the explosive component of the infamous fertilizer bomb. 9 pin db9 connector wire attach to 2 3 5 august 15 How to make a Bomb Alright, so you want to make an inexpensive pressure bomb without messing with Drano and sulphuric acid and all those other dangerous chemicals. which can burn the crap out of your skin if your not careful.) All you need is a battery, a 2 litre plastic bottle, and hydrogen peroxide(3% by solution is fine), a hammer and a sharp nail. The size of the battery doesn't matter, although I don't recommend some of the D batteries because the new ones aren't dry cell anymore, and the concentrated sulphuric acid inside can burn you. First, you might want to move everything outside, cause if you don't know what you're doing this can make a mess. Take the battery that you're using, I prefer a duracel or energizer AA battery, and set it up vertical, so the negative side is facing towards you. That's the flat side to those who don't have a clue of what I'm talking about) Now, while holding the battery with one hand, take the nail and place it on the centre of the negative side of the battery with the point of the nail against the battery. With the hand that it holding battery, you should also hold the nail in place. Gently, and I mean gently, tap the nail with the hammer until a tiny hole is in the battery. BE CAREFUL WHILE DOING THIS!! Batteries are under pressure from the chemical reaction that takes place in them, so move your head to the side, you don't want to get sprayed! A little air should spray out of the battery, this is good, you just relieved the pressure and now the battery is basically harmless. Now, however you can get the battery open is your choice, I prefer using a hacksaw and sawing it lengthwise, but whatever you want to do. Once it's open, you will see a whole lot of black stuff and a rolled up piece of paper in the middle with silver chunks of metal. The black stuff is Magnesium Oxide, this is what you want to collect. The silver stuff is Zinc) Use the nail to scrape it from the battery, never your hands. It contains a small amount of Sulphuric Acid in it, not enough to harm you, but some people react to things different than other people. If you have gloves, use them!!! Once you have all the "Black Stuff" from the battery, let it sit for about an hour in the sun or under a light, this will dry it out. Once dry, crush it into very fine granules so there are no chunks. You don't have to let it dry, but the bomb will be better if you crush it up. Alright! You're almost done, all you have to do now is pour 2 16oz. bottles of Hydrogen Peroxide in the 2 litre bottle and add the "Black Stuff!" Voila!! there's your bomb! When you add the Magnesium Oxide, screw the cap on as fast as you can, make sure it's tight, real tight, throw it and run! You should have a very nice explosion in about 10-20 seconds! This method is tried and true, works every time, if you do it like I said. Be careful though, I am not taking any responsibility for your behaviour! You do what you want with this information! First you need: a battery dry cell (dead or alive) 2 liter bottle 32 oz. of Hydrogen peroxide (3% solution is fine) hammer sharp nail saw First you take the nail and hammer and pop a hole in the negative end of the battery. Be careful when you do this because there is some acid in the battery. Then use the saw to cut the battery in half. Then use the nail to scrape out the Magnesium Oxide. ( it is the black stuff) Then lay it out under the sun or a lamp untell it is dry. Once it is dry then cru#*@! up. Now take the hydrogen peroxide and pore it in to the 2 liter bottle. Then put the magnesium oxide in the bottle and put the cap on as good and as fast as you can. Put ti on the ground and run away. In about 15-20 seconds you will hear a loud BANG!!!! Comments its not hydrogen, its oxygen.. mix draino or any other acid/base w/ any metal (foil works best) and u got hydrogen. Mix it 50/50 w/ oxygen and u’ve got one badass explosive Hindenberg Bomb Needed: Balloon 1 Bottle 1 Liquid Plumber 1 Piece Aluminum foil 1 Length Fuse Fill the bottle 3/4 full with Liquid Plumber and ad a little piece of aluminum foil to it. Put the balloon over the neck of the bottle until the balloon is full of the resulting gas. This is highly flammable hydrogen. Now tie the balloon. Now light the fuse, and let it rise. When the fuse contacts the balloon, watch out!!! ok you need the toleit bowl cleaner the works a 20oz bottle aluminum foil and the top to the empty 20oz bottle what u do is empty the 20oz bottle and pour the works into the 20oz bottle until it is about 1/4 fill the make about 5 aluminum foil balls that could fit through the top of the 20oz bottle next put the aluminum foil n and close the top twist it tightly then set it down and walk away make sure u get about at least 7 ft from the bottle and have fun this work well on somone door step at 1 in the morning but this time get a liter ad make it lite now take a ruber band and wrap it on the gass so it stays lit now wrap it to the bottle still lit and flaming lay the bottle on its side and wrap the liter still lite to the side where ther is air the top half now when u put the aluminum foil balls in and close the top it will start to reacet and when it goes off all of the hydrogen will rise up to the liter causeing the liter to exsplode be carful. Your Personal Day of Death is... Monday, October 22, 2040 Homicide Investigation - Chandra Ann Levy Characteristic Description Race and Gender White Female Height 5' 4" Weight 108 lbs Hair Dark brown Eyes Hazel Latest News: Chandra Levy Homicide Investigation, Response to Media Inquiries 9-29-02 News Release Search of Chandra Levy Crime Scene Concluded 6-25-02 News Release Continuing Search of Rock Creek Park: Additional Bones Discovered 6-11-02 News Release Update on Discovery of Leg Bone 6-7-02 News Release Additional Leg Bone Discovered 6-6-02 News Release The MPDC seeks the public's assistance in locating a gold ring worn by Ms. Levy The Metropolitan Police Department is seeking information about the homicide of 24-year-old Chandra Ann Levy. Ms. Levy was reported missing in May 2001. On May 22, 2002, her skeletal remains were found in a heavily wooded area of Rock Creek Park in Northwest Washington, DC. On May 28, 2002 the DC Medical Examiner's Office ruled Ms. Levy's death was a homicide; the precise cause of death remains undetermined. Chandra Levy's size .04 14-karat gold pinky ring, which bears the engraved cursive initials CL with two diamond chips, one on either side of the initials. Post Apple Scientific, Inc. Reagents Reagent Name Grade Shipping Comments Size Quantity Price Magnesium Oxide, Powder Reagent 100g Single Unit $15.00 Magnesium Oxide, Powder Reagent 100g 12 Pack $131.76 Acetone ACS Limited quantity 100mL Single Unit $7.49 Acetone ACS Limited quantity 100mL 12 Pack $60.12 Acetone ACS Limited quantity 500mL Single Unit $14.00 Acetone ACS Limited quantity 500mL 12 Pack $119.88 Poison packs require $13.50 in addition to other freight charges Sodium Hydroxide, Pellets ACS 25g Single Unit $5.00 Sodium Hydroxide, Pellets ACS 25g 12 Pack $44.88 Sodium Hydroxide, Pellets ACS 100g Single Unit $9.36 Sodium Hydroxide, Pellets ACS 100g 12 Pack $84.48 Sodium Hydroxide, Pellets ACS 500g Single Unit $16.75 Sodium Hydroxide, Pellets ACS 500g 12 Pack $146.76 POST APPLE SCIENTIFIC, INC. 8893 Gulf Road North East, PA 16428-4298 Ortho-Toluidine, 500mL - Single Unit PAS-C-5852 $36.00 Sub Total $36.00 Tax $0.00 Zip/Postal Code Shipping $39.64 Total $75.64 Sodium Hydroxide, Pellets, ACS, 25g - 12 Pack PAS-C-7470-0025-12-N $40.39 Sub Total $40.39 Tax $0.00Zip/Postal Code Shipping $5.44 Total $45.83 331 Sage Lane, Santa Monica 90402-1119 137 W. 25th St., New York, NY 10001 A&R Department Main Street Seed And Supply, Co. Bay Farm Services, Inc. 401 Main Street Bay City, Michigan 48706 $ 1.50 minimum shipping charge on small orders. FLCB1 Castor Bean 1 Pound $40.00 lb 1 $6.00 Grand Total: $46.00 1280 Seeds http://www.mainstreetseedandsupply.com/flowerseed.htm Home Harvest Garden Supply, Inc. 3807 Bank Street Baltimore, MD 21224 $1.50 postage Caster Bean Seeds Order #0011462 FM Castor Bean Choice Mixture $1.79 Half Price .89 CASTOR BEAN. Burning of the mouth and throat, excessive thirst and convulsions. One or two seeds are near the lethal dose for adults. $1.50 #A1032 Castor Bean 10 seeds Annual If you would like to pay by check, please fill out our generic form and mail it today Sharon Howell 2270 S. New Lothrop Lennon MI 48449 contains information on making ricin glass jars, test tubes and castor beans Castor beans are grown all over the world and the toxin is relatively easy to produce. It can be used to poison water or food, can be sprayed into the air or injected into a person. Ricin can kill within three days of exposure. said two-thirds of a gram of the poison could have killed 125 people if inhaled. Anthrax Medical Details by Kenneth Todar University of Wisconsin-Madison The anthrax bacillus was the first bacterium shown to be the cause of a disease. In 1877, Robert Koch grew it in pure culture, demonstrated its ability to form endospores, and produced experimental anthrax by injecting it into animals. Bacillus anthracis is a very large, Gram positive, sporeforming rod (1-1.5um x 4-10um). The organism is readily cultivated on ordinary nutrient medium and grows best aerobically, but will also multiply under anaerobic conditions. Genotypically and phenotypically, it is very similar to Bacillus cereus, which is isolated readily from soil habitats. However, the natural history of B. anthracis remains obscure. Pathogenicity Anthrax is primarily a disease of domesticated and wild animals, particularly herbivorous animals. Humans become infected incidentally when brought into contact with diseased animals, their hides or hair, or their excrement. Many species of animals and birds can acquire the disease naturally. My experiment castor bean seeds in closed container for several days, and a green colored powder forms on the seeds. Some of the green colored powder was loose. Exploring the X-Ray Universe by Frederick D. Seward (Author), Philip A. Charles (Author) List Price: $55.00 Price:$55.00 amazonbooks Hardcover: 398 pages ; Dimensions (in inches): 0.95 x 9.91 x 7.06 Publisher: Cambridge Univ Pr (Pap Txt); (December 1995) ISBN: 0521437121 Astronomy Textbooks for Astronomy Courses ASTR313 SLN Course Title Author UBS Price Notes New 8422 ASTR 313 BEFORE BIG SCIENCE NYE $18.95 MODERN THEORIES OF THE UNIVERSE CROWE $17.95 8405 ASTR 301 INTROD ASTRONOMY & ASTROPHYSICS (4E 98) ZEILIK $113.25 1464 ASTR 101 STARS GALAXIES & COSMOLOGY (2E 02) BENNETT $48.75 1490 ASTR 423 EXPLORING THE X-RAY UNIVERSE CHARLES $55.00 Electrical Engineering 2689 EE 215 ELECTRIC CIRCUITS (PACK) NILSSON $103.25 Electric Circuits, Revised Printing by James William Nilsson, James W. Nilsson, Susan A. Riedel List Price:$113.00 Price: $113.00 amazonbooks.com Hardcover: 1030 pages ; Dimensions (in inches): 1.75 x 9.50 x 8.25 Publisher: Prentice Hall; 6th edition (August 16, 2000) ISBN: 0130321206 Introductory Astronomy and Astrophysics by Michael Zeilik, Stephen A. Gregory, Elske V. Smith Availability: Usually ships within 1-2 business days 3 used & new from $10.00 Edition: Hardcover Hardcover: ; Dimensions (in inches): 1.25 x 10.50 x 8.50 Publisher: International Thomson Publishing; 3rd edition (January 1998) ISBN: 0030316979 Other Editions: Paperback (2nd) | Spiral-bound (4th) PH224 Astronomy Syllabus PH224 Astronomy MWF 2:10 p.m. Spring 2003 Instructor I, Dr. Dale Pleticha, am your instructor (pleticha@faith.gordon.edu, MacDonald 204, ext. 4373). I will announce my office hours the first week of class. To guarantee seeing me during my office hours, schedule an appointment by phoning me or by signing your name on my office door appointment calendar. I will post class information on our class web site; its home page is at www.gordon.edu/physics/ph224/. Prerequisites 1. PH224 requires you to know college algebra, but not trigonometry or calculus. If your algebra abilities are poor, you might not want to take this course until you improve your math skills. 2. There is a time scheduling prerequisite for PH224. At the start of this course, intentionally block-out six to eight hours of time per week for astronomy in your semester schedule. Not counting in-class time, that is the average amount of time a student will need to spend on astronomy in order to succeed in this course. Objectives 1. Our first objective is to learn more about the physical aspects of our universe. The earth is but an infinitesimal speck in the vastness of God's magnificent creation. All those regions outside of the earth are the domain of astronomy. 2. Our second objective is to sharpen our skills of observation, analysis, synthesis, and prediction (i.e., our scientific skills). In doing so we will better understand the power and limitations of scientific methodology, and hopefully we will become better citizens and stewards of the universe. We will focus not simply on astronomical facts but on how we know those facts to be true. 3. Our third objective is to enjoy the grandeur, complexity, orderliness, and beauty of creation--and of its Creator. Hopefully we will more deeply appreciate our place in creation. 4. Our fourth objective is to think about some of the issues at the interface between astronomy and theology. Textbook Our textbook is Horizons: Exploring the Universe, Seventh Edition, by Micahel A. Seeds. The book is published by Brooks/Cole: Thompson Learning. Requirements 1. Attendance: You should attend every class promptly at 2:10 p.m. If you ever do arrive late for class, please be seated quietly; do not disturb your on-time classmates. You are responsible for everything discussed or assigned in class. Evaluation For each activity the instructor will announce the minimum number of points needed for an A-, B-, C-, and D-. The grade cut-offs for final course grades will be the sum of the cut-offs for the individual activities. activities---points ------------------------------------------- Project 1 = 125 points Project 2 = 125 points Exam 1 = 250 points Exam 2 = 250 points Exam 3 ("Final Exam") = 250 points ------------------------------------------- total = 1000 points For each entire class session you attend and during which you submit a short written response to a question I pose, I will award you one extra credit point. There will be no other extra credit available in this course, and there will be no re-tests. UofW ASTR 101 Astronomy (5) NW, QSR Introduction to the universe, with emphasis on conceptual, as contrasted with mathematical, comprehension. Modern theories, observations; ideas concerning nature, evolution of galaxies; quasars, stars, black holes, planets, solar system. Not open for credit to students who have taken 102 or 201; not open to upper-division students majoring in physical sciences or engineering. Instructor Course Description: Ana M. Larson Paula Szkody ASTR 102 Introduction to Astronomy (5) NW, QSR Emphasis on mathematical and physical comprehension of nature, the sun, stars, galaxies, and cosmology. Designed for students who have had algebra and trigonometry and high school or introductory level college physics.. Cannot be taken for credit in combination with ASTRO 101 or ASTRO 301. Prerequisite: either PHYS 101, PHYS 110, or PHYS 114. Instructor Course Description: Ana M. Larson ASTR 150 The Planets (5) NW, QSR For liberal arts and beginning science students. Survey of the planets of the solar system, with emphases on recent space exploration of the planets and on the comparative evolution of the Earth and the other planets. Instructor Course Description: Ana M. Larson ASTR 190 Modern Topics in Astronomy for Non-Science Majors (3/5, max. 10) NW Topics of current interest, such as origin of chemical elements, novae and supernovae, white dwarfs, neutron stars, black holes, active galaxies, quasars, or interstellar medium and astrochemistry. Choice of topics depends on instructor and class interest. Prerequisite: either one 100- or one 200-level ASTR course. ASTR 201 The Universe and the Origin of Life (5) NW, QSR Sequel to 101 or 102, emphasizing modern views of the atomic and molecular evolution of the universe from the initial "big bang" through the formation of the solar system and the emergence of biological forms on the earth. The latter part of the course considers questions about the existence of, and communication with, extraterrestrial intelligent life, and finally the ultimate fate of the cosmos. ASTR 210 Distance and Time: Size and Age in the Universe (5) NW, QSR Space and time as basic concepts in physical science. How we define and measure them, how the concepts have developed over the centuries, and how modern measurements allow us to determine the size and age of the universe. ASTR 211 The Universe and Change (5) NW, QSR Gravity as central to the form and evolution of the universe. Conceptual formulation of gravity from the Renaissance to Einstein. Its consequences from the falling of an apple to the slowing of the expansion of the universe. Instructor Course Description: Paul Boynton ASTR 212 Life in the Universe (5) NW, QSR Nature and origin of cosmic large numbers. Steps to the formation of life, formation of planets (stars, galaxies, a long-lived universe), the anthropic principle. Searches for other planetary systems and extraterrestrial life. ASTR 301 Astronomy for Scientists and Engineers (3) NW Introduction to astronomy for students in the physical sciences or engineering. Topics similar to 101, but the approach uses more mathematics and physics. Prerequisite: PHYS 123. ASTR 313 Science in Civilization: Physics and Astrophysics Since 1850 (5) I&S/NW Organization and pursuit of the physical and astrophysical sciences, focusing on the major unifying principles of physics and astronomy and the social and cultural settings in which they were created. Offered: jointly with HIST 313. ASTR 321 The Solar System (3) NW Solar system; planetary atmospheres, surfaces and interiors, the moon, comets. The solar wind and interplanetary medium. Formation of the solar system. Prerequisite: PHYS 224 which may be taken concurrently. ASTR 322 The Contents of Our Galaxy (3) NW Introduction to astronomy. Basic properties of stars, stellar systems, interstellar dust and gas, and the structure of our galaxy. Prerequisite: PHYS 224 which may be taken concurrently; PHYS 225 which may be taken concurrently. ASTR 323 Extragalactic Astronomy and Cosmology (3) NW Galaxies, optical and radio morphology and properties. Clusters of galaxies, radio sources, and quasars. Observational cosmology. Prerequisite: ASTR 322 which may be taken concurrently. ASTR 421 Stellar Observations and Theory (3) NW Observations and theory of the atmospheres, chemical composition, internal structure, energy sources, and evolutionary history of stars. ASTR 422 Interstellar Material (3) NW Description and physics of the matter between the stars. Physical conditions, distribution, evolution, and motions of interstellar atoms, molecules, and dust grains. Exchange of energy and matter between stars and interstellar material. ASTR 423 High-Energy Astrophysics (3) NW High-energy phenomena in the universe. Includes supernova, pulsars, neutron stars, x-ray and gamma-ray sources, black holes, cosmic rays, quasi stellar objects, active galactic nuclei, diffuse background radiations. Radiative emission, absorption processes, and models derived from observational data. Prerequisite: PHYS 224; PHYS 225. ASTR 480 Introduction to Astronomical Data Analysis (5) NW Hands-on experience with electronic imaging devices (CCDs) and software for image reduction and analysis. Introduction to operating systems, reduction software, and statistical analysis with applications to CCD photometry. Prerequisite: ASTR 323, which may be taken concurrently. ASTR 481 Introduction to Astronomical Observation (5) NW Theory and practice of obtaining optical data at a telescope. Preparation, obtaining data with a CCD on a telescope, and subsequent data analysis for completion of a research project. Prerequisite: ASTR 480. ASTR 497 Topics in Current Astronomy (1-3, max. 9) NW Recent developments in one field of astronomy or astrophysics. Prerequisite: either ASTR 101 or ASTR 150, either of which may be taken concurrently. Instructor Course Description: Ana M. Larson David C. Catling ASTR 499 Undergraduate Research (*, max. 15) Special astronomical problems and observational projects, by arrangement with instructor. ASTR 500 Seminar in Elementary Astronomy Instruction (3) Seminar in the preparation of lecture and workshop materials with emphasis on demonstration, visual aids, and the evaluation of students' progress. Credit/no credit only. Instructor Course Description: Ana M. Larson ASTR 507 Physical Foundations of Astrophysics I (3) Thermodynamics from an astronomer's point of view: black body radiation, basic radiative transfer, equation of state, degenerate gases, crystallization at high density. ASTR 508 Physical Foundations of Astrophysics II (3) Introduction to astronomical hydrodynamics and magnetohydrodynamics, basic theorems and application to stellar and interstellar magnetic fields. Introduction to plasma physics, waves in a plasma. ASTR 509 Physical Foundations of Astrophysics III (3) Potential theory as applied to astrophysical systems. Orbits. Integrals of motion. Equilibrium and stability of stellar systems. Encounters of stellar systems. Kinetic theory of collisional systems. Applications of stellar dynamics to star clusters, galaxies, and large-scale structure. ASTR 510 Nuclear Astrophysics (3) Big bang nucleosynthesis; nuclear reactions in stars; solar neutrinos and neutrino oscillations; core-collapse supernovae; nucleosynthesis in stars, novae, and supernovae; neutron starts; composition and sources of cosmic rays; gamma ray bursts; atmospheric neutrinos. Offered: jointly with PHYS 554; A. ASTR 511 Galactic Structure (3) Kinematics, dynamics, and contents of the galaxy. Spiral structure. Structure and evolution of galaxies. ASTR 512 Extragalactic Astronomy (3) Types of galaxies. Integrated properties, content, and dynamics. Extragalactic distance scale, groups and clusters. Radio sources. Observational cosmology. ASTR 513 Cosmology and Particle Astrophysics (3) Big bang cosmology; relativistic world models and classical tests; background radiation; cosmological implications of nucleosynthesis; baryogenesis; inflation; galaxy and large-scale structure formation; quasars; intergalactic medium; dark matter. Offered: jointly with PHYS 555. ASTR 521 Stellar Atmospheres (3) Theory of continuous radiation and spectral line formation. Applications to the sun and stars. Prerequisite: PHYS 421 or equivalent. ASTR 522 Stellar Atmospheres (3) Theory of continuous radiation and spectral line formation. Applications to the sun and stars. Prerequisite: PHYS 421 or equivalent. ASTR 523 Solar Physics (3) Sun as a star, solar photosphere and outer convection zone, granulation and related phenomena, solar chromosphere, and corona, solar activity (especially sunspots and solar flares), sun's radio emission, solar-terrestrial relations. ASTR 531 Stellar Interiors (4) Physical laws governing the temperature, pressure, and mass distribution in stars. Equation of state, opacity, nuclear energy generation, computational methods. Models of main sequence stars and star formation. Prerequisite: PHYS 421 or equivalent. ASTR 532 Stellar Evolution (3) Theoretical and observational approaches to stellar evolution. Structure of red giants, supernovae, and white dwarfs. Observations of star clusters and the chemical composition of stars as they relate to the theory of stellar structure. Prerequisite: ASTR 531. ASTR 541 Interstellar Matter (3) Physical conditions and motions of neutral and ionized gas in interstellar space. Interstellar dust, magnetic fields, formation of grains, clouds, and stars. Prerequisite: modern physics or permission of instructor. ASTR 555 Planetary Atmospheres (3) Problems of origin, evolution, and structure of planetary atmospheres, emphasizing elements common to all; roles of radiation, chemistry, and dynamical processes; new results on the atmospheres of Venus, Mars, Jupiter, and other solar system objects in the context of comparative planetology. Offered: jointly with ATM S 555/ESS 581. ASTR 556 Planetary Surfaces (3) Comparison of surface processes and conditions on Mercury, Venus, Earth, moon, Mars, asteroids, and satellites of the great planets. Emphasis on understanding how and why planetary surfaces differ from one another and the implied course of solar-system evolution. Analysis of data from Earth-based telescopes and manned and unmanned space missions. ASTR 557 Origin of the Solar System (3) Nebular and nonnebular theories of the solar system origin; collapse from the interstellar medium, grain growth in the solar nebula, formation of planetesimals and planets, early evolution of the planets and other possible planetary systems; physical and chemical evidence upon which the ideas concerning the origin of the solar system are based. Offered: jointly with ESS 583. ASTR 561 High Energy Astrophysics (3) Observed properties of supernovae, x-ray stars, radio sources, quasars. Theories explaining such objects. Origin of cosmic rays. ASTR 575 Seminar in Astronomy (1-2, max. 20) Discussion of recent research in astronomy and astrophysics. Credit/no credit only. Prerequisite: permission of department. ASTR 576 Astronomy Colloquium (1, max. 20) Current research topics in astronomy and astrophysics. Credit/no credit only. Prerequisite: permission of department. ASTR 581 Techniques in Optical Astronomy (5) Theory and practice of obtaining optical data. Astronomical photoelectric photometers, spectrographs, interferometers, CCDs, and infrared equipment. Data-reduction techniques with emphasis on statistical analysis using digital computers. Observations with MRO thirty-inch telescope. ASTR 597 Topics in Observational Astrophysics (1-5, max. 20) . ASTR 598 Topics in Theoretical Astrophysics (1-5, max. 20) ASTR 599 Advanced Astronomy Seminar (1-3, max. 6) Practical exercises in astrophysics. Emphasis on methods and techniques of simulation, acquisition, evaluation, and analysis of observational data and its interpretation using models of astrophysical systems. Prerequisite: permission of instructor. ASTR 600 Independent Study or Research (*) ASTR 700 Master's Thesis (*) ASTR 800 Doctoral Dissertation (*) united nuclear Chemicals & Metals mmonium Nitrate chemical formula: NH4NO3 ( powder ) Ammonium Nitrate is an oxidizer now becoming popular in new rocket propellant mixes. Also used in our "Water Starts a Fire" formula in the Making Fireworks & Chemical Experiments section. Keep in a tightly closed container, it has a bad habit of absorbing moisture from the air and getting hard and chunky. 2 ounces $2.00 4 ounces $4.00 8 ounces $8.00 Ammonium Perchlorate chemical formula: NH4ClO4 ( powder ) A powerful oxidizer used in most modern composite Rocket Propellant formulations. Also used in special low smoke Colored Star formulas. 2 ounces $3.50 4 ounces $7.00 8 ounces $14.00 Bismuth Pellets chemical formula: Bi ( pellets ) Very high purity (99.99%) Bismuth metal in pellet form. Pellets weigh about 25 grams each. You won't believe the unusual things you can do with this stuff. Click on the graphic for more info... 4 ounces $5.00 8 ounces $10.00 16 ounces $18.00 Uranyl Acetate chemical formula: (CH3COO)2UO2 ( powder ) A radioactive Uranium compound. No use in pyrotechnics, but used in physics demonstrations & various radiation experiments. Caution Required: Uranyl Acetate is toxic and also radioactive. 5 gram bottle $20.00 Post apple scientific Quantity Name SKU Each Total Sodium Hydroxide, Pellets, ACS, 25g - 12 Pack PAS-C-7470-0025-12-N $40.39 Sub Total $40.39 Tax $0.00 Shipping $5.44 Total $45.83 Price Item # Description Information $21.95 #10080 Bat house Bats are beneficial creatures that help control pesty insects. Attract them with our Bat house Sharon Howell 2270 S. New Lothrop Lennon MI 48449 Birds N Butterflies.com How to make a fertilizer bomb Ingredients: - Newspaper - Fertilizer (the chemical kind, GREEN THUMB or ORCHO) Shultz liquid fertilizer or - Cotton - Diesel fuel Make a pouch out of the newspaper and put some fertilizer in it. Then put cotton on top. Soak the cotton with fuel. Then light and run like you have never ran before! This blows up 500 square feet so don't do it in an alley! Instead of the newspaper could try using plastic containers 30 gallon or 55 gallon containers and fill up containers with fertilizer. Can practice with 1 gallon plastic or glass bottles to see if it actually works. Hi I am single and I live in Kirkland about 20 minutes from Seattle to the north of Gig Harbor. Would you like to live in a long term relationship for the rest of your life with me as I can give my care, and love to you. Let me know if this is what you want? Do you like to cuddle, and make love? Do you like dancing? from, Robert. robrain@blarg.net Chapter 11 1997 Stephen J. Shawl. Permission to print one copy of these pages is granted only to purchasers of Discovering Astronomy by Robbins, Jefferys, and Shawl. Chapter 12 Telescopes There are two main types of optical telescopes: Refractors refract light through a lens to a focus point. Reflectors reflect light from curved mirrors to a focus point; all large professional telescopes today are reflectors. The main lens or mirror of the telescope is often referred to as the objective of the telescope. The distance from the lens or mirror to the point where light from an infinitely distant object focuses is the focal length. No optical system is perfect; such problems are called aberrations. Lenses have chromatic Aberration, which is when different colors of light focus at different points. This causes a blurred image. One way that this is overcome is by using another lens to bring the light together at the same focus. This is called using compound lenses; all good telescopes and eyepieces are compound. All spherical surfaces are subject to spherical aberration where light that strikes the mirror (or lens) on the outer edges come to a focus at a different point than the light that strikes the mirror (or lens) on the inner area. One way to overcome this for mirrors is to make in the shape of a parabola rather than a sphere. The problem the Hubble Space Telescope has was dur to spherical aberration. Properties of Telescopes: Light Gather Power (LGP) measures the ability of the objective to gather light compared with the human eye. It is given by Area of objective / area of eye ; which is approximated by D2 / (1/5) 2 = 25D 2 if D is measured in inches. Diameter LGP 1-inch 25 6-inches 900 8-inches 1600 27-inches 18,225 200-inch (5-meter) 1,000,000 4-inch (10-meter in Hawaii) 4,000,000 big telescopes are important because they allow us to see very faint objects. Resolving Power (Resolution) This is the minimum angular separation that can be detected between two objects. The smaller the minimum angular separation, the better. For example, the smaller the minimum separation, the more detail you can see when looking at Mars. Big telescopes are important because they allow us to resolve images that are really close together so detail can be better seen. However, the Earth's atmosphere blurs images because it is turbulent. in practice, the ability of a telescope to see detail is limited by the earth's atmosphere. This is why the Hubble Space Telescope is so important because it is above the atmosphere and is not affected by the distortion caused by it. Resolution is given by 4.56/D (inches) or 10/D(cm). The larger the objective, the better the telescope can resolve detail. This is the maximum resolution this objective can possibly give. Objective diameter Resolving Power 1-inch 4.5 seconds of arc 6-inch 0.76 seconds of arc 27-inch 0.17 Hubble Space Telescope (94-inch) 0.05 seconds of arc 200-inch 0.02 seconds of arc But, there is a practical problem, which is the Earth's atmosphere. The atmosphere's density changes with height. as light travels through it, the atmosphere acts like a lens and refracts the light. However, the atmosphere is like a moving lens that causes images to dance around. This effect of the atmosphere is called seeing. Typically, the seeing causes the image to spread to about a second of arc in size. Sometimes, in the best locations on Earth, the seeing is as small as 0.25 seconds of arc. The practical limitation of resolution is the Earth's atmosphere. For this reason, for telescopes larger than about 16-inches, it is not the limitations of the objective size but of the atmopshere that limits resolution. Only if a large telescope (size greater than about 16-inch) is above the atmosphere will the theoretically possible resolving power be met. Magnification It is defined as the Focal length of objective / focal length of eyepiece Telescope eyepiece can be changed, so magnification of telescope can be changed easily. Magnification is the least important property of a telescope (LGP is more important). Don't get suckered into buying one having a high magnification! That's what the stores usually try to push. Chapter 13 Spectroscopy (Chapter 13) A spectrum is the distribution of intensity with wavelength. It can be presented as a: 1) photograph--useful, but is does not allow for detailed analysis, or a 2) graph--much more useful in terms of analysis. The dips in the graphs correspond to areas that would be dark in a photograph. These are decreases of intensity of light-->known as dark lines. The bright lines in a photograph are areas of increasing intensity and are shown as peaks on the graphs. The graph representing a spectrum often has a huge range of intensity. The large intensity range cannot be presented adequately with a "normal" graph, in which each mark on the axis represents equal differences between values. (For example, if the number range from 1-100, the tick marks might be separated by, say, 10.) When we have a large range of numbers, for example numbers going from 0-106, rather than graphing the numbers directly we take their logarithm, which is the exponent of the 10 in scientific notation. Such a graph using a logarithmic scale is used to show a large range in numbers and is extremely useful. The graphs of spectra in the book are on logarithmic scales. These scales will be used in many places throughout the rest of the course, so you must learn to understand them. There are three types of spectra: 1) continuous spectrum 2) dark line spectrum 3) bright line spectrum We can begin to understand these types of spectra through Kirchhoff's Laws: 1) A luminous solid or liquid, or a gas at a high pressure, emits light at all wavelengths-->produces a continuous spectrum 2) A luminous rarefied (low density) gas emits light whose spectrum shows a bright line spectrum-->produces an emission line spectrum 3) White light from a luminous source, when passed through a cooler gas, may be absorbed at certain wavelengths, giving a dark line spectrum or absorption line spectrum To understand these requires an understanding of the structure of the atom. Atomic Structure What does the atom look like? The model we use for atom's structure consists of a nucleus containing protons (positive charge) and neutrons (no charge), surrounded by the orbits of electrons (negative charge). The electrons can exist only in certain orbits that surround the nucleus. The laws of nature require that there are only certain orbits an electron can occupy. The orbit closest to the nucleus is called the ground state. Other orbits are excited states. An electron in inner orbit has less energy than an electron in an outer orbit. Therefore, energy is required to move an electron from an inner state to an outer state. This energy can come from light that is passing through the gas and striking the atom. The atom can absorb white light and move the electron to a higher energy level, producing a dark line spectrum. Energy of upper state = energy of lower state + energy Absorption Spectra Electrons can change orbits, but the closer the electron is to the nucleus, the less energy it has. Therefore, some amount of energy is needed to move the electron to an outer orbit. This energy can come from the light that passes through the gas containing the atom in question. Energy is absorbed having an amount exactly equal to the amount of energy needed to move the electron to a higher orbit. The amount of energy needed to move the electron can be expressed using this equation: E = hf = hc/ From this equation, we see that the amount of energy removed from the beam that passes through the gas determines the wavelength of light that is absorbed. Since the photon has been removed from the incident beam of light (by being absorbed), the light has been removed, and dark lines will appear on the spectrum. an absorption spectrum occurs when an electron goes from a lower orbit to a higher orbit. Absorption spectra cannot occur without a continuous spectrum. There must be a continuous spectrum to have energy to absorb. Emission Spectra Electrons can also go from outer orbits to inner orbits. As electrons move closer to the nucleus, they give off energy that appears as photons. Once again, the amount of energy can be determined using E=hf=hc/. An emission spectrum will be observed when an electron goes from an outer state to an inner state. Note: Atoms can be excited to a higher state and then fall down to a lower state through emission. Spectra and Different Elements Each element has its own, unique number of protons; that, in fact, is what differentiates one element from another. Protons have a positive charge and the number of charges you have (along with number of neutrons) determines where the electron orbits are within atoms. As you change the number of charges, you also change the amount of energy it takes to move from one orbit to another, which changes the location of the emission and absorption lines on a spectrum. Therefore, each element will have a different spectrum; each is unique. Because elements have unique spectra, we can determine what elements are present in stars by analyzing their spectra. This allows us to distinguish elements by the patterns of lines that are present. The Spectrum of the Sun The spectrum of the sun shows a continuous spectrum with an absorption spectrum on top. We can conclude from this observation that the sun is composed of a hot gas surrounded by a cooler gas. We find that the region surrounding the Sun (called the chromosphere and corona, which are observed during total eclipses) rises to temperatures of millions of degrees; the spectrum of the corona is an emission spectrum. The model of the Sun includes a high temperature, low density gas surrounding the rest of the Sun. To better understand how spectra work, we need to look at the concept of energy levels. For this discussion, you need the figures in your book and those shown in class. Energy Levels The energy required to move an electron from the first excited to the second excited state is not as great as the energy required to move the electron from ground state to the first excited state. This is because the electron is not held as tightly to the nucleus as when it was in ground state, so less energy is required to make a transition. The energy level diagram shows the energy required to move from one orbit to another. As you move further out, the levels get closer together because they involve smaller amounts of energy. The amount of energy given off as the electron drops from the fifth to the first levels equals the length of the line shown on the energy level diagram, and corresponds to the wavelength since E=hf=hc/. If a photon drops from the fifth level to the second level, the electron will not lose as much energy and will have a longer wavelength than the photon which moved from the fifth level to the first. Similarly, a photon which moves from the fifth level to the third will have yet less energy than the other two and will have a longer wavelength. Hydrogen Spectrum All the transitions that go down to the ground state are known as the Lyman series. They occur in the ultraviolet region. The transitions that involve the first excited state are the Balmer series. These occur in the visual part of the spectrum. The transitions that involve the second excited state are known as the Paschen series and are in the infrared part of the spectrum. The transitions that involve the third excited state are known as the Pfund series. (Because the Balmer Series ocurs in the visual part of the spectrum it's the most important one.) We understand the continuous spectrum by studying something we call a black body. A black body is a fictitious (hypothetical) body that astronomers use to compare with real bodies. We use the black body concept because we can easily understand their properties and because stars are roughly similar to them. A black body absorbs all the radiation that falls on it and reemits the absorbed energy over all wavelengths (continuous spectrum). a blackbody spectrum is a continuous spectrum. (NOTE: A black body has nothing to do with black holes!) The spectrum of a black body depends only on temperature. It does NOT depend on chemical composition as is the case for the line (absorption and emission) spectrum. We looked at the spectra of black bodies having different temperatures. From these are able to conclude a few important items: All bodies of temperature greater than 0 K emit energy at all wavelengths. Wien's Law- The wavelength at which the spectrum is at it's maximum intensity times the temperature equals a constant. Expresssed mathematically, this is max T = constant max is the wavelength at which the intensity is greatest. T is the temperature of the black body. This tells us that the hotter the body is, the shorter its maximum wavelength will be. This gives us a method for determining the temperature of stars through detecting their maximum wavelength. In other words, hot bodies are bluish/white while cool bodies are reddish. Because stars are rough approximations to a blackbody, we can apply Wien's law to them to determine its surface temperature. Since a spectrum is a graph of the energy emitted by the body at each wavelength, the area under the curve of spectrum (intensity vs. wavelength) is the total energy emitted per square inch per second by a body of that temperature. This is known as the Stefan-Boltzman Law, which we express more precisely as follows: The energy emitted per area per second is proportional to the temperature to the 4th power, i.e. E ~ T4 Example: How much more energy than the Sun (6000 K) does each area of a 48,000 K star radiate? Estar / Esun = [ Tstar / Tsun ] 4 = [48,000 / 6000] 4 = 8 4 = 4096 Summary of black bodies: The continuous spectrum depends only on temperature not on chemical composition. Wien's law: max T = constant Stefan-Boltzman law: E ~ T4 Summary of Spectra (shown with an important diagram): Internal regions of a star produces a continuous spectrum. Outer regions of star is cooler and produces absorption lines. Interstellar space also produces absorption lines (primarily Calcium and Sodium). Earth's Atmosphere also produces absorption lines Observed Spectrum consists of the sum of these and is complex. Chapter 14 Stellar Spectra (Chapter 14) The first thing a scientist in any field of study does is to classify the objects of study. Biologists classify planets and animals; geologists classify rocks and minerals; astronomers classify stars. Stars can be classified in a variety of ways. For example, in the early 1900s a large number of stars had their spectra observed. It was observed that these spectra were not all different but fell into a relatively small number of groupings, where were called spectral types or spectral classes. We will start by examining the spectral types to see what they were based on. Once we see the observational basis for the classification, we will work at understanding why stars have spectral that differ in appearance. One part of the history is valuable here. The spectra obtained, which numbered in the hundreds of thousands, were classified by Annie Jump Cannon at Harvard. Her work provided the basis of most of the work done by astronomers for the rest of the century! Her work is still used today, although it is being redone using more modern observations by Nanch Hauk at the University of Michigan. The Observational Basis of Spectral Classification Most stars have only absorption lines on top of a continuous spectrum; emission lines are relatively rare. whenever you observe a spectrum of a "normal" star, keep in mind that the lines will be obsorption lines. This statement is important because sometimes photographs show absorption lines to be dark while others may show them to be bright! This differences comes about because sometimes negative images are shown while othertimes positive images are shown. In chapter 134 of your text, absorption lines are all dark except in figure 14-18. The spectra of stars have been placed into groups that are designated by latters: O, B, A, F, G, K, M. Originally they were in alphabetical order, but that order was not meaningful. Once the spectral classes were better understood, it became possible to subdivide the classes further by placing numbers next to the letter. you can have stars of spectral types B0, B1, B2, B3, B4, B5, B6, B7, B8, and B9; the same is true for the other letters (but in practice, some numbers are skipped for some letters). These classifications come about because the spectra display different characteristics in their spectra. Spectral Types and their characteristics Spectral Type Observed characteristics O ionized helium, neutral helium, hydrogen present but not terribly strong B no ionized helium, neutral helium, hydrogen stronger A hydrogen strongest F hydrogen weaker, some metals G hydrogen weaker, metals, G band (caused by molecules) K metals dominate M Many spectral lines; molecules strongly present What determines these different observed characteristics? To answer this requires understanding two things: 1.Most stars are consist of 70% hydrogen, 28% helium, and 2% everything else. most stars are chemically very similar. 2.We saw in Chapter 13 that we can determine the temperature of a star from Wien's law. (Reddish stars are cool; blue or whitish stars are hot. In other words, the wavelength of maximum intensity depends on the wavelength.) If we then plot temperature against spectral type, we find that temperature and spectral type are correlated. Applying energy level diagrams to spectra The lecture then proceded to discuss what the spectrum of a star should look like for stars of different temperatures; this was similar to the discussion in the text. The discussion requires understand the energy level diagrams first discussed in Chapter 13. Things We Can Determine Using Spectra 1. Atmospheric Density (Pressure) The "body" of a star is surrounded by cooler gases that produce absorption lines. The gases have a mass, which means they have a density and pressure. Spectral lines are often described in terms of their line profiles. These can be narrow, wide and deep, or shallow and broad. When a transition occurs between energy levels, a spectral line forms. If other atoms are around, they will bump into each other causing the energy levels to change slightly because the atoms are perturbed by the other atoms. When you have a large collection of atoms, the energy levels can be changed slightly. in a large collection of atoms, each will have slightly different energy levels. Transitions will occur from one slightly changed energy level to another slightly changed energy; spectral lines will therefore be at slightly changed wavelengths. The end result for a gas having large numbers of atoms is that instead of having narrow spectral lines formed, they will be considerably broader. If you have 2 stars of the same temperature but different size, atoms in the smaller star will interact more often than the atoms in a larger star. spectral lines will be broader in small stars than they are in larger stars. one can say something about the size of a star from looking at the appearance (broad/narrow) of spectral lines of hydrogen. 2. Chemical Composition Usually this is about the same for all stars; however, there are some differences between a small fraction of stars. Some have bands and lines of carbon. Some have "strange" chemical elements present in them. These things can be seen in the stellar spectra. 3. Abundances The abundance of different elements in stars can also be determined. It was Cecelia Payne-Gaposchkin who first proved that stars are mostly hydrogen. 4. Motions of stars Consider a wave emitted by a stationary source. Drop a pebble in water and it will make a wave. Tap the water each second and more waves will occur but the distance between the waves will be constant (with a frequency of 1 per second). If the source is moving, however, an observer will not see uniform distance between the waves. Depending on where the observer is, he/she will see either shorter wavelengths or longer wavelengths. If the wavelengths appear to be shorter, the waves are said to have undergone a blueshift. If the wavelengths are longer, the waves have undergone a redshift. What the observer sees depends on the motion of the source relative to the observer. If it's moving away, the shift is red; if it's moving toward, it's blue. The observed change of wavelength due to the relative motion of the source and an observer is called the Doppler Effect or Doppler Shift. If the source is moving perpendicular to the line between it and the observer, there will be no Doppler shift. The source is moving neither toward nor away from the observer; consequently, the observer will not observe a shift. If the source and observer are moving at some arbitrary angle, part of the motion (a component of the motion) will be toward/away from the observer so there will be a "partial" shift. By "partial" we mean it will be less than would be the case if the object were moving directly toward/away from the observer. The Doppler Effect is defined as an observed change in frequency or wavelength when you have a relative motion between a source and an observer. We can determine how fast something is moving using the following formula for the Doppler shift: V / c = is a single symbol representing the change in wavelength wavelength it would have if it were not moving (called the rest wavelength) c = speed of light V = radial velocity (radial meaning toward or away---directly along the line of sight.) The change in wavelength and the rest wavelength are observable in spectra, and the speed of light is known, which means that we can calculate the speed with which the object is moving. Example: If a spectra is normally at 6000 angstroms, and it is observed at 6200 angstroms, what is the radial velocity for this star? Answer: (200) (3 x105 km/sec) / 6000 = (6x107 ) /6 x 103 = 104 km/sec. 5. Rotation Gases from different places on a rotating star will be Doppler shifted; gases rotating away from an observer will be redshifted while those rotating toward the observer will be blueshifted. rotation causes spectral lines that are broad and shallow. Measuring the width of the spectral line allows us to measure how rapidly the star rotates. 6. Turbulence In a star that is highly turbulent, there are areas where gases are going down and areas where gases are rising. The rising gases are blueshifted (toward you) and the falling gases are redshifted (away from you). This broadens the spectral lines. Now we see that there are three conditions which can cause broadened spectral lines. They can be caused by density, rotation, and turbulence; however, the details in the profiles will differ among these so we can distinguish what's happening. 7. Magnetic Fields When an atom is placed into a magnetic field, its energy levels change. They are split; where before there was a single energy level, now there can be 2, 3, 4, .. Therefore the transitions that occur between these multiple levels result in a more spectral lines being produced. The stronger the magnetic field, the more spectral lines are present due to an increased splitting of the energy levels. The Zeeman Effect is the term used to indicate the splitting of spectral lines caused by the magnetic field. By measuring how far apart the lines are, we can determine how strong the star's magnetic field is. 8. Shells Rings of gas that surround stars can change the stellar spectra. The normal spectrum of a star is a continuous spectrum with absorption lines that may be broadened due to rotation. The light from the edges of a ring will be an emission because the ring is hotter than the material behind it along the line of sight, which is cold, empty space. The part of the ring directly in front of the star will cause an absorption line because it is cooler than the star behind it. By measuring the distance between the lines and by using the Doppler shift formula, we can determine how fast the ring is expanding. Spectrum of the Sun The spectrum shows a continuous spectrum with hydrogen, magnesium, iron, and sodium absorption lines. There are no emission lines present in the normal solar spectrum. However, if you block out the light of the photosphere, you will see the corona, which shows an emission spectrum of highly ionized gases; the corona is a low density high temperature gas. Chapter 15 Properties of Stars (Chapter 15) Distances to Stars Review of Angular Size formula Angular Size= 57.3 true size / distance Review of Parallax Parallax angle = 57.3 x 1AU / Distance in AU Distance in AU = 57.3 x 1AU / Parallax angle This allows us to calculate the distance to a star in AU. If you express the parallax angle in seconds of arc rather than degrees, the formula can be expressed like this: Distance (parsecs) = 1 / parallax A parsec is the distance to a star whose parallax is one second of arc. 1 pc = 3.26 ly Distance (ly) = 3.26 / parallax (seconds of arc) The important thing is to understand that the smaller the observed parallax, the greater the distance. Example: What is the distance to a star having a parallax of 0.76 seconds of arc? d = 1/p d = 1/0.76 = 1.33 parsecs d = 1.33 pc x 3.26 ly/pc = 4.3 ly This method can only be used for stars that are relatively nearby. The smallest parallax angle we can measure is about 0.01, so the greatest distance measurable, using this method, is 1 / 0.01 = 100 pc or 300 ly. In order to determine distances that are further away, we have to use different methods. A tremendous advance in parallax measurements occurred recently with the HIPPARCOS mission, which measured parallaxes for some 120,000 stars to an accuracy of 0.001 seconds of arc, and a million stars to 0.020-0.030 seconds of arc. The HIPPARCOS Mission has published some 3-D images of star fields that you can look at on the screen using the 3-D color classes in your Activity Kit! In looking at these, be sure the red is on the left side. Furthermore, if you don't see it right away, keep looking; your eye's will relax and accomodate. Once they do, it's pretty neat!! Ursa Major Cygnus and Lyra Cassiopeia Scorpius A future project in the works, GAIA, will observe parallaxes for a billion stars! Distance and Brightness Brightness indicates the number of photons that pass through a unit area. The further away an object is, the dimmer it appears. This can be expressed in the Inverse Square Law of Light: B(r) L / r2 B(r) = apparent brightness at r L = luminosity (energy/sec); this is really number of photons emitted per second r = distance Binary Stars and the determination of stellar mass Visual Binary stars: can see motion of one star relative to another. From this we can, over time, get the period of motion, and the angular semi-major axis. Then if we know the star's distance, we can get the true semi-major axis (by using the angular size formula, which you now know and love!) For visual binary stars for which we have the distance, we have P and A. Given these, we can use Newton's modification of Kepler's third law to get the sum of the masses of the 2 stars: (M1 + M2)= A3 / P2 (As asked by one student in class during a previous semester, by observing the motion of each star around the center of mass of the 2 stars, you can get the ratio of the masses M1/ M2 from which one can then get the individual masses.) Spectroscopic binary stars: these stars cannot be resolved individually. However, their motion can be seen because of the periodic motions of the spectral lines in the spectrum. From a graph of the Doppler shift with time, we can get the ratios of the masses of the two stars, M1/M 2. Eclipsing binary stars: In this case, we are seeing the orbit edge-on and an eclipse occurs. If an eclipsing system is also a spectroscopic binary, then we can get the masses of the individual stars. Furthermore, in many cases we can also determine information about the diameters of stars. Summary: the main thing here is that information on stellar masses and diameters (especially masses) come from the study of binary stars. Correlations Between Stellar Characteristics Now that we have determined a number of properties of stars: apparent brightness, color, temperature, speed, magnetic field, atmospheric pressure, density, and luminosity. We can now look for coorelations between various quantities. In particular, for the nearby stars we know temperature and luminosity (because we know their distances from their observed parallax). For these stars, there is a correlation between the temperature of a star and its luminosity. A diagram of temperature and luminosity is called a Hertzsprung-Russell (or H-R) diagram. The nearest stars follow a well-defined path in the H-R diagram. This well-defined path is known as the main sequence. However, for the nearest stars, there is a group of stars hotter than the majority but a lot less luminous. These are the white dwarfs. If we consider the brightest stars in the sky (rather than the closest ones) we also find that the majority also fall along the main sequence, but there are other stars located in other well defined places (and no white dwarfs). The Hertzsprung-Russell (H-R) diagram graphs luminosity versus temperature. What, really, is luminosity? From the Stefan-Boltzman law, we know that E T4 (energy/second/area). If L = total energy coming out of the entire star, then L (energy/sec) = E x area. If the star is a sphere, the surface area of the star depends on the square of the radius, R2. Then the luminosity becomes L R2T4 This was used in class to explain why we have stars that are giants and others that are supergiants (in comparison to the dwarf stars). The dwarfs, giants, and supergiants are often referred as a luminosity class. Finding the luminosity class helps us to find the star's luminosity, which is really useful (see below). White dwarfs are hot stars that fall far below the main sequence. White Dwarf Density Density= Mass / volume = M / R3 The density of the sun is sun=1.4 gm/cm3 The mass of white dwarf = 1Msun The size of white dwarf = 0.01Rsun = 1Msun / (10-2)3 = 106 sun OR, = 1.4 x 106 gm/cm3 Expressed in units you are more used to, the density of a white dwarf is = 40,000 lbs/in3 The stars at the lower end of the main sequence have smaller masses than those higher up. The main sequence is a sequence of stars of ever increasing mass. As the mass increases, the luminosity also increases. This relationship between mass and luminosity (called the mass-luminosity relation), is valid only for main sequence stars; it is important and will be returned to in a later chapter. Remember that there is a relationship between luminosity, temperature and radius: L R2T4 This relationship can also be expressed in terms of the luminosity, temperature, and radius of the sun: L / Lsun) = R2/ R2sun T4 / T4sun Example: Suppose we observed a star to have a spectral type of A0. The star is observed to be 8 x 10-11 fainter than the sun. Furthermore, its's parallax is observed to be 0.01 seconds of arc. What is the star's luminosity? How large is the star? From the inverse square law of light we have: B(r)=L/d2 The star's distance is d(ly) = 3.26/0.01 = 326 ly = 2 x 107 AU B(r)=8 x 10-11 B(sun) From here, we can determine the luminosity: B(r)=L/r2 L=B(r)r2 L=(8 x 10-11)(2 x 107)2 L=32,000 L(sun) This star emits 32,000 times as much energy per second as the sun does! We can also determine the radius of the star: L / Lsun) = R2/ R2sun T4 / T4sun The spectral type of A0 tells you the temperature: T=12,000 K = 2T(sun) Then, we have 32,000 = R224 R2=2000 R=45R(sun) Using all this information, we can locate the star on the H-R diagram and determine that it is a giant! The H-R Diagram and Stellar Distances We can also use the H-R diagram to determine distance to a star: remember that B(r) = L/r2 . We observe B(r). If we can find L, we can then find r. There is a way of determining luminosity in the H-R diagram. Remember, we determine the temperature from the observed spectral type. Inother words, the spectrum tells us where the star is horizontally in the H-R diagram From the spectrum we can determine if the star is a dwarf, a giant, or a supergiant. We do this by seeing if the spectral lines are narrow or broad: if narrow the star is a supergiant; if broad, a dwarf. In other words, the spectrum can also tell us where vertically the star is in the H-R diagram. We can now use the H-R diagram-->again, the temperature tells us where the star lies horizontally while the width of the spectral lines tells us the luminosity class (dwarf, giant, supergiant). From this we can infer the luminosity. Then, given luminosity and the apparent brightness, we ge the distance. This is called the spectroscopic parallax method-->if you determine the brightness and luminosity using the spectrum, you can therefore determine the distance. This is important because it can be used to find the distance to any star for which you can obtain a spectrum. That a bunch! Here's a summary of the process. (It's really the same as figure 15-12 in the text!) Chapter 16 Stellar Structure and Evolution What are the concepts that allow us to understand the structure of a star? --The Sun has been the way it is now for a very long time. The Sun is in a state of equilibrium and so it does not change much. --What allows the Sun to do this? --The Sun consists of matter (hydrogen); this matter has mass and has gravity, which attracts other matter. The mass in the sun's center pulls on the mass farther out. one would expect that the sun would collapse if gravity were the only force acting on it. The Sun has not collapsed so there must be some other force activing to counteract gravity. This force is the outward gas pressure that is caused by the motions of the atoms in the gas. When the outward pressure of gas underneath equals the force of gravity we have hydrostatic equilibrium (a less technical term would be gravity-pressure equilibrium). --The gas pressure comes about because the star is so hot. Pressure is determined by the temperature of the surrounding gas. The relation between pressure and temperature is expressed in the Perfect Gas Law: P (approx) T --A star sits in space and loses energy. As it loses energy, it loses temperature. In order for a star to be in equilibrium, the energy produced must equal the energy lost-->this is referred to as thermal equilibrium. --If a star produces more energy than it loses, the temperature will increase, which then increases the pressure. An increase in pressure means that the gas will expand, causing it to cool off. The star contracts and returns to the state of equilibrium. How Energy is Produced Within a Star Two methods of energy generation 1) Gravitational Contraction: A large ball of gas has potential energy. It has the ability to transform the energy that's caused by gravity into something else. If you take something that has gravitational potential energy and make it collapse, you will produce energy. How long could the Sun shine, with the same brightness we see today, if its energy came from gravity? An analogy helps: consider a bucket of water that has a hole in it. How long will water remain in the bucket? It depends on the amount of water at the start, and the size of the hole (which determines the rate of loss of water). The time would be proportional to (mass of water) / (rate of water loss). In other words, t = M / rate. For a star, the time will depend on the amount of mass divided by the star's rate of energy loss, which is luminosity. t = E / L. Astronomers can calculate the amount of potential energy available, and we know the luminosity; we find that the lifetime would be short, only around 108 years. There is not enough potential energy in the Sun for its energy to have come primarily from gravitational collapse. We need some other mechanism for generating energy. 2) Nuclear Fusion: How much nuclear energy is there in the sun? Again, t = E / L. E is given by Einstein's famous formula, E = Mc2. Using this, as described in the text, we find that there is enough material in the Sun for fusion to make it remain in equilibrium for 1010 years. It makes sense that nuclear fusion might be a possibility for the source of energy in the Sun. In fact, it is strongly believed to be the source of energy for the Sun. The Processes that Produce Energy Proton-Proton Reaction The Sun consists of hydrogen that is ionized. Ionized hydrogen (hydrogen with no electrons) is simply a proton---a nuclear particle that has a positive charge. Since these protons have positive charges, they repel each other and will join together (fuse). To get them together to fuse requires that they overcome their natural repulsion. This will occur only if the temperature is high enough (about 10 million K) for the nuclei to move with high enough velocities (i.e. have a large enough kinetic energy) to overcome the electrostatic repulsion. Under these conditions of high temperature (and high density) the 2 protons will fuse and form deuterium. Deuterium is hydrogen, because it has only one proton in the nucleus, it also has a neutron. It is hydrogen but it is "heavy hydrogen". In addition to producing deuterium, the fusing of the two protons also produces a positron (a positive electron, i.e. antimatter, e+), and a neutrino (): 1)1H1 + 1H1 --> 1H2 + e+ + The subscript 1 is the number of protons in the nucleus; it is the atomic number. The superscript is the atomic weight, which is the number of protons + neutrons in the nucleus. The number of positive charges on the left side of the arrow equals the number of positive charges on the right side; this is always true. Similarly the atomic weights on the left and right must be equal. Keeping that in mind, you can determine which reactions are valid. Deuterium and another proton produce "light" helium and a gamma ray: 2)1H2 + 1H1 --> 2He3 + At this step, we have produced energy-->this is essentially the energy we see from the sun as visible light. Repeat both steps two times and two helium nuclei will be produced. When these are combined, "normal" helium and two protons are produced: 3) 2 He3 + 2 He3 --> 2 He4 + 21H1 The end result of what we have done is to take four protons and produced a helium atom, energy, neutrinos, and a positron. This cycle is often referred to as hydrogen burning (whereby hydrogen produces helium). This reaction is important in the Sun. Another type of hydrogen burning reaction occurs in stars more massive than the sun, where temperatures are greater than the 10 million needed for the p-p reaction. This is the CNO cycle. Keep in mind that the only way for fusion to occur is if the temperature is high enough for protons to overcome their electrostataic repulsion for each other and come together. This reaction is given in your text. Energy Transport There are three forms of energy transport: 1)Radiation transport-occurs by movement of photons 2)Convection-mass motion 3)Conduction-movement of electrons Radiation transport and convection are both important in stars like the Sun. Radiation transport occurs in the inner part of the Sun and convection occurs in the outer part. Conduction is not important in normal stars like the Sun, but it is important in white dwarfs and neutron stars. Radiation transport allows the gamma rays that are produced in the center to move out and be absorbed by atoms. They are then re-emitted at longer wavelengths and come out with less energy. Russell-Vogt Theorem The structure of a star in equilibrium is uniquely determined by the star's mass, chemical composition, and age. 2 stars having the same mass, chemical composition, and age will have identical interior structures. If you consider a group of stars having the same chemical composition and age, but different masses, the interior structures will be different. In particular, their surface temperatures and luminosities (i.e. the rate at which energy is lost) will be different. stars with different masses (but identical overall chemical compositions and ages) will be located in different places in the H-R diagram. we can use the H-R diagram to understand stars having different characteristics. Stellar Structure Model The above concepts can be expressed as complex equations, which are entered into a computer for solution. The solution of the equations is called a stellar model and is a table or graph that tells how the following quantities vary from point to point within a star: Temperature(r) Pressure(r) Density(r) Mass(r) Luminosity(r) Chemical Composition(r) Stellar Structure Model of the Sun A figure was shown in class (and is present in your text) showing the results of a such a model for the Sun. You should study these results to understand the interior structure of the Sun. Solar Neutrino Problem Neutrinos are particles that were originally thought to be massless particles, just as photons are massless. (That is, IF photons could be brought to rest, their mass would be zero). Also, neutrinos are without charge. Finally, their interact little with matter. They can travel through light-years worth of solid lead and not interact. The solar model, being a good scientific model, makes prediction of the number of the neutrinos expected from the Sun. We'd like to try to observe neutrinos from the Sun to see how the prediction compares with the observations. If one could detect neutrinos from the reactions in the Sun, one would be looking directly into the center of the sun, where the action is! How to do this? By building a neutrino telescope! Neutrinos sometimes do react with matter. For example, it is possible for a neutrino to interact with an atom of chlorine (Cl37 ) to produce argon (Ar37 ). We can make a telescope out of chlorine and examine it, after a while, to see if there are any argon atoms in the fluid. From this, one could then make a comparison of what is observed with what is expected from the model. Solar Neutrino Experiements Results: Many fewer than expected! This is problem (!) called the solar neutrino problem. It is one of the more important problems in physics and astronomy today (and for the past ~30 years). Why are there fewer then predicted? There are a variety of suggestions. 1. The models are wrong. As we'll see, however, there's good reasons not to think that they are in error (most everything else about the models seems right). 2. There is a theory in physics, that seems right in many ways, that predicts there to be 3 types of neutrinos. Neutrinos can oscillate (change) from one type to another. The "right" ones might be produced in the sun but then changed before reaching the Earth. The detectors may not be detecting the right kind of neutrinos. For this reason, many such neutrino experiments are now running, including the Davis experiment, the GALLEX experiment, the SAGE experiment, Super-Kamiokand e, and the Sudbury Neutrino Observatory. However, they are all finding too few neutrinos! 3. The Sun is filled with WIMPS, which are Weakly Interacting Massive Particles. (One of the conceivers of this idea is Ron Gilliland, a Kansan who was a student of mine in 1973/74.) The idea is that the universe is filled with these particles; being massive, they are attracted to stars. The interior contains these particles. In moving around, they carry energy away with them, cooling the interior of the Sun and decreasing the number of neutrinos produced. This theory also solves some other interesting astronomical problems. BUT, there's no observations or experiements showing that WIMPS exist!! Chapter 17 PRE-MAIN SEQUENCE EVOLUTION For a one solar mass star: The dynamical phase: A cloud of gas and dust will be made to collapse from one of a number of possible causes. A massive cloud might begin to collapse from its own gravity. Or, a nearby stellar exposion might produce shock waves that slightly compress the cloud and cause it to collapse (as you read in Chapter 6 is what we believe evidence shows us happened in the case of our solar system). Or, mass and energy loss from a nearby star might start the big squeeze, as observed in one case by the Hubble Telescope. Or, another cloud might collide with it. In any case, somehow a cloud begins to collapse. Only recently has a prest ellar core been observed! The inside collapses faster than the outside and begins to heat up. The inside region becomes warmer than the outside region. As it collapses, the density increases, and as gravity pulls it in, the pressure builds up so that it can no longer increase. The outward pressure becomes greater than the inward pressure, it "bounces" and begins expanding. The core expands and the outer part contracts. Gravity slows down the interior expansion and the whole protostar begins to collapse again. The density again increases, pressure builds up, and another bounce occurs. The inner part of the protostar expands outward again and by now the temperatures have increased so that the surface temperature is around 1,000-2,000 degrees. The protostar is now luminous enough that it is visible in the H-R diagram. The star flares up to the location at #1 on the H-R diagram. When it is at #1 on the diagram (below), energy comes from the conversion of gravitational potential energy into heat and luminosity. It is contracting and is completely convective, but no nuclear fusion occurs here because the temperatures are not hot enough. NOTE: The figures are highly schematic! The internal structure changes and therefore the luminosity and temperature change. There is less convection and more radiation transport. At point #2, there is no longer any convection. The surface temperature increases, the path in the H-R diagram changes. At point #3, the temperature has increased to around 10 million degrees. At this time, the temperature is high enough for fusion reactions to begin. What happens when Hydrogen Burning begins? Hydrogen-burning ignition produces energy, which then causes the cpre temperature to increase slightly. This increases the pressure, resulting in the slight expansion of the core (the core expands because it is a perfect gas), which then cools slightly. As the core slightly cools, this produces thermal and hydrostatic equilibrium. This means the contraction of the protostar stops. The star moves to point #4 , which as we will see, is on the main sequence. Stars unlike the Sun A 10 solar mass star will go through essentially the same process but it will evolve faster (the more massive a star, the faster it will evolve). A ten solar mass star will start in the general area of point #1. It is also convective and it starts moving down the path, but it gets to its point #2 where it's no longer convective, but radiative, at a much more luminous point. Its direction in the diagram changes much more rapidly. It will get to the main sequence much more quickly than the sun and it will have a higher surface temperature and a higher luminosity than did the sun at its point #4. A star of 0.5 solar mass also begins around point #1. It is completely convective. It moves along the same path as the sun for a while, but because it is less massive, the changes take much longer to occur. It continues past where the sun turned off, and keeps moving down until it is no longer convective, but radiative, and its path changes. Hydrogen burning begins, contraction stops and it ends up on the main sequence at lower temperature and luminosity. A star less then 0.08 solar masses will begin at #1 but it will never get to the point where its core temperature is high enough for fusion to begin. It cannot become a regular star, and instead becomes a brown dwarf, an object whose mass is so low it can never burn hydrogen or gain energy by fusion, so it eventually cools off and dies away. (another one, too!) When you have stars of different masses, they evolve to a point where they are all getting their energy from hydrogen fusion into helium. They all fall along the line indicated in the diagrams. This line is known as the Zero-Age Main Sequence (ZAMS). This is the line on which stars fall that are all getting their energy from conversion of hydrogen into helium, and are all at hydrostatic equilibrium. The main sequence is the region containing stars that are all obtaining their energy from hydrogen fusion. The main sequence is a mass sequence, where low mass stars have low (T,L) and high mass stars have high (T,L). Stars more massive than the sun do not get their energy from the proton-proton cycle but from another one called the Carbon-Nitrogen-Oxygen (CNO) cycle. This reaction is given in your book; you do not need to memorize it. The main thing is that it occurs at the higher temperatures possible in more massive stars, that it produces energy, and it is able to synthesize yet new elements. Main Sequence Lifetime The main sequence lifetime is much longer than the pre-main sequence lifetime. Lifetime=energy available luminosity Energy available=Mc2 t=1010M/L The mass-luminosity relation tells us that LM4. Therefore, t=1010/M3 This shows that the more massive a star is, the shorter its lifetime. Time Scales to point the ZAMS Mass (in solar units) Spectral Type Time to ZAMS (in years) 30 O6 30,000 10 B3 300,000 4 B8 1 million 2 A4 8 million 1 G2 30 million 0.5 K8 100 million 0.2 M5 1 billion Observations relevant to pre-main sequence evolution A star cluster is a grouping of stars located together in space and gravitationally bound together. For all the stars in a cluster: 1. The distance is the same. 2. Chemical composition is the same. 3. They formed at the same time-->have same age. If all the stars have these in common, then they must differ in mass; otherwise, they would all be identical. Remember that there is an important difference between the evolution of stars with different masses: the time it takes for them to evolve. In class was shown an H-R diagram for a star cluster, with the stars all essentially at point #1. Let's suppose at this point, time=0. Allow some time to go by. After 5,000 years passes, the more massive stars pull away from the line. As more time goes by, the most massive stars will have reached the ZAMS, the medium mass stars will have moved towards it, and the lower mass stars will not have moved much at all. This gives us a tool to see what stars are doing. If you look at a variety of star clusters and draw their H-R diagrams, and then find some clusters whose H-R diagrams look like the above, this tells us that the ideas of stellar evolution make sense because what we observe agrees with what we expect theoretically. It also allows us to determine the age of clusters because we can see how long it takes the cluster to look as it does in the H-R diagram. Star clusters often include various types of stars. One type of important is the T Tauri star: T Tauri Stars 1.variable stars 2.mass loss is observed 3.mass accretion is also observed 4.Lithium, which usually indicates youthfullness in stars, is observed 5.they are located above ZAMS in the H-R diagram of clusters We look at the H-R diagram for a cluster having stars on the upper (high temperature, high luminosity) end of the main sequence; the cooler stars were all above the main sequence, as were the T Tauri stars. The Cone Nebula of gas and dust is a region of star formation that also contains T Tauri stars, as well as new stars found by the Hubble Telescope. Stars form from gas and dust. Dust surrounding a protostar will be heated somewhat until it radiates. Being cool, it will radiate in the infrared. we can hope to "see" stars forming by looking for infrared radiation, which is able to penetrate the surrounding dust in a cloud. In looking in the IR, we are able to observed infrared stars, which are often stars in formation. The ISO (Infrared Space Observatory) satellite observed star birth in the Trifid Nebula. HST has also observed IR stars in Orion. General views of the Milky Way made by ISO also show lar ge numbers of protostars. The rho Ophiuchi Cloud is also a hot bed of star formation. When stars form, rotation and the conservation of angular momentum produce discs surrounding the protostar. Processes occur that force mass from the object to be ejected perpendicular to the dusty disc forming what are called bipolar nebulae. These stars are also associated with objects called Herbig-Haro objects (HH objects, for short). These objects are produced when material ejected from the poles of a protostar into a bipolar nebular collides with other material and forms shock waves. Orion Region spread throughout Orion there are emissions from some molecules, showing us that there are very large molecular clouds that are present within the Orion region. These giant molecular clouds contain gases, dust, and bright sources of infrared radiation. This shows us that this is an area of star formation. As the protostar collapses, it warms up and heats the dust. The dust radiates in the infrared and the infrared can be observed. The main point of this is that there is material available for star formation in the giant molecular clouds, which are seen to be present in the Orion nebula. The Hubble image of the Eagle Nebula in M16 is one of the most fantastic images ever photographed by astronomers. It shows areas of star formation in a way never before seen! Brown Dwarfs Some have now been observed! These observations are consistant with theory. Miscellaneous observations related to star formation: The Hubble telescope has been make many observations of importance to our understanding of star formation (such as the discovery of "proplyds", the discovery of EGGS, starbirth in a neighboring galaxy, and starbirth in a dim galaxy. Chapter 18 Post-Main Sequence Evolution The following figure is highly schematic and idealized for the evolution of a 1 solar mass star. The post-main sequence evolution begins at point #1 in the diagram, where the star is on the ZAMS. Its surface temperature is around 6,000 degrees. When in this position, there is a central core region converting hydrogen into helium, surrounded by a hydrogen envelope. Eventually, due to the conversion of hydrogen into helium, the internal structure changes. The luminosity increases, which means the star starts evolving away from the ZAMS, moving it to point #2. By now, approximately 4.5 billion years have passed and we're at the place in the diagram where the sun's located today. After a total of about10 billion years has passed, the point moves to point #3. At this point, the hydrogen is exhausted. A core of helium has formed; this core is known as an inert core because no nuclear fusion is going on. The core radiates away heat, but there is no more fusion going on inside because the temperature is now longer high enough. The star starts cooling off because it's losing energy. As it cools, the helium core contracts; while contracting it increases in temperature. Remember, core is still surrounded by a hydrogen envelope. As the core temperature increases, the temperature in the adjacent regions of the hydrogen envelope increases. The envelope is heated to the point where it reaches 10 million degrees, allowing for the hydrogen surrounding the core to ignite and begin hydrogen burning into helium. A hydrogen burning shell forms, producing photons and helium. The photons produced do not get out but push on the envelope, causing it to expand. (Without more photons getting out, the luminosity remains nearly constant after point #3.) After #3, the star expands and changes direction in the H-R diagram, toward #4. It cools and increases in size, and gets to the point where the star expands enough so that the star's atmospheric density is low enough for the photons to get out without being absorbed. (There is no #5 in this description!) Since there are now more photons getting out, luminosity increases and the star moves to #6 in the H-R diagram. At this point, the star has become a red giant. It is now 10-50 times larger than before. The surface temperature decreases to ~3,000 degrees while the envelope expands. All this time, the core has been collapsing. While it has been collapsing, it's been getting hotter. As it's been getting hotter, the density in the core has increased. The character of the core changes now. The core had consisted of ideal gases, but as the core collapses, it changes in to a degenerate gas. A degenerate gas is one whose pressure does not depend on temperature. The structure of the star is now composed of a collapsing degenerate helium core, surrounded by a hydrogen burning shell, surrounded by a hydrogen envelope that is expanding. The temperature in the core increases and reaches 100 million degrees. At this point, fusion can occur that involves helium burning. This is known as the Triple Alpha Reaction: He + He + He --> C Events following from ignition of helium in a degenerate core: In an Ideal Gas In a Degenerate Gas Energy generation leads to Energy generation leads to increased temperature, which causes increased temperature, which causes increased pressure, which causes increased energy generation, which causes expansion, which causes increased temperature, which causes cooling, which increased energy generation, which causes stops the star's contraction increased temperature, which causes increased energy generation, which causes increased temperature, which causes increased energy generation, which causes etc..., which causes BOOM (Helium flash)! In a degenerate gas, no adjustment occurs inside. Pressure builds up and the core explodes. This is known as the helium flash. The structure of the star is now a helium-burning core, surrounded by a hydrogen-burning shell, surrounded by a hydrogen envelope. After the explosion, the hydrogen-burning shell is disrupted--> luminosity decreases. The core is no longer degenerate--it goes back to a perfect gas. The core eventually collapses, temperatures rise again, and when they reach 100 million degrees again, helium-burning begins. This time, however, it is in an ideal gas--there is no helium flash because the pressure can adjust. The end result of this is a core burning helium into carbon, surrounded by the hydrogen-burning shell, surrounded by the hydrogen envelope. The star is now at point #7 in the H-R diagram. At this point, helium-burning occurs in a perfect gas. energy produced in the core increases as the hydrogen shell decreases in importance. The star evolves at a constant luminosity, moving it from point #7 to #8 in the H-R diagram. At point #8, the star has an inert carbon core, surrounded by helium, surrounded by the hydrogen-burning shell, surrounded by the hydrogen envelope. The core temperature decreases, its pressure decreases, and the inert carbon core starts to collapse. Temperatures then increase, and the temperature of the helium surrounding the core also increases. The helium gets hot enough to ignite helium-burning again. The structure now consists of a collapsing carbon core, surrounded by the helium-burning shell, surrounded by the helium envelope, surrounded by the hydrogen-burning shell, surrounded by the hydrogen envelope. The star moves towarrd point #9 in the diagram. The evolution after this point is the subject of the next chapter and will be considered in the next lecture. Validity (from observations) for these theoretical ideas Start by looking at star clusters. Remember that there are certain assumptions made about the stars in star clusters. They are all of the: 1) same distance 2) same chemical composition 3) same age However, their masses are different. Observing the H-R diagrams allows us to determine certain things about the star clusters. We see that as time goes on, stars evolve off the main sequence. In addition, as clusters get older, the turnoff point from the main sequence gets lower and lower. If we look at star clusters and see the H-R diagrams agree with our theories, this verifies our ideas. It also allows us to determine the age of the star clusters. By looking at the location of the turnoff point, we can determine the age of the cluster and the stars. There are different types of clusters. The Pleiades is known as an open cluster because of its generally open appearance. However, there are other clusters known as globular clusters (Hubble globular cluster work) that look very different from the open clusters. Open clusters will have 100-1,000 stars, while globular clusters have between 100,000 and 1 million stars. Here are some additional differences between open clusters and globular clusters: Open Clusters Globular Clusters H-R diagrams look different H-R diagrams all look alike Open appearance Round appearance due to strong gravity Some are young, others are old All have low turnoff points, which means they are all old Binary Stars Two stars in a binary system can intereact with each other as they evolve. If, for example, one is more massive than the other, the more massive one will become a red giant while the other is still on the main sequence. It is then possible for the red giant to transfer mass onto the main sequence star; such a transfer of mass modifies the mass of each star changing its future evolution. Chapter 19 Stellar Death For low-mass stars (M < 8 solar masses) When the star becomes a red giant, it becomes unstable and ejects its outer envelope. The ring-like object forms a Planetary Nebula with the object that ejected the ring near the center. (There are some spectacular Hubble Telescope results: 1, 2, and 3.) This object collapses until it becomes a white dwarf. The Sun will eventually eject a planetary nebula and then become a white dwarf. Hubble has even observed a newly formed planetary!! There's more, too! Planetary nebulae are thought to form from red giants. A forming planetary is called a protoplanetary nebula; the Egg Nebula is thought to be one. White Dwarfs are made up of degenerate material. Energy is transported by conduction in very dense material. The white dwarf has no source of energy other than what was already there. The properties of degenerate material were determined in the 1930s by Prof. S. Chandrasekhar, who received the Nobel prize in 1984 for his contributions to the studies of stellar evolution. One of the things he discovered about degenerate gases is a relationship between mass and radius. Mass-Radius Relation In white dwarfs, the greater the mass, the smaller the size. However, if the mass is larger than 1.4, the size goes to zero--it completely collapses down to nothing. This is called the Chandrasekhar limiting mass. Stable white dwarfs cannot exist if their mass is greater than 1.4 solar masses. How, then, does an 8 solar mass become a 1 solar mass white dwarf? By loosing mass. There are a variety of ways that stars can lose substantial amounts of mass. When stars are red giants, they can have stellar winds that cause the stars to lose large amounts of mass. An 8 solar mass star can decrease to 1.4 solar masses so that it can become a white dwarf after the ejection of its envelope. Depending on the mass of the star, it can go back up through the red giant phase and undergo more nuclear fusion. The Hubble telescope has actually observed a white dwarf that is inferred to have formed from a 7.6 solar mass stars. High Mass Stars (M>8 solar masses) The future evolution of mass stars, beyond the point of helium exhaustion in the core and the collapse of the inert carbon core, depends critically on the mass. The core collapse will increase the temperature to the point where carbon reactions can occur to produce heavier elements. Depending on the exact mass of the star, processes similar to those earlier ones in which an inert core is produced, which collapses and heats until new fusion reactions begind, can occur. The table shows some of the possible reactions: C + He --> O O + He --> Ne O + He --> Ne Ne + He --> Mg Mg + Ne --> Si C + H --> N O + H --> F Ne + H --> Na Mg + H --> Al Si + H --> P Whenever any of these fusion reaction occur in the core, energy is given off. Eventually, in the more massive stars, iron will be produced. Just as before, the inert iron core will begin to collapse. As the iron core collapses, temperatures increase, and the iron, which is not stable under these conditions, disintegrates--breaking up into neutrons and neutrinos (among other things). This disintegration produces more energy, which is used up in causing further disintegration of iron, etc. As this is going on, the core is collapsing. What occurs in an implosion of the star's core until the pressures become so large that the outer layers "bounce" off the core with tremendous energy. In addition, under the conditions present here (high temperature, high dencity), the neutrinos are able to interact with the matter. The combination of all this produces a tremendous explosion, called a supernova, in which most of the star blows up. They are so luminous that they can be seen in distant galaxies. Here's more! Results of a Supernova Explosion Increase in radiation: We observe a large increase in the amount of radiation produced. The details of how the radiation increases depend on the details of the explosion. neutrinos emitted: Scientists observed neutrinos to be emitted from the supernova called SN 1987a in the Large Magellanic Cloud, a nearby galaxy some 170,000ly away. These observations verified some theories of supernova formation and wiped out others. spectral changes: As you might expect, the spectrum of an exploding star is quite different from that of a stable star. Furthermore, the spectrum changes dramatically with time. Emission lines of numerous elements are seen. The line widths indicate that the material expands at speeds of tens of thousands of km/sec. Remnant cloud: Some years after a supernova explosion, the ejected gases can be seen as nebulae on a photograph. These are supernova remnants; the best known in the Crab Nebula (but there are others, too!). (Here's a movie on the Crab Nebula!) Photographs in different colors show how different elements are distributed in the supernova remnant; astronomers use this information to work backwards to understand the star's interior structure just prior to the explosion as a way of comparing observation and theory. Central remnant: material at center of the imploding object is compressed into neutrons--the material can remain behind after the explosion and form a neutron star. This star's mass can be between 1.5 to 2.5 solar masses, made up of degenerate neutrons, and has a diameter between 10-20 km. Therefore, neutron stars are very dense: 1012 lbs/in3. Neutron Stars Mass=1.5-2.5 solar masses Diameter=10-20 km Density=1012 lbs/in3 Escape Velocity=200,000 km/sec=2/3 speed of light Can such objects be observed? We related the story of how the British graduate student, Jocelyn Bell, discovered objects to be known as pulsars, which showed strong increases in brightness with extremely precise periods of about 1 second. The object could not be a rotating white dwarf because white dwarfs rotating that fast would fly apart. It was finally realized that these pulsars were rotating neutron stars. A pulsar with a period of 0.033 seconds was found at the center of the Crab Nebula. In other words, the object is rotating some 30 times per second! Pulsar periods are very precise, but not constant; the periods are generally observed to increase with time, which means that the rotation must be slowing down as the object looses it rotational energy. For a 1-second pulsar, the period changes by some 10-15 seconds per rotation. it will change by 1 second in about 10 15 seconds, which is about 30 million years. generally, longer period pulsars are older than short period ones. We can determine the size of these objects by looking at the width of the pulse of radiation produced. The pulse width is very narrow. The object's size cannot be much larger than the time it takes light to travel across the object. Since the time it takes to change brightness is very small, we know that the object itself must be very small too. Emitted energy from pulsars If you look at a pulsar spectrum in the radio region of the spectrum, you find that the brightness increases with increasing wavelength. This is odd, because we've seen all semester that the brightness of a blackbody decreases with increasing wavelength. The pulsar observations, along with the fact that the radiation is highly polarized, tell us that the pulsar's radiation is not caused by a black body but by something called synchrotron radiation, or non-thermal radiation. The term non-thermal is used to indicate that the mechanism has nothing to do with temperature, which is the determining factor for thermal (blackbody) radiation. Synchrotron radiation caused when three things are all true: you have charged paricles, moving near the speed of light, in a magnetic field. The pulsar environment has all of these and the observed synchrotron is the result. Pulsar Model All these observations, together, provide us with a model of a pulsar as a rotating neutron star with a strong magnetic field. Particles from the supernova explosion are trapped in the magnetic field that accelerates them it to velocities near that of light. We see "pulses" of radiation because the axis of rotation, and the magnetic axes, are tilted to each other. as the pulsar rotates a beam of radiation will strike the observer each rotation, similar to a rotating light house beacon. Miscellaneous pulsar observations Pulsars located in binary systems have been found. From an analysis of the binary motion, the masses can be determined. These observed masses agree with the expected mass of a neutron star. Planets have been discovered around pulsars! It is not clear, however, how they formed/where they came from. Some pulsars have been observed having extremely short periods, such as 0.003 seconds. These are the millisecond pulsars. These rotate rapidly because, it is thought, material falling onto the neutron star spins it up, just like a ball rotating on your fingertip will speed up if you periodically strike it in the appropriate manner. Evolution of Highly Massive Stars A supernova will also occur at the time of death of a highly massive star. If the core remnant is more massive than 3 solar masses, it will not end up with a neutron star. If the mass increases, the degenerate pressure does not increase enough to hold the star up. Gravitational attraction will increase as the star continues to collapse. In particular, the force of gravity on the object's surface become very strong. What happens? The behavior of light in a strong gravititational field was studied by Einstein in his Theory of General Relativity. One of the prediction of this theory is that light will bend as it passes a massive object. The validation of this prediction occured at the total eclipse of the Sun in about 1917. What happens as a massive star collapses? Suppose you were ON the surface of a collapsing star and I was in orbit above you. You could signal could signal me with your flashlight. However, as the collapse occurs, there would be a time at which you could not signal me if I were your horizon because the light would not be able to escape from the object. As the collapse continue, the angle inside of which I must be for you to signal me would get smaller; this angle inside of which you can communicate with me is called the exit cone. Eventually, the size of the exit cone goes to zero; the space through which photons can escape the object completely closes off. When the exit cone closes, we have reached the object's event horizon; we can no longer communicate. The object has become a black hole, an object from which nothing, not even light can escape. Light travelling near the object will be bent, and light travelling even closer to the object could be bent around the object and returned in the same direction from which it came! The structure of the black hole will be the following: A place at the center known as the singularity where the object has collapsed into an infinitely small point and has infinitely large density. An empty region of space will surround the singularity. Around this is the event horizon, the distance from the singularity where photons cannot be ejected. This is surrounded by a photon sphere, a sphere of light that surrounds the collapsing object. How to search for Black Holes Look for regions in space that are emitting gamma rays and x-rays. There is a problem, however, because other objects such as neutron stars also emit x-rays. In order to distinguish between them, we need to look at mass-->black holes will have a higher mass than neutron stars. If the mass is less than 2 1/2 solar masses, it is a neutron star. If it is greater than 2.5-3 solar masses, then it is a black hole. The object Cygnus X-1 has been observed in x-rays to have a period of 5.6 days. It is a binary star, which explains that its brightness changes regularly every 5.6 days, since the star is being eclipsed regularly by the other object in the binary system. Not only is this a binary system, but it also emits x-rays and radio waves. Since it is a binary star, we can determine the mass of the thing we can see and the thing we can't see. The mass of the unseen object has been determined to be around 8 solar masses. It has been concluded that one of the objects in the binary system is a black hole. Should we believe all this stuff about black holes? Einstein's theory of relativity has proved to be a good scientific theory. It makes predictions that can be tested and verified. Because so much of Einstein's theory has been validated, it is safe to say that the existence of black holes is believable, since it is a natural consequence of Einstein's theory. However, one has to be extremely careful in making definitive statements. Sometime as mistakes can be made, as shown here. Blackholes are also thought to exist in the cores of certain galaxies; here's one in a Hubble Space Telescope image of the galaxy NGC 4261 and the massive elliptical galaxy M87. This concludes the formal part of the course-the part you will be tested on. Since students often say, if only we could learn just for the sake of learning-without having tests. Well, now's the opportunity! For the next 2 lectures I'll present some background and some of the current ideas concerning cosmology. I'll show you the observations and models we have to work with so you will see the evidence we have showing why we say the universe began with a big bang. Sunlight Earth First quarter Third quarter New Moon Full Moon Waxing Crescent Waning Crescent Waxing Gibbous Waning Gibbous Figure 1 The different phases of the Moon is caused by its revolutions about the Earth (see Figure 1). Review what is meant by the terms new moon, full moon, first quarter, third quarter, waxing and waning crescent, and waxing and waning gibbous. Here are some other facts about the motion of our nearest neighbor. The Earth and the Moon rotate and revolve counterclockwise. The period of rotation and revolution for the Moon is the same, hence it presents the same face to us on Earth. The lunar "farside" has only been photographed and studied recently after space travel became a reality. The synodic month is 29.5 days. This is the time it takes the moon to go from one new Moon to the next. This is almost equal to one month. In fact, the word month comes from the word "moonth". So, in one week the moon goes through one-quarter of its cycle. The Sun illuminates half the sphere of the Moon at all times. However, when the Moon is in its new phase, it lies in the same part of the sky as the Sun, and the illuminated face is away from Earth, so we don't see it. Since the Moon is in the same part of the sky as the Sun, it will rise with the Sun. assume sunset occurs at 6p.m. and sunrise occurs at 6 a.m. Since the Sun has been drawn in the west, it is 6 p.m. The Moon has been placed in the east, making the angle of elongation 180E. Therefore theMoon phase is full. This means that a full Moon rises in the east as the Sun sets in the west. Time: 6 p.m. Moon Phase: Full Elongation: 180E 9. If sunset occurs at 6 p.m. moon rise occurs at . Assuming the Moon is up for 12 hours, moon set will occur at . E W Zenith Nadir E W Zenith Nadir 6 10. Using the steps shown above, use the circles below to show the position of the Moon at 6 p.m. for all its phases. Assumesunset occurs at 6 p.m. Use the elongation to decide where the Moon will lie. Remember elongations east mean the Moon is east (counterclockwise) of the Sun. Time: 6 p.m. Time: 6 p.m. Phase: Full Phase: New Elongation: 180 E Elongation: Moon rise: Moon rise: Moon set: Moon set: E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir E W Zenith Nadir 7 Phase: First Quarter Phase: Waxing gibbous Time: 6 p.m. Tim e: 6 p.m. Elongation: Elongation: Moon rise: Moon rise: Moon set: Moon set: Time: 6 p.m. Phase: Waning crescent Phase: Third quarter Time: 6 p.m. Elongation: Elongation: Moon rise: Moon rise: Moon set: Moon set: 11. Using the same techniques, fill in the following Time: Midnight Time: Noon Phase: Phase: Elongation: 90 degrees E Elongation: 45 degrees E Time: Time: Phase: New Phase: waning crescent Elongation: Elong ation: Phase Name 0.00 Full Moon 0.00-0.25 Waning Gibbous Moon 0.25 Last Quarter Moon 0.25-0.50 Waning Crescent Moon 0.50 New Moon 0.50-0.75 Waxing Crescent Moon 0.75 First Quarter Moon 0.75-1.00 Waxing Gibbous Moon 1.00 Full Moon (again) "Waxing" means growing and "waning" means shrinking. One appropriate definition of "gibbous" is "swollen on one side." The Earth's rotational period gives us one time scale, most apparent by the motion of the Sun through the sky, giving us night and day. At night, the stars also rise in the East and set in the West, just like the Sun, the Moon, and the planets. The Earth rotates once in about 23 hours 56 minutes, not 24 hours. This 23 hour 56 minute rotational period is equal to one sidereal day. Because the Earth is orbiting the Sun, the Sun's apparent position relative to the stars in the sky changes slightly from one day to the next. So, for the Sun to appear in the same point in the sky from one day to the next, the Earth must do an extra 4 minutes of rotation, making a solar day equal to 24 hours. The motion of the Earth around the Sun takes one year and results in the Sun's apparent motion through the fixed pattern of stars in the sky. On this time scale, we also see the motion of the other planets, wandering among the stars. As the Earth spins (with a rotational period of 23 hours and 56 minutes), it also wobbles like a top. This precession has a period of 26,000 years and results in changes in the position of the North Celestial Pole with respect to the stars. The Moon orbits the Earth in about 1 month. It, like the Sun, moves from West to East relative to the stars. The planets also move West to East relative to the stars, except for occasional periods of retrograde motion when their motion relative to the stars reverses direction and they move East to West. This motion is a result of us looking at the planets from a moving platform - the Earth - which is also orbiting the Sun. We revisited some of the terms and coordinates used to define positions on the celestial sphere. The ecliptic is the extension of the Earth's orbit to the celestial sphere. The celestial equator is the extension of the Earth's equator to the celestial sphere. Because the Earth's spin axis is not aligned with its orbit axis, the ecliptic and the celestial equator meet at an angle in the sky. This 23.5 degree angle is the Earth's obliquity and is what gives Earth its seasons. The meridian is the line on the celestial sphere passing through your zenith (the point directly overhead, from the southern horizon to the northern horizon. As the Moon orbits the Earth, its appearance changes due to changing illumination from the Sun. When the Moon is near the Sun, it appears as a crescent. As it passes the Sun on the East, it goes from being a new moon to a waxing crescent. One quarter of the way around the Earth, half of the Moon will be illuminated and this is called the first quarter. Halfway around the Earth, the Moon is opposite the Sun in the sky and is fully illuminated. This is called full moon. Another quarter of the way around the Earth, the Moon will approach the Sun in the sky from the West and will be at third quarter phase. As the fraction of the Moon's face that is illuminated gets larger (between new moon, through first quarter, to full moon) it is said to be waxing. After full moon, the moon is waning. Between new moon and first quarter the moon is a waxing crescent. Between first quarter and full moon, it is waxing gibbous. Between full moon and third quarter, it is called waning gibbous. Between third quarter and new moon, it is a waning crescent. Day/Night Caused by Earth’s rotation on its axis ("spin"). One Earth rotation takes 24 hours, therefore we have 24 hour days: roughly 12 hours of darkness when we are facing away from the sun and 12 hours of light when we are facing the sun directly. Earth spins counterclockwise, the sun appears to rise in the East and set in the West. Observing the Same Face of the Moon from Earth We always see the same face of the Moon when looking from Earth. On any given night/day, every place on the Earth sees the same face of the Moon. This occurs because the Moon spins on its axis once for every time it revolves around the Earth (28.5 days). Phases of the Moon Every 28 days we see a complete cycle of Moon phases: New moon, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent The Moon changes in appearance gradually each night. Phases are caused by the relative position of the Moon with respect to the Earth and Sun. The Moon’s relative position changes as it revolves around the Earth. Waxing means increasing in size. A waxing phase appears to be lit on the right side. Waning means decreasing in size. A waning phase appears to be lit on the left side. One half of the Moon is always facing the sun and therefore one half is always lit. Because the Moon’s position relative to the Earth is the same on any given day regardless of where one might be on Earth, the same phase of the Moon is visible from everywhere on Earth for any given night/day. Because the Moon revolves around the Earth in a counterclockwise direction, the Moon rises later each day (approximately 1 hour). The Moon rises in the east and sets in the west because the Earth rotates in a counterclockwise direction. The moon is in the sky for roughly 12 hours in a 24-hour period. Therefore, if the full moon rises at 6 PM, it will set at 6 AM. The full moon rises at sunset and the new moon rises at sunrise. Based on the position of the Moon in its orbit around the Earth, it is possible to determine the approximate rise time of each phase. Eclipses Solar eclipses: The sun is blocked (eclipsed) by the Moon, the Moon is between the Earth and Sun. In this position, the Moon is in a new phase. Totality lasts only a few minutes. The shadow that is cast on Earth covers a relatively small area, and so can be seen from only a few places on Earth. Can occur twice per (Earth) year - when the Moon, Earth, and Sun are aligned and in the same plane. Lunar eclipses: The Earth is between the Sun and the Moon and casts a shadow on the Moon, causing it to appear grey, black, or red. In this position, the Moon is in a full phase. Totality lasts a few hours. Lunar eclipses can be seen from any place on the Earth that is experiencing night at the time of eclipse. Can occur twice per (Earth) year - when the Moon, Earth, and Sun are in the same plane. Seasons Seasons are caused by the tilt of the Earth (23.5 °) and the Earth’s revolution around the Sun. Even though the Earth’s orbit around the Sun is slightly elliptical, the distance of the Earth from the Sun IS NOT the cause of the seasons. In fact, the Earth is closest to the Sun while the Northern Hemisphere is experiencing winter. In the Northern Hemisphere, the Sun appears lower in the sky during the winter is at its lowest noontime angular height on December 21, and higher in the sky during the summer is at its highest noontime angular height on June 21. In winter, the Sun appears to rise in the Southeast and set in the southwest, and the daylength is at its shortest. In summer, the Sun appears to rise in the northeast and set in the northwest, and the daylength is at its longest. In winter, the Sun’s rays are less direct. In summer, the Sun’s rays are more direct. Seasons are reversed in the Northern and Southern Hemispheres. The Sun is never directly overhead (at a 90° angular height) at any latitude further north than the Tropic of Cancer (23.5°N), or further South than the Tropic of Capricorn (23.5°S). Within the tropics (23.5°S-23.5°N) the sun is directly overhead two times each year. The Sun is a normal G2 star, one of more than 100 billion stars in our galaxy. diameter: 1,390,000 km. mass: 1.989e30 kg temperature: 5800 K (surface) 15,600,000 K (core) The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). It is often said that the Sun is an "ordinary" star. the Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less than half the mass of the Sun. The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol. The Sun is, at present, about 75% hydrogen and 25% helium by mass (92.1% hydrogen and 7.8% helium by number of atoms); everything else ("metals") amounts to only 0.1%. This changes slowly over time as the Sun converts hydrogen to helium in its core. The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body. Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water. The Sun's energy output (3.86e33 ergs/second or 386 billion billion megawatts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation. The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field. A small region known as the chromosphere lies above the photosphere. The highly rarefied region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during eclipses (left). Temperatures in the corona are over 1,000,000 K. The Sun's magnetic field is very strong (by terrestrial standards) and very complicated. Its magnetosphere (also known as the heliosphere) extends well beyond Pluto. In addition to heat and light, the Sun also emits a low density stream of charged particles (mostly electrons and protons) known as the solar wind which propagates throughout the solar system at about 450 km/sec. The solar wind and the much higher energy particles ejected by solar flares can have dramatic effects on the Earth ranging from power line surges to radio interference to the beautiful aurora borealis. Recent data from the spacecraft Ulysses show that during the minimum of the solar cycle the solar wind emanating from the polar regions flows at nearly double the rate, 750 kilometers per second, that it does at lower latitudes. The composition of the solar wind also appears to differ in the polar regions. During the solar maximum, however, the solar wind moves at an intermediate speed. Further study of the solar wind will be done by the recently launched Wind, ACE and SOHO spacecraft from the dynamically stable vantage point directly between the Earth and the Sun about 1.6 million km from Earth. The solar wind has large effects on the tails of comets and even has measurable effects on the trajectories of spacecraft. Spectacular loops and prominences are often visible on the Sun's limb (left). The Sun's output is not entirely constant. Nor is the amount of sunspot activity. There was a period of very low sunspot activity in the latter half of the 17th century called the Maunder Minimum. It coincides with an abnormally cold period in northern Europe sometimes known as the Little Ice Age. Since the formation of the solar system the Sun's output has increased by about 40%. The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards, will result in the total destruction of the Earth (and probably the creation of a planetary nebula). The Sun's satellites There are nine planets and a large number of smaller objects orbiting the Sun. (Exactly which bodies should be classified as planets and which as "smaller objects" has been the source of some controversy, but in the end it is really only a matter of definition.) Distance Radius Mass Planet (000 km) (km) (kg) Discoverer Date --------- --------- ------ ------- ---------- ----- Mercury 57,910 2439 3.30e23 Venus 108,200 6052 4.87e24 Earth 149,600 6378 5.98e24 Mars 227,940 3397 6.42e23 Jupiter 778,330 71492 1.90e27 Saturn 1,426,940 60268 5.69e26 Uranus 2,870,990 25559 8.69e25 Herschel 1781 Neptune 4,497,070 24764 1.02e26 Galle 1846 Pluto 5,913,520 1160 1.31e22 Tombaugh 1930 More detailed data and definitions of terms can be found on the data page. E W Zenith Nadir E W Zenith Nadir 8 Time: Time: 3 p.m. Phase: waxing gibbous Phase: third quarter Elongation: Elongation: 12. What would be the best time to see a waning crescent? 13. The last new moon occurred on . When will the next full moon occur? 14. Can you see a waxing crescent at midnight? Give reasons for your answer. 15. For how many hours is a full moon visible? Show your reasoning. 16. For how many hours is the waning gibbous Moon visible? A waning gibbous Moon is often visible around 9 a.m. In what part of the sky will the waning gibbous Moon crescent lie around 9 a.m.? Using the diagram for question #12, fill in the following table with the times of Moonrise, Moon crosses the meridian and the Moonset for the various lunar phases. Consider that the Sun rises at 6:00 AM, the Sun crosses the meridian at noon, and the Sun sets at 6:00 PM. Day Phase Moonrise Moon Meridian Moonset 1 New 6 AM Noon 6 PM 3 Waxing Crescent 9 AM 3 PM 9 PM 7 1 st Quarter Noon 6 PM Midnight 10 Waxing Gibbous 3 PM 9 PM 3 AM 14 Full 6 PM Midnight 6 AM 17 Waning Gibbous 9 PM 3 AM 9 AM 21 3 rd Quarter Midnight 6 AM Noon 24 Waning Crescent 3 AM 9 AM 3 PM the Cedar River Watershed. The watershed supplies 70 percent of King County's water. The 91,339 acres of land is normally closed to the public. this summer, you could see Chester Morse Lake, the 89-year-old Masonry Dam, and the pristine Cedar Falls in person. The Falls run into Canyon Creek, forming a brilliant blue pool of water. It's so pure, you could drink it. And you do. When you turn on the faucet, you're gonna be seeing that water coming out of the faucet North Bend, WA At Landsburg, 1/3 of the annual flow of the Cedar River is diverted into pipes for drinking water. Over 100 million gallons of water a day are screened, chlorinated and fluoridated, then delivered to customers throughout the greater Seattle area. Canyon Creek Falls WA Granite Falls 7 1/2" On Canyon Creek, about 1 mile north of Granite Falls (falls, not town). Area around falls surrounded with private homes...or shacks. Only way to falls may be from personal watercraft (Kayak or Raft). Flight Computer On/Off SPST Switch on left hand side and Push button Arm/Safe SPDT Switch on right hand side. Hi I live in Kirkland near Seattle. Would you be interested in living in a long term relationship with me? I can give my care and love to you. Would you be interested in meeting me sometime? What do you like? from, Robert robrain@blarg.net Hi Would you like to meet me in person, and we can do somethings together. Like we could get to know each other while you cuddle up with me. Let me know if you want my street address for where I live I can give you my address if you want to meet me or I can meet you somewhere? from, Robert Greetings robrain, Thank you for registering at SinglesStopPersonals.com Here is you account info: username: robrain password: rob2 http://SinglesStopPersonals.com ------------------------- Best wishes SinglesStop.com staff http://SinglesStop.com Radiometric Dating How do we determine the age of a rock? 1.Relative dating - Steno's Laws, etc. "A is older than B" 2.Absolute dating Quantify the date in years. Radiometric Dating Principles of Radiometric Dating Naturally-occurring radioactive materials break down into other materials at known rates. This is known as radioactive decay. Radioactive parent elements decay to stable daughter elements. Radioactivity was discovered in 1896 by Henri Becquerel. In 1905, Rutherford and Boltwood used the principle of radioactive decay to measure the age of rocks and minerals (using Uranium decaying to produce Helium. In 1907, Boltwood dated a sample of urnanite based on uranium/lead ratios. Amazingly, this was all done before isotopes were known, and before the decay rates were known accurately. The invention of the MASS SPECTROMETER after World War I (post-1918) led to the discovery of more than 200 isotopes. Many radioactive elemtns can be used as geologic clocks. Each radioactive element decays at its own nearly constant rate. Once this rate is known, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements. Examples: Radioactive parent isotopes and their stable daughter products Radioactive Parent Stable Daughter Potassium 40 Argon 40 Rubidium 87 Strontium 87 Thorium 232 Lead 208 Uranium 235 Lead 207 Uranium 238 Lead 206 Carbon 14 Nitrogen 14 In the above table, note that the number is the mass number (the total number of protons plus neutrons). Note that the mass number may vary for an element, because of a differing number of neutrons. Elements with various numbers of neutrons are called isotopes of that element. Each radioactive isotope has its own unique half-life. A half-life is the time it takes for half of the parent radioactive element to decay to a daughter product. Examples: Half Lives for Radioactive Elements Radioactive Parent Stable Daughter Half life Potassium 40 Argon 40 1.25 billion yrs Rubidium 87 Strontium 87 48.8 billion yrs Thorium 232 Lead 208 14 billion years Uranium 235 Lead 207 704 million years Uranium 238 Lead 206 4.47 billion years Carbon 14 Nitrogen 14 5730 years Radioactive decay occurrs at a constant exponential or geometric rate. The rate of decay is proportional to the number of parent atoms present. The proportion of parent to daughter tells us the number of half-lives, which we can use to find the age in years. For example, if there are equal amounts of parent and daughter, then one half-life has passed. If there is three times as much daughter as parent, then two half-lives have passed. (see graph, above) Radioactive decay occurs by releasing particles and energy. Uranium decays producing subatomic particles, energy, and lead. As uranium-238 decays to lead, there are 13 intermediate radioactive daughter products formed (including radon, polonium, and other isotopes of uranium), and 8 alpha particles and 6 beta particles released. There are three types of subatomic particles involved: 1.Alpha particles large, easily stopped by paper charge = +2 mass = 4 2.Beta particles penetrate hundreds of times farther than alpha particles, but easily stopped compared with neutrons and gamma rays. charge = -1 mass = negligible 3.neutrons highly penetrating no charge mass = 1 Gamma rays (high energy X-rays) are also produced. Highly penetrating electromagnetic radiation. Photons (light). No charge or mass. Can penetrate concrete. Lead shield can be used. Minerals you can date Most minerals which contain radioactive isotopes are in igneous rocks. The dates they give indicate the time the magma cooled. Potassium 40 is found in: potassium feldspar (orthoclase) muscovite amphibole glauconite (greensand; found in some sedimentary rocks; rare) Uranium may be found in: zircon urananite monazite apatite sphene Note that some elements have both radioactive and non-radioactive isotopes. Examples: carbon, potassium. As seen in the tables above, there are three isotopes of uranium. Of these, U-238 is by far the most abundant (99.2739%). Radioactive elements tend to become concentrated in the residual melt that forms during the crystallization of igneous rocks. More common in SIALIC rocks (granite, granite pegmatite) and continental crust. How does Carbon-14 dating work? 1.Cosmic rays from the sun strike Nitrogen 14 atoms in the atmosphere and cause them to turn into radioactive Carbon 14, which combines with oxygen to form radioactive carbon dioxide. 2.Living things are in equilibrium with the atmosphere, and the radioactive carbon dioxide is absorbed and used by plants. The radioactive carbon dioxide gets into the food chain and the carbon cycle. 3.All living things contain a constant ratio of Carbon 14 to Carbon 12. (1 in a trillion). 4.At death, Carbon 14 exchange ceases and any Carbon 14 in the tissues of the organism begins to decay to Nitrogen 14, and is not replenished by new C-14. 5.The change in the Carbon 14 to Carbon 12 ratio is the basis for dating. 6.The half-life is so short (5730 years) that this method can only be used on materials less than 70,000 years old. Archaeological dating uses this method.) Also useful for dating the Pleistocene Epoch (Ice Ages). 7.Assumes that the rate of Carbon 14 production (and hence the amount of cosmic rays striking the Earth) has been constant (through the past 70,000 years). Fission Track Dating Charged particles from radioactive decay pass through mineral's crystal lattice and leave trails of damage called FISSION TRACKS. These trails are due to the spontaneous fission of uranium. Procedure to study: Enlarge tracks by etching in acid (so that they may be visible with light microscope) See readily with electron microscope Count the etched tracks (or note track density in an area) Useful in dating: Micas (up to 50,000 tracks per cm squared) Tektites Natural and synthetic (manmade) glass Reheating "anneals" or heals the tracks. The number of tracks per unit area is a function of age and uranium concentration. U - Uranium Uranium oxide has been used since Roman times for yellow pigments in glass. The element was discovered in 1789 by a German chemist, Martin Klaproth, who named it for the newly observed seventh planet. In 1841, French chemist Eugene Peligot extracted pure uranium metal, which caused little interest until March 1, 1869, when French physicist, Henry Becquerel serendipidously discovered radioactivity in uranium salts - suddenly uranium was hot stuff! Although only mildly radioactive, uranium compounds are toxic. U.gif NEAR-EARTH OBJECTS AND LIFE ON EARTH Although the exact process by which life formed on Earth is not well understood, the origin of life requires the presence of carbon-based molecules, liquid water and an energy source. Because some Near-Earth Objects contain carbon-based molecules and water ice, collisions of these object with Earth have significant agents of biologic as well as geologic change. For the first billion years of Earth's existence, the formation of life was prevented by a fusillade of comet and asteroid impacts that rendered the Earth's surface too hot to allow the existence of sufficient quantities of water and carbon-based molecules. Life on Earth began at the end of this period called the late heavy bombardment, some 3.8 billion years ago. The earliest known fossils on Earth date from 3.5 billion years ago and there is evidence that biological activity took place even earlier - just at the end of the period of late heavy bombardment. So the window when life began was very short. As soon as life could have formed on our planet, it did. But if life formed so quickly on Earth and there was little in the way of water and carbon-based molecules on the Earth's surface, then how were these building blocks of life delivered to the Earth's surface so quickly? The answer may involve the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules. Once the early rain of comets and asteroids upon the Earth subsided somewhat, subsequent impacts may well have delivered the water and carbon-based molecules to the Earth's surface providing the building blocks of life itself. It seems possible that the origin of life on the Earth's surface could have been first prevented by an enormous flux of impacting comets and asteroids, then a much less intense rain of comets may have deposited the very materials that allowed life to form some 3.5 - 3.8 billion years ago. Comets have this peculiar duality whereby they first brought the building blocks of life to Earth some 3.8 billion years ago and subsequent cometary collisions may have wiped out many of the developing life forms, allowing only the most adaptable species to evolve further. It now seems likely that a comet or asteroid struck near the Yucatan peninsula in Mexico some 65 million years ago and caused a massive extinction of more than 75% of the Earth's living organisms, including the dinosaurs. At the time, the mammals were small burrowing creatures that seemed to survive the catastrophic impact without too much difficulty. Because many of their larger competitors were destroyed, these mammals flourished. Since we humans evolved from these primitive mammals, we may owe our current preeminence atop Earth's food chain to collisions of comets and asteroids with the Earth. What's killing the fish in Lake Washington? 06/18/2003 By GARY CHITTIM / KING 5 News SEATTLE Residents and county agents say they often find large amounts of dead fish this time of year and figure it’s a natural die-off. But some scientists aren’t so sure. It started happening late last week and while county officials are investigating, officials did not comment to KING 5 News yet. At this point they don't seem sure why it's happening. You have to get close to the water to see the sunken graveyard of hundreds of Lake Washington fish, their shiny bodies stacked up on the bottom. But you don't have to get close at all to know they are washing up on the shore. Carcasses of the dead fish are strewn all over the beach. It’s not just little perch, but also big fish such as carp. Even the birds cannot keep up with the mess. County water experts and others say this is probably a natural event - low oxygen levels in the water due to high temperatures for several days. But they are finding that oxygen levels are not all that low and it usually only affects small fish like perch. So, what's this all about? Captured in pictures from KING 5s helicopter SkyKing were dozens of large, dead fish, apparently carp, in the middle of some discolored water on the north end of the lake, with even bigger live fish swimming nearby. The area's famous birds - eagles and herons - watch and wait for their turn to move in. Fish and wildlife agents are checking out the situation. At this point some suspect it may be more than the typical seasonal die-off, but could be caused by oxygen-robbing materials like yard fertilizer. More tests are needed and park users will have to get used to stepping over decaying carcasses. Juanita Beach Search KING5.com The Betty Mills Company 60 East 3rd Avenue Ste 201 San Mateo, CA 94401 Quantity Item # Product Price Total 1 UFS 56776 Royal Dansk Cookies $6.05 1 WEV CO284 #10 Self-Seal White Envelopes $8.69 1 PGC 40725 Bounty® Perforated Paper Towel Rolls $44.87 Subtotal: $6.05 Flat $12.95 delivery charge for all UPS shippable orders Shipping: $12.95 Grand Total: $72.56 What is kettle cooked? Our potato chips are hand-cooked batch by batch. (See potato facts for process) Where do you get your potatoes? We get our potatoes from Maine to Florida depending on the time of year. What kind of oil do you use? We use cottonseed oil, corn oil, sunflower oil and canola oil. However our Whole Earth Collection is made only with canola oil. How long is the cooking process? The cooking process takes around ten minutes. Homemade Low Calorie Potato Chips#13526 1 large potato, scrubbed clean and sliced wafer thin 1/2 teaspoon olive oil I also cut the cooking time down 2 minutes on each side was perfect salt or seasoning 1. Pour oil in a plastic Ziploc baggie, along with whatever seasoning or spice preferred. 2. Put potato slices in bag. 3. Blow up the bag and quickly seal it shut. 4. Shake vigorously until all the slices are coated. 5. Arrange slices in a circle on a microwave-proof plate. 6. Microwave on high for 4 minutes. 7. Turn chips over and re-arrange them so they cook evenly. 8. Microwave again for 2 minutes. 9. Turn. 10. Watch them carefully and microwave again for about 2 minutes or until they start to brown. 11. They must brown a little in places or they will not crisp up. 12. Remove and let cool. 13. The chips crisp when cooling. began to turn brown during the first of the two 2-minute segments. THE ROTATION OF THE MOON As just mentioned, the Moon's rotation period is precisely equal to its period of revolution about Earth-27.3 days so-the Moon keeps the same side facing Earth at all times (see Figure 8.10). To an astronaut standing on the Moon's near-side surface, Earth would appear almost stationary in the sky (although its daily rotation would be clearly evident). This condition, in which the spin of one body is precisely equal to (or synchronized with) its revolution around another body, is known as a synchronous orbit. The fact that the Moon is in a synchronous orbit around Earth is no accident. It is an inevitable consequence of the gravitational interaction between those two bodies. Figure 8.10 The Moon is slightly elongated in shape, with its long axis perpetually pointing toward Earth. The elongation is highly exaggerated in this diagram. Just as the Moon raises tides on Earth, Earth also produces a tidal bulge in the Moon. Because Earth is so much more massive, the tidal force on the Moon is about 20 times greater than that on Earth, and the Moon's tidal bulge is correspondingly larger. In Chapter 7 we saw how lunar tidal forces are causing Earth's spin to slow and how, as a result, Earth will eventually rotate on its axis at the same rate as the Moon revolves around Earth. (Sec. 7.6) Earth's rotation will not become synchronous with the Earth-Moon orbital period for hundreds of billions of years. In the case of the Moon, however, the process has already gone to completion. The Moon's much larger tidal deformation caused it to evolve into a synchronous orbit long ago, and the Moon is said to have become tidally locked to Earth. Most of the moons in the solar system are similarly locked by the tidal fields of their parent planets. In fact, the size of the lunar bulge is too great to be produced by Earth's present-day tidal influence. The explanation seems to be that, long ago, the distance from Earth to the Moon may have been as little as two-thirds of its current value, or about 250,000 km. Earth's tidal force on the Moon would then have been more than three times greater than it is today and could have accounted for the Moon's elongated shape. The resulting distortion could have "set" when the Moon solidified, surviving to the present day, while at the same time accelerating the synchronization of the Moon's orbit. MEASUREMENT OF MERCURY'S SPIN In principle, the ability to discern surface features on Mercury should allow us to measure its rotation rate simply by watching the motion of a particular region around the planet. In the mid-nineteenth century, an Italian astronomer named Giovanni Schiaparelli did just that. He concluded that Mercury always keeps one side facing the Sun, much as our Moon perpetually presents only one face to Earth. The explanation suggested for this synchronous rotation was the same as for the Moon-the tidal bulge raised in Mercury by the Sun had modified the planet's rotation rate until the bulge always pointed directly at the Sun. Although the surface features could not be seen clearly, the combination of Schiaparelli's observations and a plausible physical explanation was enough to convince most astronomers, and the belief that Mercury rotates synchronously with its revolution about the Sun (that is, once every 88 Earth days) persisted for almost half a century. In 1965, astronomers making radar observations of Mercury from the Arecibo radio telescope in Puerto Rico (see Figure 5.21) discovered that this long-held view was in error. The technique they used is illustrated in Figure 8.11, which shows a radar signal reflecting from the surface of a hypothetical planet. Let's imagine, for the purpose of this discussion, that the pulse of outgoing radiation is of a single frequency. Figure 8.11 A radar beam reflected from a rotating planet yields information about both the planet's overall motion and its rotation rate. The returning pulse bounced off the planet is very much weaker than the outgoing signal. First, the signal as a whole may be redshifted or blueshifted as a consequence of the Doppler effect, depending on the overall radial velocity of the planet with respect to Earth. Let's assume for simplicity that this velocity is zero, so that, on average, the frequency of the reflected signal is the same as the outgoing beam. Second, if the planet is rotating, the radiation reflected from the side of the planet moving toward us returns at a slightly higher frequency than the radiation reflected from the receding side. (Think of the two hemispheres as being separate sources of radiation and moving at slightly different velocities, one toward us and one away.) The effect is very similar to the rotational line broadening discussed in Chapter 4 (see Figure 4.18), except that in this case the radiation we are measuring was not emitted by the planet but only reflected from its surface. What we see in the reflected signal is a spread of frequencies on either side of the original frequency. By measuring the extent of that spread, we can determine the planet's rotational speed. In this way, the Arecibo researchers found that the rotation period of Mercury is not 88 days, as had previously been believed, but 59 days, exactly two-thirds of the planet's orbital period. Because there are exactly three rotations for every two revolutions, we say that there is a 3:2 spin-orbit resonance in Mercury's motion. In this context, the term resonance just means that two characteristic times-here Mercury's day and year-are related to each other in a simple way. An even simpler example of a spin-orbit resonance is the Moon's orbit around Earth. In that case, the rotation is synchronous with the revolution, so the resonance is said to be 1:1. Figure 8.12 illustrates some implications of Mercury's curious rotation for a hypothetical inhabitant of the planet. Mercury's solar day-the time from noon to noon, say-is actually 2 Mercury years long! The Sun stays "up" in the black Mercury sky for almost 3 Earth months at a time, after which follows nearly 3 months of darkness. At any given point in its orbit, Mercury presents the same face to the Sun not every time it revolves, but every other time. Figure 8.12 Mercury's orbital and rotational motions combine to produce a day that is 2 years long. The arrow represents an observer standing on the surface of the planet. At day 0, it is noon for our observer, and the Sun is directly overhead. By the time Mercury has completed one full orbit around the Sun and moved from day 0 to day 88, it has rotated on its axis exactly 1.5 times, so that it is now midnight at the observer's location. After another complete orbit, it is noon once again. The eccentricity of Mercury's orbit is not shown in this simplified diagram. left over from the formation of the solar system about 4.6 billion years ago. Most of these fragments of ancient space rubble - sometimes referred to by scientists as minor planets - can be found orbiting the Sun in a belt between Mars and Jupiter. This region in our solar system, called the Asteroid Belt or Main Belt, probably contains millions of asteroids ranging widely in size from Ceres, which at 940 km in diameter is about one-quarter the diameter of our Moon, to bodies that are less than 1 km across. There are more than 20,000 numbered asteroids. As asteroids revolve around the Sun in elliptical orbits, giant Jupiter’s gravity and occasional close encounters with Mars or with another asteroid change the asteroids’ orbits, knocking them out of the Main Belt and hurling them into space across the orbits of the planets. For example, Mars’ moons Phobos and Deimos may be captured asteroids. Scientists believe that stray asteroids or fragments of asteroids have slammed into Earth in the past, playing a major role both in altering the geological history of our planet and in the evolution of life on it. The extinction of the dinosaurs 65 million years ago has been linked to a devastating impact near the Yucatan peninsula in Mexico. Asteroids were first observed with telescopes in the early 1800s, and in 1802, the astronomer William Herschel first used the word "asteroid," which means "starlike" in Greek, to describe these celestial bodies. Most of what we have learned about asteroids in the past 200 years has been derived from telescopic observations. Ground-based telescopes are used to watch asteroids that orbit close to Earth, not only to detect new ones or keep track of them, but also to watch for any asteroids that might collide with Earth in the future. Scientists define near-Earth asteroids (NEAs) as those whose orbits never take them farther than about 195 million kilometers from the Sun. In the last few decades, astronomers have used instruments called spectroscopes to determine the chemical and mineral composition of asteroids by analyzing the light reflected off their surfaces. Scientists also examine meteorites - the remains of comets or asteroids that can be found on Earth - for clues to the origin of these bodies. About three-quarters of asteroids are extremely dark and are similar to carbon-rich meteorites called carbonaceous chondrites (C-type). About one-sixth of asteroids are reddish, stony-iron bodies (S-type). In 1997, instruments on the Hubble Space Telescope mapped Vesta, one of the largest asteroids, and found an enormous crater formed a billion years ago. Interestingly, Vesta is an uncommon asteroid type, yet meteorites hav-ing the same composition have been found on Earth. Could these be rem-nants from the collision that created Vesta’s giant crater? NASA’s Galileo spacecraft was the first to observe an asteroid close-up, fly-ing by main-belt asteroids Gaspra and Ida in 1991 and 1993, respectively. Gaspra and Ida proved to be irregularly shaped objects, rather like potatoes, riddled with craters and fractures, 19 km long and 52 km long respectively. Galileo also discovered that Ida has its own moon, Dactyl, a tiny body in orbit around the asteroid that may be a fragment from past collisions. NASA’s Near-Earth Asteroid Rendezvous (NEAR) mission was the first dedicated scientific mission to an asteroid. The NEAR Shoemaker spacecraft caught up with asteroid Eros in February 2000 and orbited the small body for a year, studying its surface, orbit, mass, composition, and magnetic field. In February 2001, mission controllers guided the spacecraft to the first-ever landing on an asteroid. Kit Inquiry 3-1a In addition to the two sources of errors given in the text give at least three additinal sources of random errors in our activity. Scientists usually refer to measurement uncertainties as errors. Kit Inquiry 3-2b Compute the uncertainty of the five angle measurements that you just made and record the result in Table 2 on the answer sheet. While the nomogram is a convenient device for converting your measurement to an angle, there is some degree of uncertainty in using it. Kit Inquiry 3-2c If you can read the angle to 0.1 of the distance between tick marks on the nomogram how accurately can you read the angle scale at an angle of 5? 20? 50? Kit Inquiry 3-2d What is the uncertainty in the angle for measurements made at 40 and 80 cm assuming +0.5 cm in the reading? Kit Inquiry 3-2e What produces the larger source of uncertainty in your angle, the uncertainty of your reading or the conversion to the angle using the nomogram? In other words does the use of the nomogram itself add significantly to the uncertainty in the resulting angle? How about when you use the graph? Does use of the graphs in Kit Figure 3-1-4 add significantly to the uncertainty of the resulting angle? Kit Inquiry 3-2f Now that you have the graph, you can use it to predict observational results for other distances. For example, use your graph to predict the angular size of a 1-meter object measured from a distance of 10 meters. Hint: Locate the number 10 on the horizontal axis and draw a vertical line upward until it intersects the curve. Then draw a horizontal line from this point toward the left until it intersects the angular size axis. Kit Inquiry 3-2g If the sights on the cross-staff were closer together than they should be, would the measured angle be smaller or larger than the true value? Hint: Check the nomogram for converting meterstick readings to angle measurements. Kit Inquiry 3-2h If, instead of pressing the zero end of the meterstick against your you were to hold it farther away from you, would the measured angles be smaller or larger than the true value? Kit Inquiry 3-2i Would the changes listed below make the cross-staff more accurate? (a) Making the entire instrument larger larger sliding piece, longer stick, and soon. (b) Having finer divisions marked on the meterstick. (c) Marking a scale of angles directly on the meterstick, so that it is not necessary to read the graph. Kit Inquiry 3-2j Are the theoretical values you plotted within the error bars of your observational data on the graph? If not, which one(s) aren't? Explain why this can happen. Kit Activity 3-3 Constructing and Using an Astronomical Quadrant Make a quadrant and use it to measure altitudes. for measuring the altitudes of celestial objects. the altitude of the horizon is 0 zenith or point overhead is 90. percent uncertainty = estimated uncertainty X100. average measured value For example for an average measured altitude of 30 and an uncertainty of 1 the percent uncertainty would be 1/30 x 100= 0.033 x 100 or about 3%. Kit Inquiry 3-3a Does the percent error increase or decrease with larger measured angles? Kit Inquiry 3-3b How should you figure in the effect of your height? Kit Inquiry 3-3c Determine the height of the building. Kit Inquiry 3-3d What kind of error random or systematic would each of the following effects introduce? (a) The quadrant is poorly assembled as in Kit 3-3-4. (b) The weight swings back and forth. (c) You are unable to sight the object in exactly the same way each time. (d) The wind blows toward you and moves the weight slightly toward you. (e) Suggest three other possible sources of error. Kit Activity 4-1 Measuring the Northern Stars Using a sky map as a guide to find the principal constellations and stars in the northern part of the sky at any time of year. Determine your latitude from the altitude of the polestar. Use your quadrant and cross-staff or stellar protractor to measure the positions and apparent motions of stars in the sky, and interpret the measurements. Kit Inquiry 4-1a Why is it incorrect simply to mark this data point above 30 E on the horizontal scale? The star Polaris is at 30 10E Locating Polaris and a second star on the graph. In this example the second star is located at an altitude of 40 horizontal line and an angular distance of 30 from the pole arc of circle. The intersection of these two lines fixes the position of the star on the graph. 40 30 polaris 20 10 0 10E 20E Kit Inquiry 4-1b On the basis of your observations, which stars those to the east or those to the west have altitudes that increase? Decrease? Maintain constant altitudes? Kit Inquiry 4-1c On the basis of your observations, describe in your own words the apparent motions of the northern sky. Do the angular distances of stars you measured from Polaris increase, decrease, or remain the same? Kit Inquiry 4-1d On the basis of your observations of the position angles of the various stars, how many degrees does the position angle of a star change in an hour? According to your measurements how long will it take the stars to rotate a full 360? You have just determined the Earth's sidereal period! Kit Inquiry 4-1e On the basis of your observations in this activity what was the latitude of the place where you made your measurements? Kit Activity 4-2 Mapping the Sky Use a map of the sky to locate the principal constellations and stars for your time and season. Recognize bright stars and some major constellations. Big Dipper and Pegasus are constellations. In Winter you will see the Orion as a prominent constellation in January mid at 9pm. Kit Inquiry 4-2a According to your observations in which part of the sky are the stars increasing their altitude? In which part of the sky are stars decreasing their altitude? Kit Inquiry 4-2b Were there differences between your measurements of separations between stars in the sky and the same separation as measured on the map? What is the relationship between the separation and the amount of the difference? Altitude of stars #1 #2 Star low in east name of star Star east of meridian name of star Star medium in west name of star Angles of stars enter star names #1 to #2 Sketch a constellation and enter values you measured. Kit Activity 4-3 The Diurnal Motion of the Sun Observed with a Gnomon. Set up a gnomon and use it to measure the altitude and azimuth of the Sun at various times of day. straight stick or rod can be used to make a gnomon. which is a instrument that casts a shadow. 6 inches long. put a large piece of paper or cardboard under the gnomon and draw an approximate north - south line on it. length of stick and length of shadow Kit Inquiry 4-3a What was the greatest altitude of the Sun on the day you made your observations? Kit Inquiry 4-3b From your graph, at what time did the greatest altitude of the Sun occur? Subjectively estimate the uncertainty in your determination of this time. Kit Inquiry 4-3c It is possible that you may not have been able to make your observations very close to sunset. You can estimate the time of sunset by extending the line on your graph until it intersects the time axis. Then read off the time of sunset at that point. Estimate the error of this extrapolation. Compare this time either with an observation you make of the time of sunset or with the time published in your local newspaper. If the times diifer, suggest reasons for the difference. Kit Inquiry 4-3d On the basis of your observations what was the azimuth angle of the Sun at its greatest altitude? What would you expect its azimuth to be then? Explain why your observations do or do not agree with what you expected. The Sun at maximum altitude north of latitude 23.5. Kit Inquiry 4-3e Determine the azimuth of the Sun at sunset. Do this by extrapolating the azimuth graph to the moment of sunset determined earlier. The error of this estimate will be smaller the closer to sunset you were able to make observations. What is your estimate of the azimuth and its error? Record this on your graph. Kit Inquiry 4-3f Due west is azimuth 270. Anything greater than this is north of west anything less than this is south of west. Did the Sun set north or south of due west or did it set exactly in the west? Record your answer on the graph. Where did you expect it to set? Explain why. Does what you observed make sense for the time of the year you made your observation? Kit Inquiry 4-3g What other effects would cause a difference between noon on the clock and the time of maximum altitude of the Sun? Kit Inquiry 4-3h Suppose there were a country where everyone set their clocks to 6 p.m. at the moment of sunset. What problems might arise as a result? There is a country like this Saudi Arabia. Kit Activity 4-4 The Motion of the Sun with Respect to the Stars Describe the apparent motion of the Sun among the stars. choose a bright easily recognizable star in the eastern part of the sky and another in the western part of the sky. For example in the late summer and early fall September and October you might choose Deneb star in the Cygnus constellation. in the east. Arcturus in Bootes in the west. In the spring Regulus star in Leo for an eastern star and Aldebaran in Taurus in the west. Kit Inquiry 4-4a Does the star in the east get higher or lower as time progresses? By roughly how many degrees per month? What about the star in the west? Kit Inquiry 4-4b Since you made your observations at the same time of evening the Sun will be roughly in the same position relative to the horizon each time although not exactly, as will be found by those who do Kit Activity 4-5. Making this assumption in what direction does the Sun appear to move among the stars during the course of the year in an easterly or westerly direction? Star 1 Name Date #1 #2 #3 Ave. Error Kit Activity 4-5 Observing the Sunset Point Discuss how the location of the sunrise and sunset points changes along the horizon throughout the year. Discuss how the altitude of the midday Sun on the meridian changes throughout the year. Kit Inquiry 4-5a Has the Sun moved northward or southward along the horizon? Kit Inquiry 4-5b Compute the rate of motion of the Sun in degrees per day by evaluating the ratio. total change in the angle between the Sun and the reference point. total number of days between the first and last observation. Did the rate of motion change over the course of your observations? Kit Inquiry 4-5c From the results that you obtained, would you expect the midday Sun the Sun when on the meridian at the end of your observation period to be higher or lower in the sky than it was at the beginning? Explain your conclusion? Kit Activity 4-6 The Motion and Phases of the Moon Describe the position and motions of the Moon relative to the Sun and stars. Latitude is the angle north or south of the equator. Longitude is the angle east or west of the prime meridian. Kit Inquiry 4-6a What are the horizontal and vertical coordinates of Betelgeuse? Kit Inquiry 4-6b What can you say about the Moon's coordinates on the star chart if it where located 20 from Capella and also 20 from Aldebaran? Draw 20 circles around each star. Determining the location of the Moon in the sky. 180 150 120 to moon 90 60 30 to sun Kit Inquiry 4-6c On the basis of your observations in which direction does the Moon move relative to the stars from east to west or from west to east? Kit Inquiry 4-6d On the basis of your observations what would you conclude about the Moon's orbital path relative to the ecliptic plane? The vertical axis on your star chart is marked off in degrees on the map by using this scale you can determine the angle on the sky through which the Moon has moved. The rate of motion of the Moon is this number of degrees divided by the number of days between your observations. Kit Inquiry 4-6e Using only the measurements you graphed of the Moon's motion relative to the background stars, what is the rate of motion in degrees per day? Approximately how many days will it take the Moon to complete a 360 circuit of the sky with respect to the stars? This time interval is called the sidereal period. Explain your reasoning completely and clearly. Kit Inquiry 4-6f Compare your Moon drawings with the estimates you have made of the angle between the Sun and the Moon on each date, and explain clearly and completely on your answer sheet how the Moon's phases come about. Include a diagram of the relative positions of the Earth, Sun, and the Moon. when the Moon returns to the identical phase. Kit Inquiry 4-6g On the basis of only your observations, how many days is the Moon's synodic period? Explain your reasoning completely and clearly. Answers to Kit Inquiries: Kit Inquiry 4-6a: June 19 and -16 Kit Inquiry 4-6b It is at either June 11 +3 or June 19 +4 which gives a position to about 10 accuracy. An observation from a third star could help. Kit Activity 4-7 The Motions of the Planets Describe in your own words the motions of the planets you observed. Kit Inquiry 4-7a Did the planet you observed move east or west relative to the stellar background or did it change its direction of motion? Mars retrograde motion Kit Inquiry 4-7b If a planet moves from east to west it is said to be in retrograde motion. Did you observe retrograde motion for any of the planets you observed? If so, which ones? Venus Saturn Kit Inquiry 4-7c Roughly how many degrees per day did the planets you observed move, from your first observation to your last one? Kit Activity 5-1 The Diameter of Earth Determined with a Gnomon stick is 6 inches long and shadow is 3 inches long. Determine the diameter of Earth. Kit Inquiry 5-1a What was the length of your gnomon? What was the length of the shadow at its shortest? What was the maximum altitude of the Sun on the day you made your observations? Does that altitude make sense? Kit Inquiry 5-1b What is the north-south distance, in miles or kilometers between the two locations from which the data were obtained? Kit Inquiry 5-1c What is the altitude measured by the other group? Kit Inquiry 5-1d What is the difference of the measured altitudes between the two locations? Kit Inquiry 5-1e What fraction of a circle is this difference? Kit Inquiry 5-1f What is the computed circumference of the Earth? Kit Inquiry 5-1g What is the computed radius of the Earth? Kit Inquiry 5-1h What is the percentage difference between your computed value and the value given in your book? Kit Activity 8-1 Earthquakes Given a seismograph record showing P- and S-waves, and a graph showing the arrival times for the waves as a function of distance, determine the location of a seismic epicenter. An epicenter is the location on the Earth's surface above the place where an earthquake takes place. seismographs from three cities Sitka, Alaska Charlotte, North Carolina, and Honolulu, Hawaii. Kit Activity 3-1 Constructing and Using a Stellar Protractor Make a protractor and use it to measure angles. Measure the angular size of an object from several distances, and plot a graph of the results with error bars. The protractor is a simple instrument for the measurement of angles and sizes. The protractor is made from cardboard paper with a fastening brad, movable arm, and Angle readings. Fixed Arrow on top. Read the angle to the nearest 0.1 -0.2 degrees. Making Measurements Setup two marks on the wall, 1 meter apart.Stand 2 meters from the marks and measure the angle between them, reading the protractor to the nearest 0.1 -0.2. Record in the table on your answer sheet the measurement you have just made of the angle between the two marks on the wall. Kit Inquiry 3-1a. give some additional sources of random errors. Kit Inquiry 3-1b What was the uncertainty of the five measurements that you just made? 8 and 12 meters greater distances Kit Inquiry 3-1c. Now that you have the graph, you can use it to predict observational results for other distances. For example use your graph to predict the angular size of a 1-meter object measured from a distance of 10 meters. Hint: Locate the number 10 on the horizontal line from this point toward the left until it intersects the angular size axis. Kit Inquiry 3-1d If, instead of pressing the end of the protractor against you were to hold it farther away would the measured angles be smaller or larger than the true value? Kit Inquiry 3-1e. Would the changes listed below make the protractor more precise? Why? (a) Making the entire instrument larger. (b) Having finer divisions marked on the protractor. From your observations you found that angular size changes with distance. The angular size formula. Angular size (in degrees)= 57.3 true size distance The angular size formula makes it possible to compute the angular size of an object, given its true size and distance. Kit Inquiry 3-1f Are the theoretically expected values within the error bars of your observational data on the graph? If not, which ones aren't? Explain why this can happen. 3. Write your answers to the Kit Inquiries on a separate piece of paper. Kit Activity 3-2 Constructing and Using an Astronomical Cross Staff page 15 Make a cross-staff and use it to measure angles. Measure the angular size of an object from several distances, and plot a graph of the results with error bars. The cross-staff is a simple instrument for the measurement of angles and angular sizes. In using a cross-staff to map the sky, you will obtain accuracy roughly equivalent to that obtained by most of the world's astronomers up until the naked-eye work of Tycho Brahe 1546-1601. and the subsequent work of Galileo in 1609 when he first observed the sky with a simple telescope. from cardboard to make a cross-staff Staple the GRATING HOLDER to its indicated location on the big crosspiece before you do any folding. Stand 4 meters away to objects being observed. The wide sights are 4-inches wide on left and right side. stand 4 meters away from the wall and measure the angle between the marks this time using medium-width sights. Nomograph for Cross-Staff Reading Width of Sights Angle inches centimeters 35 90 wide 50 30 80 Medium 40 25 70 Narrow 30 Wide Sights are 42 cm apart made of cardboard 4 meters long 1 meter object. In this activity, you will use the cross-staff to measure the angular size of an object at various distances. Making Measurements Set up two marks on the wall, 1 meter apart. Stand 2 meters from the marks and measure the angle between them, reading the meterstick to the nearest millimeter and writing the measurement in the Table. convert the meterstick reading to an angle with the formula, the nomogram. try to read the angle to the nearest tenth of a degree. Kit Inquiry 8-1a At what times were the waves first detected at each location? Estimate the time to a tenth of a minute. 8.06 8:08 8:10 8:12 8:14 8:16 Kit Inquiry 8-1b What is the distance of the epicenter from each station? Latitude Longitude Sitka 57 N 135 W Charlotte 35 N 81 W Honolulu 21 N 158 W Kit Inquiry 8-1c What is the longitude and latitude of the epicenter? Kit Activity 8-2 The Lunar Surface Kit Inquiry 8-2a Compare the features marked 1grid location R-3 and 2 grid location V-3 on this photograph. Which is raised and which is depressed and from what direction is the sunlight coming? How did you come to your conclusion? R3 V3 are in the lower left hand corner and if East starts out on left side of paper than the sunlight was coming from South East. Kit Inquiry 8-2b Some obvious features in this photograph are (a) Domes moundlike raised features of low elevation. (b) Mountains elevated features with steep slopes. (c) Craters circular depressions rather regular in form. C Craters is the answer. Kit Inquiry 8-2c What evidence can you find in this figure that at some time in the past the material of the mare regions flowed across the landscape? Their is some valleys or long lines cracks open clearly visible. Kit Inquiry 8-2d What features on the photograph have clearly been formed after this material stopped flowing? Mountains, craters, valleys. D2 H6 mountains D6 G8 craters R8 R9 valleys W6 valleys Kit Inquiry 8-2e Find features in Kit Figure 8-2-2 that could be described as isolated peaks. Also, find an example of a crater that has been submerged beneath flowing mare material. L4 F6 U8 Y6 R5 Kit Inquiry 8-2f Find an example of a crater that is superimposed on another crater. How can such a superposition be interpreted? Kit Inquiry 8-2g What would you judge to be the oldest features in the region? They are Mountains and Craters. The youngest? valleys older features appear more eroded and less distinct. Kit Activity 10-1 The Rotation of Jupiter Angular distance = 57.3 x measured linear distance through which it moved 66 minutes measured radius at the latitude of the Red Spot. measuring the positions of the red spots. measured radius at the latitude of the Red Spot. Kit Inquiry 10-1a Through what angular distance did it move in the time interval? Kit Inquiry 10-1b Through what angle did it move per hour? Kit Inquiry 10-1c Given that in one complete rotation the Spot rotates through 360 what is the period of rotation? image 1 taken at 9:14 Image 2 taken at 10:20 Kit Activity 10-2 The Galilean Satellites and the Mass of Jupiter The Galilean satellites can be seen with a small telescope. Kit Inquiry 10-2a On the basis of your data what is the period of each of the satellites? 5.0 Kit Inquiry 10-2b Measure the maximum distance of each satellite in millimeters from the center of Jupiter. This maximum distance is the orbit's semi-major axis. Express this distance in units of Jupiter's radius by measuring its diameter in millimeters and dividing by two. Finally, express each satellite's maximum distance from the center in kilometers by using Jupiter's size as given in your textbook. Kit Inquiry 10-2c Compute the mass of Jupiter. Be careful to express your numbers in the proper units. Kit Activity 11-1 The Wave Nature of Light Diffraction and Interference Kit Inquiry 11-1a Describe the appearance of the source of light at different slit widths. You may find it best to draw a sketch. Kit Inquiry 11-1b Does the source spread out in a direction that is parallel to the length of the slit or perpendicular to it? Kit Inquiry 11-1c Does the source spread out more when the slit is wide or when it is narrow? Kit Inquiry 11-1d Since the lens of a telescope acts as an opening to diffract light, one would expect that the amount of blurring in star images would depend on the size of the lens, just as the amount of blurring you observed with your eye depended on the width of the slit. Which do you think would produce sharper less blurred images a telescope with a large-diameter lens or one with a small lens? Kit Activity 11-2 The Wave Nature of Light Polarized Light Describe how you can produce and detect polarized light. Describe how you know the sky is polarized. 2 pieces of polarized filter. made from plastic been heated and stretched so pencil like molecules are aligned with another. Kit Inquiry 11-2a Describe what you observed, and explain why the light is bright in one situation and dark in the other. Kit Inquiry 11-2b Describe what you observed while rotating the filter. Nature produces polarized light in various ways. Kit Inquiry 11-2c In your own words describe what you see. Is the light in some circumstances more strongly polarized than in others? Kit Activity 12-1 Lenses and Images focal length of a lens Use a lens to magnify an object. Flourescent lamp or light telescope piece with lens screen and cross-staff as screen holder. Kit Inquiry 12-1a What are the focal lengths of the two lenses in our kit? Kit Inquiry 12-1b What was the image size of the light source as produced by each lens on the viewing screen? What is the distance of each lens from the light source? Kit Inquiry 12-1c For each lens, divide the observed image size by the focal length. Divide the actual size of the object by the distance from the lens to the object. What relationship appears to hold between the two quotients? Kit Inquiry 12-1d Was the observed image erect or inverted? Was it reversed right-to- left? Kit Inquiry 12-1e What happens? is the image chopped in half? Kit Inquiry 12-1f Why or why not? Draw a lens formin an image and ask what would happen if half the lens were covered? A lens can be used as a magnifier. The shorter its focal length the more powerfully it magnifies. Kit Inquiry 12-1g Is the magnified image you observed real or virtual? Kit Inquiry 12-1h Does the magnified image appear closer to you or farther away than the actual object? Answers to Kit Inquiries Kit Inquiry 12-1b The lens with the longer focal length forms the larger image. Kit Inquiry 12-1c They are equal. Kit Inquiry 12-1g Virtual Kit Inquiry 12-1h See Kit Figure 12-1-3 Contrary to your intuition the larger virtual image appears to be farther away! Kit Activity 12-2 Making a Telescope Compute the light gathering power, resolving power, and magnification of a telescope. Kit Inquiry 12-2a Calculate the light-gathering power of your telescope. Kit Inquiry 12-2b How does the resolving power of the objective of your telescope compare with your eye's resolving power? Kit Inquiry 12-2c Compare the apparent angular diameter of an object with and without the telescope. About how many times does your telescope magnify? Kit Inquiry 12-2d Calculate the magnification of your telescope using the focal lengths of the lenses that you measured earlier. Compare this value of the magnification with that found in Kit Inquiry 12-2c by finding the percentage difference between them. Diameter of objective Light gather power Resolving power? What is the magnification? Magnification Percentage difference Kit Activity 13-1 Observing Light Sources Through a Diffraction Grating Describe the spectra of an incandescent bulb Kit Inquiry 13-1a As you observe the spectrum of the incandescent bulb, do you see any regions between violet and red where no light is visible? That is, are there any gaps in the band of light? blue, green, yellow. Kit Inquiry 13-1b Which of the following best describes the appearance of the spectrum of a street lamp? (a) The lamp is emitting energy uniformly at all visible wavelengths. (b) The lamp is emitting energy at most visible wavelengths, not at all visible wavelengths. (c) The lamp is emitting nearly all its energy at only a few discrete wavelengths. Answers to Kit Inquiries 13-1a No such regions should be visible. 13-1b. (c) Kit Activity 13-2 Measuring Light Sources with a Spectrometer Construct a simple spectrometer and calibrate it using the green line of mercury. Identify which of the three principal types of spectra is being observed from its appearance in the spectrometer. A spectrometer is a device to view and measure a spectrum using the eye to detect the radiation. Its operation depends on a diffraction grating or a prism dispersing a beam of radiation into its component wavelengths or colors. radiation coming through a slit falls on the grating and disperses through an angle. Constructing the Instrument Spectrometer To build your spectrometer you will need a meterstick or yardstick, the spectrum scale and its brace from the activity kit, the adjustable slit, and the sliding piece of the cross- staff. Kit Inquiry 13-2a If the slit were 1 millimeter wide, about how far apart in angstroms would the wavelength of two lines have to be for your spectrometer to resolve them? The virtual image of the lines would also be 1 millimeter wide. How many angstroms does 1 mm on the wavelength scale of your spectrometer correspond to? Kit Inquiry 13-2b Describe in words the spectrum of an incandescent bulb. Over what rangle of wavelengths are the following colors found: Violet? Blue? Green? Yellow? Orange? Red? Kit Inquiry 13-2c What wavelength did you obtain for the blue line of mercury? For the green line? For the yellow line? For the red line? If it was observable? Kit Inquiry 13-2d What were the uncertainties of each wavelength you determined? Are they consistent with the laboratory values of the wavelengths or do there appear to be additional systematic errors? The Mercury wavelengths are 4358A, 5461A, and 5790A. Kit Inquiry 13-2e Observe a fluorescent lamp. in a darken room. Can you see any evidence of a continuous spectrum? Can you see any evidence of discrete emission features? Measure their wavelengths and try to identify the gas in the tube using kit figure 13-2-2. Kit Inquiry 13-2f Try to find a pinkish street lamp to observe at night. Note the wavelengths of any features you can see in its spectrum. Can you find an example of what is called a dark line in this spectrum that is a wavelength where energy is being absorbed rather than emitted? At what wavelength was the dark line? The gas in this tube is sodium. Kit Inquiry 13-2g Can you find a red neon light to observe? Measure its wavelengths and compare them to your mercury vapor observations. Kit Inquiry 13-2h If you have any colored pieces of plastic it is instructive to observe an ordinary light bulb through them. Describe the effect that each has on the light passing through it by contrasting the appearance of the spectrum of the light bulb with and without the plastic in front of it. Kit Inquiry 13-2i What are the wavelengths of the dark lines you observe? Kit Inquiry 13-2j Which of these lines if any, are due to hydrogen in the solar atmosphere? Kit Inquiry 13-2k How might you determine which dark lines in the spectrum are due to the Sun and which are due to absorption by the Earth's atmosphere? Answers to Kit Inquiries 13-2a About 40 A. 13-2c The wavelengths are Blue - 4358 A green- 5461 A and yellow -5780A. 13-2f. The dark line is at 5890A. Note how its appearance differs from those places in the spectrum that just don't have any light emitted the spaces between the bright lines. Kit Activity 14-1 Classification of Stellar Spectra Kit Inquiry 14-1a Summarize in your own words the characteristic features of each different spectral type referring only to kit figure 14-1-1a and 14-1-1b. 14-1-1a standard stars of known spectral type He I 4026 05 wavelength line He II 4200 He I 4471 He II 4686 4000 5000 6000 7000 wavelength Relative flux 14-1-1b G9 Gband CaI 4226 M1 Ca I 4226 M5 Kit Inquiry 14-1b What is the contradiction if a stellar spectrum exhibits both molecular lines and helium lines? How might such a contradiction be resolved? calcium lines and iron lines is very cool temperatures. ionized helium lines, and ionized hydrogen lines. Kit Activity 15-1 Parallax Describe what is meant by parallax. Measure the parallax of a nearby object with your cross-staff and determine its distance. D=57.3 x distance AB parallactic shift in degrees 10 shift is 3 200 meters Kit Inquiry 15-1a What did you obtain for the distance of the nearby object? How does this compare with the distance you obtained by pacing it off measuring its distance on a map? Compute the percentage difference between your parallax determination and that you obtained through direct measurement. Kit Inquiry 15-1b Discuss the systematic and random errors in the two methods of determining the distance to the nearby objects. Which one do you think is more accurate and why? Kit Activity 19-1 The Crab Nebula Determine the scale of a photograph given the angular separation of two objects. The Crab Nebula is a remnant of a supernova explosion in year 1054. Kit Inquiry 19-1a Measuring to a tenth of a millimeter, how far has the gas clump you are considering moved between the times when the photographs were taken? 19-1-1a nebula observed in 1942. 19-1-1b nebula observed in 1976. half of the time Kit Inquiry 19-1b How many millimeters is the gas clump from the nebula's center? Kit Inquiry 19-1c Use the results from the previous inquiries to determine how many years it took the gas clump to get from the supernova explosion to its current location. Kit Inquiry 19-1d What assumption are you implicitly making? Some of the stars have appeared to move by looking the two photographs. Kit Inquiry 19-1e According to your data in what year did the explosion occur? 1054. Kit Inquiry 19-1f Compute the percentage error in your answer from the year 1054. Kit Inquiry 19-1g Carefully measure the number of millimeters between the mercury lines of wavelength 3650A and 4358A. Kit Inquiry 19-1h How many angstroms are there in each millimeter on the photograph of the spectrum? we measure the expansion speed. Kit Inquiry 19-1i Measure in millimeters the maximum separation between the two components of the 3727 A emission line. Kit Inquiry 19-1j What is the separation of the two components in angstroms? Kit Inquiry 19-1k Use the Doppler shift formula to find the velocity of expansion of the nebula. The result of your calculation will be the velocity of one side relative to the other side. To find the expansion rate relative to the supernova in the middle, you need to divide the result of your calculation by two. Kit Inquiry 19-1l Using this expansion velocity how far in kilometers has the gas clump you measured in Part I moved since the supernova exploded? Star pair Separation seconds of arc AB 351 AC 689 AD 500 BC 596 BD 576 CD 302 kit Inquiry 19-1m What is the scale of the photograph in seconds of arc per millimeter? Find it by averaging the scales determined from each of the measured separations. Kit Inquiry 19-1n What is the distance in mm of your gas clump from the center of the nebula? How many seconds of arc is this? Express your result in degrees. Kit Inquiry 19-1o Now that you know the angular distance through which the gas clump has moved as well as the linear distance it has traveled use the angular size formula to determine the distance to the Crab Nebula in kilometers and light years. Kit Inquiry 19-1p Use whatever methods you like to try to determine which star is the neutron star in the Crab Nebula. The photographs of the Crab Nebula wew supplied by Owen Gingerich and Sky Publishing Corporation. Kit Activity 21-1 Classification of Galaxies Kit Inquiry 21-1a Examine the spiral galaxies in Kit Figure 21-1-1. In what ways do they differ from each other? List examples of different types of spirals, identifying them by their X and Y coordinates. Regular spirals seen in a2 and b3 c2 Irregular spirals a3 a4 c1 c3 elliptical spirals a2 b3 b4 c3 c4 Kit Inquiry 21-1b Examine the HDF and find edge on examples of each of the different classes of spirals. a2 a3 b3 b4 Kit Inquiry 21-1c How do the nonspiral galaxies differ from each other? Kit Inquiry 21-1d In Kit Figure 21-1-1 count all the galaxies in the region enclosed by box. Keep track of spirals and nonspirals Kit Inquiry 21-1e How many galaxies of all types do you think might be visible in the entire image? How did you make your estimate? Kit Activity 21-2 The Variation of Galaxy Sizes Kit Inquiry 21-2a If we were to assume that all spirals had the same size and that all ellipticals had the same size, how much of an error in the distance to an individual galaxy might we make? Kit Inquiry 21-2b A photograph of a cluster of galaxies in Hercules is shown in Kit Figure 21-2-2. Both the Virgo and Hercules clusters are photographed at the same scale. It is apparent that the galaxy images in the Hercules cluster are much smaller than those in Virgo. How much smaller do the galaxies appear in Hercules than in Virgo? If the Virgo cluster is 40 million light-years away, how far away would the Hercules cluster be? What assumption is implicit in this comparison? in hercules a lot smaller than in virgo. x-coordinate y-coordinate size mm smallest ellipticals spirals large 1 mm 2mm Appendix Activities and Observations with a Small Telescope Kit Inquiry A-a Face south with the telescope or binoculars in hand. East is to your left. Viewed in the telescope, which way is east? Which way is south? Kit Inquiry A-b What is the field of view of the telescope in degrees? Kit Inquiry A-c If you used more than one method to measure the field of view of the telescope, how well did they agree? Angular size field of view = 57.3 X longest dimension of book. distance from book. 10-cm 4-inch telescope. Kit Activity A-1 Map of the Moon You will need to make observations at as many different phases of the Moon as possible. Inquiry A-1a Can more detail be seen on some parts of the Moon than on others? If so, which? Yes. Inquiry A-1b Can more detail be seen at some phases of the Moon than at others? Which ones? How can you explain this? Inquiry A-1c How many different kinds of features did you observe and map? Describe each of the different features you drew? Inquiry A-1d How do your drawings compare with Galileo's drawing? Compare your composite drawing of the Moon with a photograph of the Moon. How many of the named features on the Moon did you record? Which of the different types of features shown did you recognize? Inquiry A-1e If you used a 2-inch circle to draw the Moon then 1 inch = 1000 miles in your drawings. Estimate the sizes of some of the features you drew. If you did not start with a 2-inch circle, adjust your calculation appropriately. Kit Activity A-2 Telescopic Observations of the Sun Inquiry A-2a Compare the brightness of the central part of the Sun's disk with that of the edge or limb of the Sun. Which one is brighter? You should be able to discern that the edge of the Sun's disk is somewhat darker than the center, a phenomenon known as limb darkening. about the structure of the Sun's atmosphere. Inquiry A-2b This simple observation of the differences in brightness of different parts of the solar disk shows us that the temperature of the Sun's atmosphere varies with depth. From the evidence of limb darkening, does the temperature increase or decrease with increasing depth? it is hotter at the center of the sun and cooler temperatures at the edge of the Sun. Inquiry A-2c Can you see any sunspots on the surface of the Sun? Can you tell if the spots tend to be isolated or come in groups? Inquiry A-2d If you determined a rate of spin for the Sun, what did you obtain? Explain how you did the determination from your data. Kit Activity A-3 The Diameter of the Sun Measure the diameter of the Sun using the pinhole activity and explain how it works. A pinhole camera is a box having a small hole through which light passes to form an image. By using such a camera one could easily measure the diameter of the Sun paper with hole in it, a small mirror, and a cardboard box. Inquiry A-3a Does the square hole cast a square image and the round hole a round image, or does the shape of the hole seem to have no major effect on the shape of the image? Inquiry A-3b Which hole casts the larger image, the small one or the large one? How does the increase in the size of the image compare with the increase in the size of the hole? Inquiry A-3c Which image is brighter? To what do you attribute this? Inquiry A-3d Which image do you think would be easiest to measure an accurate diameter? Explain your reasoning. Now measure the diameter of the sharper of the two images. Then measure the distance from the pinhole to the screen. Diameter of Sun = diameter of Sun's image distance of Sun distance of screen from pinhole If the Sun is 150 million km from the Earth, you can use the above ratio to compute the diameter of the Sun. Inquiry A-3e What do you compute for the diameter of the Sun? What is the percentage difference between your observed value and the value in your textbook? 178page179 pages. Answers to Kit Appendix Inquiries A-a East is on the right in an astronomical inverting telescope and on the left in binoculars or a non-inverting telescope. A-1b You should be able to see more detail near quarter phase, as the Sun strikes the mountains on the Moon obliquely and casts readily visible shadows. A-1d The quality of your drawing will depend on the size telescope used. With a telescope of aperture greater than a couple of inches your drawing should be better than Galileo's. A-2a The center is brighter than the limb, and is hotter. A-2b. Increase, since one sees deeper into the Sun in the center. A-3a The shape of the hole should have no effect. A-3c. The largest hole casts the brightest image. Kit Figure 21-1-1 Shows a Portion of a Hubble Deep Field. Galaxies appear to be in millimeters apart from each other at short, and far away distances some examples are C1 square 2 galaxies are 2.7 mm apart from each other irregular galaxies. A4 square 2 round regular galaxies 2.5mm B3 square 2 1.3 mm 2 faintly seen galaxies seemed faraway irregular A3 2.5mm spiral arms galaxies I counted just over 20 galaxies that were visible in each of the square pictures. 12 square pictures 1 2 3 4 a b c letters on top Part Iv A spectrum of the Crab Nebula. from 3650A - 4047A is 3.7 mm. 4047a - 4358 A is 3 mm long. 4358 - crab nebula is to end of right side is 6.9 mm long. Wolff Laboratories, iNC. BLOOD AGAR http://www7.tamu-commerce.edu/physics/astronomy/hwch3.htm Chapter 4 2. Ratio of Max. 4. 32 years 6. 39.4 AU 8. The arrows are about the the sun Mercury - Mariner 10 Mass (10 24 kg) 0.3302 Equatorial radius (km) 2439.7 Escape velocity (km/s) 4.3 Number of natural satellites 0 1 Planetary ring system No Length of day (hrs) 4222.6 Mercury Observational Parameters Discoverer: Unknown Discovery Date: Prehistoric Distance from Earth Minimum (10 6 km) 77.3 Maximum (10 6 km) 221.9 Apparent diameter from Earth Maximum (seconds of arc) 13. Minimum (seconds of arc) 4.5 Mercury Atmosphere Surface pressure: ~10-15 bar (0.001 picobar) Average temperature: 440 K (167 C) (590-725 K, sunward side) Total mass of atmosphere: <~1000 kg Atmospheric composition: 42% Oxygen (O2), 29% Sodium (Na), 22% Hydrogen (H2), 6% Helium (He), 0.5% Potassium (K), possible trace amounts of Argon (Ar), Carbon Dioxide (CO2), Water (H2O), Nitrogen (N2), Xenon (Xe), Krypton (Kr), Neon (Ne) (The atmosphere of Mercury is essentially a vacuum. Venus - Magellan, Pioneer Venus, Galileo Mass (10 24 kg) 4.8685 Equatorial radius (km) 6051.8 Volumetric mean radius (km) 6051.8 Escape velocity (km/s) 10.36 Number of natural satellites 0 1 Planetary ring system No No Venus Observational Parameters Discoverer: Unknown Discovery Date: Prehistoric Distance from Earth Minimum (106 km) 38.2 Maximum (106 km) 261.0 Apparent diameter from Earth Maximum (seconds of arc) 66.0 Minimum (seconds of arc) 9.7 Maximum visual magnitude -4.6 Venus Atmosphere Surface pressure: 92 bars Surface density: ~65. kg/m3 Scale height: 15.9 km Total mass of atmosphere: ~4.8 x 1020 kg Average temperature: 737 K (464 C) Diurnal temperature range: ~0 Wind speeds: 0.3 to 1.0 m/s (surface) Mean molecular weight: 43.45 g/mole Atmospheric composition (near surface, by volume): Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2) Minor (ppm): Sulfur Dioxide (SO2) - 150; Argon (Ar) - 70; Water (H2O) - 20; Carbon Monoxide (CO) - 17; Helium (He) - 12; Neon (Ne) - Earth - Galileo Mass (10 24 kg) 5.9736 Volume (10 10 km3) 108.321 Equatorial radius (km) 6378.1 Escape velocity (km/s) 11.186 Number of natural satellites 1 Planetary ring system No Length of day (hrs) 24.0000 hours Terrestrial Atmosphere Surface pressure: 1014 mb Surface density: 1.217 kg/m3 Scale height: 8.5 km Total mass of atmosphere: 5.1 x 1018 kg Total mass of hydrosphere: 1.4 x 1021 kg Average temperature: 288 K (15 C) Diurnal temperature range: 283 K to 293 K (10 to 20 C) Wind speeds: 0 to 100 m/s Mean molecular weight: 28.97 g/mole Atmospheric composition (by volume, dry air): Major : 78.084% Nitrogen (N2), 20.946% Oxygen (O2), Minor (ppm): Argon (Ar) - 9340; Carbon Dioxide (CO2) - 350 Neon (Ne) - 18.18; Helium (He) - 5.24; CH4 - 1.7 Krypton (Kr) - 1.14; Hydrogen (H2) - 0.55 Water is highly variable, typically makes up about 1% Moon - Lunar Prospector, Clementine, Galileo, Apollo, Lunar Orbiter Mass (10 24 kg) 0.07349 Equatorial radius (km) 1738.1 Escape velocity (km/s) 2.38 Mean values at opposition from Earth from Earth (km) 384,467 Apparent diameter (seconds of arc) 1864.2 Apparent visual magnitude -12.74 Lunar Atmosphere Diurnal temperature range: >100 K to <400 K (roughly -250 F to +250 F) Total mass of atmosphere: ~25,000 kg Surface pressure (night): 3 x 10-15 bar (2 x 10-12 torr) Abundance at surface: 2 x 105 particles/cm3 Estimated Composition (particles per cubic cm): Helium 4 (4He) - 40,000 ; Neon 20 (20Ne) - 40,000 ; Hydrogen (H2) - 35,000 Argon 40 (40Ar) - 30,000 ; Neon 22 (22Ne) - 5,000 ; Argon 36 (36Ar) - 2,000 Methane - 1000 ; Ammonia - 1000 ; Carbon Dioxide (CO2) - 1000 Trace Oxygen (O+), Aluminum (Al+), Silicon (Si+) Possible Phosphorus (P+), Sodium (Na+), Magnesium (Mg+) Composition of the tenuous lunar atmosphere is poorly known and variable, these are estimates of the upper limits of the nighttime ambient atmosphere composition. Daytime levels were difficult to measure due to heating and outgassing of Apollo surface experiments. Other Galaxies We know quite a bit about other galaxies by using information about the Milky Way and applying it them as well as our own observations of other galaxies to figure out what is going on out there. And the reverse is also true - characteristics of other galaxies can be applied to the Milky Way. Remember, we have a hard time seeing various parts of our own galaxy so checking out other galaxies gives us an idea about what distant parts of our galaxy looks like or what is probably happening in those places. By using the Cepheid Period-Luminosity relation to determine the distance to the Andromeda Galaxy (one of our closer neighbors), he found that it was 900,000 light years away! This distance was much greater than anyone even suspected and this is one of the close ones! Actually, he was a bit off - it is about 2,250,000 light years away - our distance estimate methods are a little bit better now. Not only did Hubble figure out that those fuzzy spiral nebula (like Andromeda) were actually very distant, separate objects, he started a whole new field of astronomy, the search of objects that could reveal distances to remote galaxies. To find the distances to far away galaxies, it is necessary to use objects whose brightnesses we know fairly well (or some other property that is well defined) and also objects that are bright enough to be seen at a great distance. Objects that fit both these criteria are referred to as Standard Candles. That's just sort of a cute nickname for bright, well behaved objects. What sort of things are Standard Candles? Here are some examples of them - Cepheids - The best thing to use, very bright, fairly common, reliable RR Lyrae - Like Cepheids, but not as useful, since not as bright. Generally used only for nearby galaxies Supernova - Very bright, pretty useful, but can be tricky since there are 2 types of Supernova, and some can be rather abnormal. Planetary Nebula - these are pretty hot, and produce a lot of UV light, so can be seen distinctly from other things in the galaxy, pretty reliable. Nova - pretty good, but not all nova are alike, so not as reliable OB stars - by looking at the brightest stars, you can sometimes get good distances, but these are only in certain types of galaxies and are often in regions of star formation that have quite a bit of dust. H II Regions - not so great, since they can have different sizes Globular Clusters - if you can't see individual stars, use a whole cluster, but not too good, since clusters are not exactly alike - different sizes, brightnesses Brightness of the entire galaxy - assuming that all galaxies have the same brightness is not too good, since they come in a range of brightnesses - often just the brightest galaxy in a group is used. and other methods. So once an astronomer can determine how far away a fuzzy blob in the sky is using a Standard Candle, then they'll know if the fuzzy blob is in our galaxy (a few thousand parsecs away) or is a distant galaxy (millions or more parsecs away). Astronomers are able to get distances for galaxies within about 1 billion light-years fairly reliably, but there tends to be greater and greater uncertainties in the values for greater and greater distances. If you were to look up all of the distances to even nearby galaxies (like Andromeda, or the Large Magellanic Cloud), you'd see a range of values, not just one single value. For very distant galaxies (say more than 1 billion light years) the distances that we derive are much more imprecise, and can always be improved. This is one of the reasons that bigger and better telescopes are being built all of the time, to measure more distances and better distances. Since we need to know how far away things are so we can figure out what the Universe is like. Galaxy Characteristics Once it was determined that many of those fuzzy things were actually quite distant galaxies, astronomers had to classify them. Why? Well we are a sort of sad and lonely people, but really it is because we could learn more about them if we could group them together in a way that was scientifically meaningful. This is sort of like how we can group stars into bins like Main Sequence, Red Giant, and so forth. We know that objects in such groups share common characteristics, and we can use that information to learn more about galaxies that we don't see very well, or that are too distant to measure all of their characteristics with much certainty. Figure 1. The Hubble Tuning fork diagram showing the different forms that galaxies come in. The main groups are the ellipticals, the spirals and the barred spirals. A transitional form is the Lenticular type (labelled S0). Anything that can't be placed on the Tuning fork due to unusual structures is simply labelled as Irregular. So what do they look like? Do they all look the same? No of course not, that would be too easy. Most often we classify galaxies based upon their appearance, since that is the most easily observed feature. The basic classification scheme that is used is known as the Hubble Tuning Fork Diagram (Gosh I wonder what clever astronomer thought that up). Yes, good old Eddy Hubble set down the framework for the primary classification scheme. There are some other schemes used, and there have been slight alterations to the guidelines that Hubble used, but it is pretty much still the same thing used today. It should be noted that this scheme is based only on appearance - the shapes of galaxies. It doesn't account for how they got into those shapes nor the differences in sizes that exist. Not only do the galaxy shapes vary, but also the content of the galaxies varies - different types of galaxies can have quite different types of stars in them and different environments. This can result in galaxies having different colors, different things happening (or not happening) in them, different ages, different evolutions, and so on. Remember the different stellar populations Population I - young star, chemically like the Sun, their presence indicates that current star formation is going on Population II - old stars dominate, metal deficient compositions, no new or significant star formation occurring Remember, galaxies are very far away, so you generally can't see individual stars but you can see large groups of stars. So that is why we talk about populations, since the characteristics of groups of stars is what we are able to measure. Let's start checking out the different types of galaxies that are out there. Ellipticals Figure 2. Several different elliptical galaxies are shown. Copyright Association of Universities for Research in Astronomy Inc. (AURA), all rights reserved. As the name implies, these are elliptical in shape, though some are not very elliptical but look like circles. To distinguish the different shapes we use a numerical designation along the lines of E0, E1, E2. all the way up to E7. The "E" is for elliptical, while the number describes the degree of ovalness. The number is found by measuring the long (a) and the short (b) axis, and taking those values and putting them into the following formula - 10(a-b)/a Figure 3. The method used for defining the different elliptical galaxies is illustrated here. The longest axis length is compared to the shortest length and a number based upon this value is used to distinguish the range of elongation. In the first case both axis are the same length, so the type is an E0, while in second, the value of 4.7 is found using the formula, which becomes 5, making that elliptical an E5. Ellipticals tend to look rather yellowish or orangish. This indicates that they are made up of mainly Population II stars. Observations of them show that there is no new (or significant) star formation occurring. And since there is not much star formation occurring, this means that there must not be a lot of gas, and dust in them, since this is what stars are made from. This also gives us a clue concerning how they were made - but I'll get to that later. If you were to look at how the stars in an elliptical galaxies move, you'd tend to see rather random motions (sort of how globular clusters move around our galaxy). Figure 4. A group of galaxies with a large cD (Giant Elliptical) in the center of the group. Image from the Hubble Space Telescope. The biggest of the ellipticals are often just called Giant Elliptical and these are the largest of all galaxies. They get a special designation rather than the E designation, they are labelled as cD galaxies - don't ask me why they're called that, they just are. Since these tend to be very spherical in shape, I guess they don't need the "E" designation scheme - but there are other features that make them distinct. They can have masses of up to 10 trillion solar masses (1013 Msolar). Since they are so big, they tend to be found in the center of groups or clusters of galaxies. It is likely that these big brutes weren't always that big, but have gotten bigger over time by eating up little galaxies that get too close to them (what we called Galactic Cannibalism). And on the other end of the scale one finds Dwarf Elliptical. These are among the smallest of all galaxies, typically with masses around a few million solar masses (106 Msolar). Dwarf Elliptical can be best described as galaxy groupies, since they tend to hang around much larger galaxies. If you look at a picture of the Andromeda Galaxy, you'll see two little dwarf ellipticals around it - those two fuzzy blobs near it. Because of this wide range of masses, ellipticals are sort of hard to figure out. Sometimes it is hard to determine if you are looking at a nearby dwarf elliptical, or a distant larger elliptical. Spirals Figure 5. Several different spiral galaxies. Copyright Association of Universities for Research in Astronomy Inc. (AURA) Spirals show a much greater range of structure than ellipticals, so their classification is a bit more complex. First there is the letter "S" designating the galaxy as a spiral. Then there are the cases where there is a Bar going through the center of the galaxy. If so, you need to add a "B" to the designation. Then there is the other characteristic - how big is the bulge compared to the entire galaxy, and how tightly wound up are the arms. There is the tendency that when the bulge is large, the arms are wound up pretty tightly. And when the bulge is really small, the arms are really spread out. The letters a, b, c and d are used to categorize this characteristic. So the various designations for spirals are Sa, Sb, Sc, Sd, SBa, SBb, SBc and SBd. Some people are a bit indecisive about a galaxy being in a particular group, so sometimes a spiral can be designated as a Sab, or Sbc, since they're not sure which group it belongs in. Spiral arms are easy to identify since they have a spiral structure or flat disk shape (if seen edge on). And of course they have the spiral arms due to the star formation that is occurring there, but remember, there is material between the arms, it is just not so exciting or easy to see. The arms stand out so well because they have all of those hot, big stars to light them up, as well as the H II regions in the area. The masses of spirals are typically a few billions to a trillion solar masses. And there is the added complication that they aren't made of the same stellar populations. The populations of stars varies depending upon where you are looking - in the disk you find Population I stars and in the bulge and halo you find Population II. This is why in color pictures of some spirals you see the disk looking bluish while the bulge looks yellowish-orangish. Figure 6. Classic examples of Barred spirals. Association of Universities for Research in Astronomy Inc. (AURA) Barred Spirals share pretty much the same characteristics as spirals, except for that extended bulge. It is sort of like someone has taken the normally circular bulge shape and stretched it out. The arms then start up on the ends of the bar. Because of this added structure, the arms in barred spirals tend to be wound up a little bit more tightly than in regular spirals. It is now thought that the Milky Way is a barred spiral, perhaps it could be classified as a SBb or maybe even an SBc. Figure 7. A barred spiral, NGC 6744. It is possible that this is what our Milky Way galaxy looks like. Notice how the arms are not very distinct and poorly defined. It is also thought that the Milky Way galaxy has a bar similar to this one. Image © Anglo-Australian Observatory, Photograph by David Malin. Lenticular Galaxies S0, SB0 also known as Lenticular Galaxies are sort of a cross between a spiral and elliptical. They are best described as having a flying saucer shape, since they have a disk and a bulge like a spiral galaxy, but no spiral arms. And the bulge is often pretty big! Because they don't have any spiral structure, they don't have much star formation going on (remember that's why we have a spiral structure). The lack of star formation indicates a lack of gas and dust out of which to make stars. So galaxies have mainly Population II stars in them. If they have a bar, then the SB0 designation is used (make sure you don't get the letters out of order for this designation!) In general S0 galaxies are pretty rare. Figure 8. Lenticular (or S0) galaxies. These look like a cross between an ellipticals and a spiral. You might think of them as a type of spiral galaxy without any spiral structure. The one on the left has a dusty plane, but that is unusual for these galaxies. The one on the right is in the same orientation, but shows no dusty structure. Copyright Association of Universities for Research in Astronomy Inc. (AURA), all rights reserved. Irregulars As with any classification system, there has to be a bunch of objects that don't fit in. For galaxies, these are the Irregulars. Amongst the more famous irregular galaxies are the two neighboring galaxies to the Milky Way, the Large and Small Magellanic Clouds (LMC and SMC). They sort of have a bar-like structure, but there isn't anything else there - no spiral structure no defined bulge, nothing. Figure 9. Some typical irregular galaxies. The Large Magellanic Cloud is in the middle, and the Small Magellanic Cloud is on the right. It is thought that if there was structure, like arms, then those parts of the galaxy could have been striped off due to either collisions or other gravitational interactions with larger galaxies. Galaxies don't have to actually get too close for there to be tidal disruptions of the galaxy structure. As previously mentioned, it is possible for one large galaxy to strip off the gas and dust from a small nearby galaxy and to suck it up. The bigger galaxy is basically eating away the star forming material (gas and dust). This is known as Galactic Cannibalism, (and is best served with fava beans and a nice chianti). Because irregular galaxies tend to be associated with rather tumultuous events, they tend to have a lot of star formation going on in them, but this isn't true for all of them, since there can be a wide range of stellar population (I and II) in different irregulars. Uranian Atmosphere Surface Pressure: >>1000 bars Temperature at 1 bar: ~76 K (-197 C) Temperature at 0.1 bar: ~53 K (-220 C) Density at 1 bar: ~0.42 kg/m3 Wind speeds: 0-200 m/s Scale height: 27.7 km Mean molecular weight: 2.64 g/mole Atmospheric composition (by volume, uncertainty in parentheses) Major: Molecular hydrogen (H2) - 82.5% (3.3%); Helium (He) - 15.2% (3.3%) Methane (CH4) - ~2.3% Minor (ppm): Hydrogen Deuteride (HD) - ~148 Aerosols: Ammonia ice, water ice, ammonia hydrosulfide, methane ice(?) Neptunian Atmosphere Surface Pressure: >1000 bars Temperature at 1 bar: ~72 K (-201 C) Temperature at 0.1 bar: ~55 K (-218 C) Density at 1 bar: ~0.45 kg/m3 Wind speeds: 0-200 m/s Scale height: 19.1 - 20.3 km Mean molecular weight: 2.53 - 2.69 g/mole Atmospheric composition (by volume, uncertainty in parentheses) Major: Molecular hydrogen (H2) - 80.0% (3.2%); Helium (He) - 19.0% (3.2%); Methane (CH4) 1.5% (0.5%) Minor (ppm): Hydrogen Deuteride (HD) - ~192; Ethane (C2H6) - ~1.5 Aerosols: Ammonia ice, water ice, ammonia hydrosulfide, methane ice(?) Pluto - Pluto Express Pluto Fact Sheet Pluto/Earth Comparison Bulk parameters Pluto Earth Ratio (Pluto/Earth) Mass (1024 kg) 0.0125 5.9736 0.0021 Volume (1010 km3) 0.715 108.321 0.0066 Equatorial radius (km) 1195 6378.1 0.187 Polar radius (km) 1195 6356.8 0.180 Volumetric mean radius (km) 1195 6371.0 0.178 Ellipticity (Flattening) 0.0000 0.00335 0.0 Mean density (kg/m3) 1750 5515 0.317 Surface gravity (m/s2) 0.58 9.80 0.059 Surface acceleration (m/s2) 0.58 9.78 0.059 Escape velocity (km/s) 1.1 11.19 0.0983 GM (x 106 km3/s2) 0.00083 0.3986 0.0021 Bond albedo 0.4 - 0.6 0.306 1.3 - 2.0 Visual geometric albedo 0.5 - 0.7 0.367 1.4 - 1.9 Visual magnitude V(1,0) -1.0 -3.86 - Solar irradiance (W/m2) 0.89 1367.6 0.0007 Black-body temperature (K) ~37.5 254.3 0.147 Number of natural satellites 1 1 Planetary ring system No No Orbital parameters Pluto Earth Ratio (Pluto/Earth) Semimajor axis (106 km) 5869.66 149.60 39.236 Sidereal orbit period (days) 90,465 365.256 247.68 Tropical orbit period (days) 90,588 365.242 248.02 Perihelion (106 km) 4434.99 147.09 30.152 Aphelion (106 km) 7304.33 152.10 48.023 Synodic period (days) 366.73 - - Mean orbital velocity (km/s) 4.72 29.78 0.158 Max. orbital velocity (km/s) 6.10 30.29 0.201 Min. orbital velocity (km/s) 3.71 29.29 0.127 Orbit inclination (deg) 17.16 0.000 - Orbit eccentricity 0.2444 0.0167 14.635 Sidereal rotation period (hrs) -153.2928 23.9345 6.405 Length of day (hrs) 153.2820 24.0000 6.387 Obliquity to orbit (deg) 122.53 23.45 (2.451) Pluto Observational Parameters Discoverer: Clyde Tombaugh Discovery Date: 18 February 1930 Distance from Earth Minimum (106 km) 4293.7 Maximum (106 km) 7533.3 Apparent diameter from Earth Maximum (seconds of arc) 0.11 Minimum (seconds of arc) 0.06 Mean values at opposition from Earth Distance from Earth (106 km) 5750.54 Apparent diameter (seconds of arc) 0.08 Apparent visual magnitude 15.1 Maximum apparent visual magnitude 13.65 Pluto Mean Orbital Elements (J2000) Semimajor axis (AU) 39.48168677 Orbital eccentricity 0.24880766 Orbital inclination (deg) 17.14175 Longitude of ascending node (deg) 110.30347 Longitude of perihelion (deg) 224.06676 Mean longitude (deg) 238.92881 On 11 February 1999 at 11:22 UT (6:22 a.m. EST), Pluto passed Neptune as the furthest planet from the Sun once again and will remain so until 5 April 2231. North Pole of Rotation Right Ascension: 313.02 Declination : 9.09 Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0) Pluto Atmosphere Surface Pressure: ~3 microbar Average temperature: ~50 K (-223 C) Scale height: ~60 km Mean molecular weight: ~16-25 g/mole Atmospheric composition: Methane (CH4), Nitrogen (N2) Charon Mean distance from Pluto (km) 19,600 Sidereal orbit period (days) 6.38725 Sidereal rotation period (days) 6.38725 Orbital inclination to Pluto (deg) 0.0 Orbital eccentricity 0.0 Equatorial radius (km) 593 Mass (1021 kg) 1.9 Mean density (kg/m3) 2000 Surface gravity (m/s2) 0.21 Escape velocity (km/s) 0.58 Geometric albedo 0.38 Apparent visual magnitude 16.8 What would happen to us if the sun went out for an hour?

    (disclaimer: This Will Not Happen.)

    Aside from widespread panic and confusion, not much (see (**) below). Earth would cool as it does after sunset, and we would be kept warm by the heat retained in the atmosphere, oceans, and land as we are every night.

    (**): This is with the assumption that the Sun is simply "frozen" for an hour--say, a giant bushel is put over it. If you actually turned off all fusion in the Sun, it would collapse and then explode, and then we'd have other fish to fry. Don't get confused--the Sun doesn't have enough mass to become a supernova, this would be a different process, which won't happen because you can't turn off all fusion in the Sun. Though there is a small but finite probability that it stop right now on its own. But it won't. Very probably. Very. But it could.

    If the Sun failed to turn back on in an hour (going back to the bushel case now), we would have serious problems. Certainly within a week the temperature on Earth would have dropped below freezing. People on the coasts might survive longer than the rest, because of the heat the oceans would release; on the other hand I could imagine some intense weather along the coasts due to the temperature gradients. People with large energy reserves would also last longer. I suppose the place to be would be in the ocean, under the layer of insulating ice that would form, near a geothermal vent (not recommended if you breathe air)--I'm not sure how long life here could last. Biologists?

    Is the Sun expanding? Will it ever explode?

    I heard the Sun is expanding with the time, will it ever explode, if not how big could it get?

    It is true that the Sun is very slowly expanding and getting brighter right now. The reason for this is that as it is burning hydrogen to helium in the core the amount of hydrogen there gradually decreases. In order to keep the energy generation rate the same, the temperature and density in the core must rise. This has the effect that the energy can flow to the surface a little faster and it puffs up the outer layers (as well slightly brightening the Sun).

    When the Sun runs out of hydrogen in its core completely (which won't be for another 5 billion years or so) nuclear reactions will stop there, but they will continue in a shell around the core. The core will contract (since it is not generating energy) and as it contracts it will heat up. Eventually it will get hot enough to start burning helium into carbon (a different nuclear reaction). While the core is contracting the hydrogen burning around it heats will heat up the outer layers which will expand, and while they do that they will cool. The Sun will then become what is called a Red giant and it's radius will be large enough to envelop the Earth!

    Eventually the Sun will also run out of helium in it's core. When this happens the core will contract again, but it will never be able to get hot enough to start burning any other elements into anything else. There will still be nuclear reactions of helium and hydrogen in shells around the core though, and these will continue to heat up the outer layers and cause them to move outwards. The core will eventually turn into what we call a white dwarf star, which is an extremely small (roughly Earth sized) dense star. A white dwarf does not generate energy so it will just slowly cool star. A white dwarf does not generate energy so it will just slowly cool as it shines. The outer layers of the Sun will turn into what we call a "planetary nebula" (although it has nothing to do with planets) and gradually drift out into the interstellar medium. Planetary nebulae are some of the most beautiful objects you can see in the night sky. Shown below is the ring nebula, for some more pictures look here.

    The Ring Nebula taken with HST

    So the Sun will never explode (even though more massive stars can and do). The difference is that the Sun isn't massive enough to ignite anything past helium in its core. More massive stars continue nuclear burning until they start making iron. This creates an unstable core which will then explode in a supernova explosion. Narrow Mouth HDPE Bottle Code: 301705-0001 Price: $0.90 https://www.thesciencefair.com/ Narrow Mouth HDPE Bottle - Pack of 12" HREF="http://www.thesciencefair.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=301705-0001-12&Category_Code=pla-bot-nar">30ml (1 oz.) Narrow Mouth HDPE Bottle - Pack of 12
    Code:301705-0001-12 Price: $9.80 Plastic Safety Goggles Code: 315080 Price: $4.99 Latex Gloves - Lightly Powdered - Box of 100 Code: LGLP Price: $10.95 Nutrient Agar - 10 Prepared Plates Code: AA-82-1862 Price: $15.95 Potato Dextrose Agar - 10 Prepared Plates Code: AA-82-1902 Price: $16.95 Sterile Swabs - Pack of 2 Code: 2004-11 Price: $0.30 Agar Powder - 100g Code: SA-093-14M Price: $32.95 Petri Dish - Polystyrene, 25 per sleeve Code: SA00371-M Price: $7.99 Microscope Slides - Frosted Box of 72 Code: 1305-2 Price: $8.99 Cover Slips - 18mm x 18mm Box of 100 Code: 1305-20 Price: $2.99 Cover Slips - 22mm x 22mm Box of 100" HREF="http://www.thesciencefair.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=1305-21&Category_Code=mic-acc-sli">Cover Slips - 22mm x 22mm Box of 100
    Code:1305-21
    Price:$3.99 Microscope Slides - Single Cavity Box of 72 Code: 1305-3 Price: $26.25 Microscope Slides - Plain Pack of 12 Code: 1305-5 Price: $2.99 Petri Culture Dishes - Glass - 75mm Dia. Code: 1500-2 Price: $1.75 Petri Culture Dishes - Glass - 90mm Dia. Code: 1500-3 Price: $2.10 Petri Culture Dishes - Glass - 150mm Dia. Code: 1500-6 Price: $5.99 Petri Dish - Polystyrene, 25 per sleeve Code: SA00371-M Price: $7.99 safety precautions should be followed when growing bacteria, whether a known strain or unidentified species from environmental sources. Pure cultures of otherwise " harmless bacteria & can become contaminated with potential pathogens (disease causing!). Likewise, bacteria cultured from the skin, mouth, sinks or dirt can be potentially dangerous if they get into cuts or contact with mucous membranes, including the eyes, mouth, nose or ears. Always wear latex gloves and protective clothing such as a lab coat and safety goggles when handling your cultures and be certain to properly dispose of your experiments when finished. To grow bacteria you need to supply them with nutrients (a food source). In the particular case of blood agar the bacteria are getting the majority of their nutrients from the blood (could be sheep' blood), other nutrients which are necessary for growth may be added to the agar. The bacteria do not use the agar for growth, in fact the agar merely provides a semi-solid surface to grow the bacteria on. As for temperature, if you are growing bacteria on blood agar plates it usually implies that you are trying to culture bacteria which live in an animal. Therefore you would want to incubate the plates at the same body temperature of the animal. For example, take a sterile cotton swab and swab the inside of your cheek and then use this swab to streak a blood agar plate. Since our body temperature is usually 98.6’F (37 C) you would want to incubate the blood agar plate at 37 Celsius as the bacteria are accustomed to this temperature. Item Unit Price Quantity Subtotal Petri Dishes & Nutrient Agar $17.99 1 17.99 Total Purchases 17.99 Shipping 5.99 Tax 0.00 Total for Auspex Scientific $23.98 This kit contains 20 Clear Plastic Petri Dishes, and a bottle of Nutrient Agar Powder (~ 5 gm). It is very easy to prepare the agar culture medium. Just mix with water, bring to a boil, and pour into the dishes. The process takes only a few minutes, and you will have fresh culture medium to use. The sterile petri dishes are packaged in a plastic bag. There is more than enough Agar power for 21 dishes. Comes with short instruction on how to prepare the Agar culture medium. You can grow different types of bacteria you find around the house. Do experiments on them, to find out what conditions are condusive to the growth of the bacteria, and what brands of disinfectant and antiseptic are effective in killing them. Standard size of the dishes: 15mm x 100mm. For science projects or classroom use only. Use under qualified adult supervision. Petri Dishes & Nutrient Agar PDNA20Regular price: $18.99Sale price: $17.99 Nutrient Agar Powder Regular price: $9.99 Sale price: $8.99 Bacteriological Gram Stain Kit Regular price: $22.99 Sale price: $19.99 Gram Stain is one of the most widely used differential staining gechniques in bacteriology. This technique allows the differentiation of bacteria into the gram-positive and the gram-negative groups. The division of bacteria into these two main groups is of great value in the identification of many bacteria. This kit allows you to identify Gram-Positive and Gram-Negative cells. Included in this kit are 15 ml each of the Crystal Violet Solution, Gram's Iodine Solution, Safanine (counter-stain) solution, and 30ml of the Alcohol/Acetone Solution. Enough to do over 100 tests. Adult supervision recommended. For ages 10 and up. This kit contains 20 Clear Plastic Petri Dishes, and a bottle of Nutrient Agar Powder (~ 5 gm). It is very easy to prepare the agar culture medium. Just mix with water, bring to a boil, and pour into the dishes. The process takes only a few minutes, and you will have fresh culture medium to use. The sterile petri dishes are packaged in a plastic bag. There is more than enough Agar power for 21 dishes. Comes with short instruction on how to prepare the Agar culture medium. You can grow different types of bacteria you find around the house. Do experiments on them, to find out what conditions are condusive to the growth of the bacteria, and what brands of disinfectant and antiseptic are effective in killing them. Standard size of the dishes: 15mm x 100mm. For science projects or classroom use only. Use under qualified adult supervision. Petri Dishes & Nutrient Agar PDNA20Regular price: $18.99Sale price: $17.99 minimum shipping/handling charge of $5.99. TOTAL PURCHASE ----------- SHIPPING CHARGE 0 to 19.99 ---------------------------- 5.99 20 to 29.99 --------------------------- 6.99 30 to 39.99 --------------------------- 7.99 40 to 49.99 --------------------------- 8.49 50 to 74.99 --------------------------- 8.99 75 to 99.99 -------------------------- 9.49 100 to 119.99 ------------------------ 9.99 120 to 129.99 ------------------------ 12.99 Auspex Scientific 1416 Union Boulevard Allentown PA 18109 TOFURKY JURKY TIF008 Ginger Teriyaki Jurky 2oz. regularly $2.69 Order TIF002 Original Tofurky Jurky, 2 oz 2.69 OrderTIF003 Peppered Tofury Jurky 2 oz. 2.69 Order TIF006 12-pak Peppered Tofury Jurky $30.45 Order TIF009 12-pak Ginger Teriyaki Tofury Jurky $30.45 Order Vegetarian Broth Mixes Delicious as the base for vegan soups and stews and the perfect flavorings for textured soy protein and instant gluten. (Adds flavor with less sodium than flavored soy proteins.) Less than 450 mg. sodium per serving. No animal products--no preservatives. 8.8 oz makes 50 cups. BB15 "Beef" Style Broth 8.8 oz $5.99 Order *product info CB15 "Chicken" Style Broth 8.8 oz $5.99 Order *product info VB15 Vegetable Broth 8.8 oz $5.99 Order *product info Worthington Foods *Product Info Order WF203 Chili (Vegetarian chili with beans), 20 oz, $3.39 Order WF208 Country Stew (Stew with veggie meat) NV, 19 oz, $3.39 Order WF211 Prime Stakes (Salisbury steak style patties) NV, 13 oz, $3.89 Order WF216 Savory Slices (Thinly sliced mock beef) NV, 13 oz, $3.89 Order WF218 Vegetable Steaks (Large beef style steak strips), 20 oz, $4.29 Order WF223 Tuno (tuna substitute) 12 oz. $3.89 Order WF301 LowFat Vejalinks (10 lowfat veggie hot dogs) NV, 19 oz, $4.29, Order WF302 LowFat Chili (Vegetarian chili lower in fat), 20 oz, $3.39 Tofu Mixes Tofu Mixes K Order FAN270 Tofu Scrambler Mix (Make veggie scrambled eggs), 2.7 oz, $2.19 6 or more only $1.99 The Mail Order Catalog 413 Farm Road P.O. Box 180 Summertown, TN 38483 EDUCATIONAL / EXPERIMENTER'S ITEMS [ORDERFORM] [HOMEPAGE] E-mail: sales@lehmanscientific.com Call Lehman Scientific at: (800) 784-8680 See the Order Form for guarantees and terms Battery Holder, "D" Cell. Snap-fit aluminum holder has mounting holes on the bottom and brass Fahnstock clips on each end. Great for all kinds of low-voltage experiments and demonstrations. Price: $0.95 ea. Dropping Pipet, (Medicine Dropper, Eye Dropper). Straight tip, rubber bulb, made with neutral glass. Approximate capacity is 2mL, overall length is approx. 100mm. Bag of ten (10). New. Price: $2.00 Electrode Kit. For experimenting with voltaic cells, fruit/vegetable batteries and electrolysis. Each kit contains six (6) electrodes, one each: aluminum, carbon, copper, zinc, iron and lead. Each electrode is 25mm X 125mm. Price: $5.95 Glass Lens Demonstration Set. Optically true with ground glass edges. Contains 6 lenses, one each of: double convex, plano-convex, double concave, plano-concave, concavo-convex, and convexo-concave in a fitted wooden case. New, by American Scientific; demonstration quality, may have very small chips on edges. 50mm diameter lens set- Price $12.50, 38mm lens set- Price $9.95 Knife Switches, SPST, SPDT, DPST, DPDT. Hard to find low-voltage knife switches. Fully visible connections to demonstrate circuits and current flow. Plastic base with screw holes for bench or panel mounting. SPST- $1.40 ea, SPDT- $2.00 ea, DPST- $2.15 ea, DPDT- $2.75 ea Prepared Microscope Slides. We have available over 620 different sets of prepared microscope slides ranging from Algae to Vascular Bundles and everything in between such as Tissue Slides, Angiosperm, Virology and Bacteriology, Ovary Sets, Floral Morphology. Most of these sets consist of 25 slide sets packed in a slide box. Also available are special sets such as Capsella Embryology, Filicales, Cordaitales, Lepidodendriales, and Fossil Angiosperms. We always have only a few sets in stock, all are available on special order. Please fax or email for the full list of slide sets that we can supply. Prepared Microscope Slide- Single Slide with Case, Bacillus Anthracis (Anthrax). Order #LSPS-124-SGL Price: $3.50 Click here for the list Prepared Slides! Click here to see some samples of the Prepared Slides! Prisms, Equilateral. Clear optical glass prisms for experiments in dispersion and refraction of light. Two sizes available: 25mm face X 100mm long- Price: $6.00 25mm face X 150mm long- Price: $10.00 Slide Boxes for Standard Microscope Slides. Wooden case with individually numbered slots. New, by American Scientific. 25 slide capacity- $4.95, 50 slide capacity- $6.95 Test Tube Brush, pack of 10. Brush has nylon bristles and a fan-shaped end to clean the round bottoms of test tubes. Brush size: 18mm dia. X 90mm long. New. Price per pack: $7.95 Tuning Fork Set, Aluminum. Used to demonstrate the relationship between sound and vibration, energy transfer by resonance, and as a source of standard frequencies. Includes 8 tuning forks in a fitted wood case: (Please note: These frequencies do not correspond to the American musical scale) C/256 Hz, D/288 Hz, E/320 Hz, F/341.3 Hz, G/384 Hz, A/426.6 Hz, B/480 Hz, C/512 Hz. Price: $25.00 Wimshurst Machine. Generates static high-voltage electric charge. The two 250mm diameter high-resistance disks are rotated in opposite directions by a hand-crank. Brushes collect the induced charge and store the charge in Leyden jar type capacitors. Can easily generate arcs up to 2-1/2" long (about 75,000 Volts) between the ball-ended electrodes. Leyden jars can be taken out of the circuit for a rapid series of smaller arcs if desired. New, by American Scientific. This is a Lehman Scientific pick for a great demonstration item, compare this price! Price $145.00 post apple scientific Magnesium Hydroxide, Powder, Lab, 500g - Single Unit PAS-C-5030-0500-01-N $19.63 $19.63 Magnesium Nitrate, Crystal, ACS, 500g - Single Unit PAS-C-5040-0500-01-L $25.01 $25.01 Magnesium Oxide, Powder, Reagent, 500g - Single Unit PAS-C-5050-0500-01-N $40.69 Subtotal $85.33 Zip/Postal Code Shipping $7.56 Total $92.89 Wolff Laboratories, Inc. 9025 Penn Ave. So. Minneapolis, MN 55431 1-800-642-9085 Products and Pricing Orders of $100.00 or more earn a 2% discount 02/Blood Agar Plate-5% sheep blood $3.92 $0.98 03/Chocolate Agar Plate - Haemophilus $9.60 $2.40 04/Distribution Fluid $2.20 $0.55 05/Enrichment Broth Tube $3.80 $0.95 06/Eosin Methylene Blue Agar EMB $3.80 $0.95 07/Hektoen Enteric Agar Plate - Salmonella $5.00 $1.25 08/KLMB Agar $6.40 $1.60 09/MacConkey Agar Plate $4.20 $1.05 10/Mannitol Salt Agar - I.D. of Staph. aureus $4.40 $1.10 11/Mueller-Hinton Agar Plate $3.80 $0.95 12/Mueller-Hinton Plate 150x15 $7.80 $1.95 13/Mueller-Hinton Blood Agar $4.80 $1.20 14/Mueller-Hinton Blood Agar 150x15 $8.80 $2.20 15/Mycosel Medium-Fungus Media $5.20 $1.30 16/Sabouraud Agar - Fungus $5.20 $1.30 17/TKT/FC Agar Plate $6.80 $1.70 18/Transport Media $2.32 $0.58 19/TSI Slant $4.40 $1.10 Tri-Plates and Quad Plates ID/Product 4-Pack 4+ ea. 20/Basic Tri-Plate $6.80 $1.70 21/Gram-Negative Tri-Plate $6.80 $1.70 22/BAP Quad $4.40 $1.10 23/General Quad $7.60 $1.90 24/Gram-Negative Quad $7.40 $1.85 25/MacConkey Quad $4.60 $1.15 26/Mastitis Quad (BP) $7.40 $1.85 27/Mastitis Quad (KLMB) $7.80 $1.95 28/Standard Quad $7.40 $1.85 29/Staph Quad $7.80 $1.95 30/Urine Quad $7.80 $1.95 Kits ID/Product 31/Bac-T-Kit $5.50 ea. 32/Last Kit $2.85 ea. 33/Field Kit (Sterile swab & transport media) $1.00 ea. Supplies ID/Product 34/Coagulase Plasma $7.25 ea. 35/ID Staining Kit - gram stain $8.00 ea. 36/Inoculating Loop $8.25 ea. 37/Sterile Swabs 100/box $19.00 ea. Sensitivity Discs ID/Product Cartridge of 50 38/Click Here to see available discs $8.20 ea. MG Scientific 8500 107th Street Pleasant Prairie, WI 53158 customerservice@mgscientific.com Columbia CNA Agar w/5% Sheep Blood // EMB Agar, Modified, Holt-Harris and Teague - BBL Prepared Plated Media, I Plate® and Bi-Plate Dishes (100x15mm Style, Divided) GSA Information Cat No Qty Price Quantity UOM 21941 20 $50.70 PK Hi Andrea I am a white male 36 years old. I live in Kirkland near Seattle. I only been in Florida once. Have you ever wanted to come to Seattle, Washington? Would you like to meet me sometime? I am single. What are you looking for in a long term relationship? Are you looking for love? If you were living with me I can give my care and love to you. What do you like to do? from, Robert robrain@blarg.net Your Hair Colour:red Your Hair Style: long Your Height: 5.6 Name: andrea Profile ID:6137 Age: 20 Sex:f Location:florida , miami , United States andre8115@hotmail.com The Science Fair Inc. Code Product Quantity Price/Ea. Total AA-82-1902 Potato Dextrose Agar - 10 Prepared Plates 1 $16.95 Total: $16.95 In 1939, Leo Szilard and Enrico Fermi began working together at Columbia. It was a very good combination, actually. They came up with the idea of using carbon in the form of graphite to slow the neutrons-this was from Fermi's earlier work in Rome-and they put the uranium oxide in boxes as loose powder. They built a structure that I think was six by six or eight by eight feet wide and about 10 feet high, with a radium-beryllium source of neutrons in the base. They then measured the distribution of neutrons at different levels. Fermi worked out the theory for the process. If there is a multiplication of neutrons in the structure, then one sees the distribution by height falling off slowly. It's an exponential fall-off, and so these were called exponential piles. From these measurements and the theory worked out by Fermi, one can determine whether one can build a larger structure that will maintain a self-sustaining chain reaction. The first piles were somewhat discouraging. Impurities in the graphite and the uranium oxide "captured" the neutrons, poisoning the reaction. Szilard went to work on industry to get them to produce purer graphite and purer uranium oxide. He visited the plants, discussed the processes in detail, and got them to start making graphite without boron, which is disastrous for chain reactions. Getting purer goods Fermi and Szilard started getting purer graphite about January 1942. They also knew that they needed to make the uranium oxide denser; they couldn't leave it as loose powder. Wally Zinn designed dies to press the uranium into cylinders that could be inserted into the graphite. We were getting a multiplication constant ("k") close to one. A k value of more than one would have permitted a chain reaction in an infinite amount of material. The chain reaction (or plutonium project) was then under the direction of Arthur Holly Compton, a Nobel Prize-winning physicist at the University of Chicago. In early 1942, Compton consolidated the work at Chicago. By July, the piles we built in Chicago indicated that, with a great deal of material, it would be possible to build a chain-reacting structure relatively soon, so it was worthwhile to continue to get better quality graphite and uranium oxide. Earlier, Szilard got metallurgists and industrial laboratories to start trying to produce uranium metal, something that had never been produced before. Industry and industrial laboratories spent an enormous amount of effort helping us. We had to press uranium oxide into 22,000 pseudospheres about the size of baseballs, and we had to machine about 400 tons of graphite. The graphite came to the university with rough surfaces, and it had to be made very smooth and very precise. Although Fermi understood the physics of the pile and could teach it to the rest of us, Zinn had a complete grasp of the steps and processes needed to build a self-sustaining nuclear reaction. He was exceptional at devising straightforward, reliable, and efficient solutions to an enormous variety of physics and engineering problems. He arranged for the personnel and equipment needed to get the job done. With half a dozen young physicists, a millwright named Gus Knuth, and 30 kids hired from "Back of the Yards"-the stockyards district-Zinn got all the graphite machined and the oxide pressed for the reactor. The pressing and machining "factory" ran 24 hours a day, with many of us working double shifts. Meanwhile, Zinn and Herb Anderson shared the responsibility of supervising the measurement of neutron activity. We started building the final chain reactor on November 16. Learning the physics For about eight weeks in September, October, and November, Fermi gave a series of several-hour weekly lectures. They were beautiful lectures, explaining everything that we were going to do. Two of the lectures described the measurements that would ascertain when the pile would go critical. He showed that when approaching the critical point, the exponential rate of rise of neutron intensity would become slower and slower. When the pile was still subcritical, but approaching the critical point, the neutron intensity would level off at increasingly larger values; the intensity approaches infinity as the critical point is neared. Criticality would be reached by adding sufficient layers to the pile. After the pile reached critical size, it could be controlled by using rods with cadmium foil that soaked up neutrons, preventing neutron reactions. The steps Fermi followed on December 2 in taking the pile up to and then above criticality were based on the formulas given in these lectures. (His written report, classified until 10 years later, showed that our measurements of the exponential pile's properties differed from the chain-reacting pile's actual properties only by about three-tenths to four-tenths of a percent.) When the reactor got to be about the size of the earlier exponential piles, we started putting in safety rods and leaving them in. That is, we put strips of wood with cadmium metal foil on the top edge into pre-machined slots in the graphite. That was all you needed to stop the reactor from working. These safety rods were removed once every day, with proper precautions, to check the approach to the critical condition. We reached 52 layers on November 30, and Fermi's extrapolations showed that the pile would become critical at the 56th layer. Fermi decided to add a 57th layer, so that it would be one layer above critical. Herbert Anderson and his late-shift group added the 57th layer the night of December 1. Fermi was not there, but he had previously arranged with Anderson that the safety rods would not be pulled. Anderson adhered to the agreement, even though it was very tempting not to do so. Some safety precautions On the morning of December 2, we began by checking that the neutron intensity was the same as Herb Anderson had measured the night before. A special safety rod, "ZIP," was attached by a rope to a heavy weight. The safety rod, which was horizontal, would be pulled into the pile if the weight was released. The trigger was a solenoid that could be activated by an ion-chamber amplifier relay system; if the neutron intensity got above a certain level, the ZIP would automatically go in. The rope for yet another gravity-driven safety rod was attached to the railing of the balcony overlooking the pile. Norman Hilberry stood by with an axe, ready to slash the rope. Fermi planned to use the last cadmium rod in the pile as a control rod. It would be set by hand at various positions so that we could measure neutron intensity for these positions. After the checks on the instruments were completed, Fermi instructed George Weil to move the cadmium rod to a position that was about halfway out, well below the critical condition. The neutron intensity rose, the counters increased their clicking rate for a short while, and then the rate became steady, as it was supposed to. While it was rising, Fermi periodically read some numbers and did a quick calculation on his slide rule, checking the exponential rate of rise of the neutron intensity in the pile. After the intensity had leveled off, he told Weil to move the cadmium rod another six inches. The neutron intensity in the pile rose further and then leveled off. The pile was still subcritical. Fermi had been busy noting the values on the back of his slide rule and calculating the rate of rise. After it had stabilized, Fermi told Weil to move the rod out another six inches. Again the neutron intensity increased and leveled off. The pile was still subcritical. Pausing in mid-intensity Fermi had been busy with his slide rule and he seemed very pleased with his calculations. Every time the intensity leveled off, it was at the values he had anticipated for the position of the control rod. He had the rod moved out another six inches. After it had stabilized this time, the neutron intensity in the pile had reached an intensity that was too high for the range of some of the instruments, and we paused to make adjustments. After the instruments were reset, Fermi told Weil to move the rod another six inches. The pile was still subcritical, and the neutron intensity was increasing slowly, when suddenly there was a loud crash! The safety rod, the ZIP, had been automatically released. The ion chamber intensity-set at an arbitrary level- had been exceeded, setting off the relay. The crash scared us, but it was a good test of the safety system. It was then 12:15 a.m., and Fermi said, "I'm hungry. Let's go to lunch." The other rods were put into the pile and locked. Some of us went over to the university's Commons and, as usual when we were outside the classified area, we did not talk about what we had been doing. We returned at about 2 o'clock. Fermi's measurements that morning established the approximate position of the control rod at which the pile would become self-sustaining-the critical point. He also established how fast the intensity would rise if he moved the rod beyond that point. He established the critical point by two methods: extrapolating from the intensity measurements, and by estimating where the exponential rate of rise would become zero, indicating the critical condition. The rate of rise would become slower and slower approaching critical. After passing through the critical stage, it would get faster again. Both measurement methods gave the same result. After lunch, Fermi started again, not at the last point, but the one before, to check that nothing had changed. Except for the one hand-controlled rod, all the other rods were again removed. Fermi asked for the last hand-controlled rod to be set at one of the positions where it had been in the morning. He checked the intensity and the rate of rise and the functioning of the instruments. The values were the same as they had been during the morning when the control rod was at the same position. He then asked Weil to set the rod where it had been before lunch. The recorder chart showed the neutron intensities for settings of 11 feet, 10 feet, and 9 feet, 6 inches. The recording scale was changed several times to better determine the rate of rise. At nine-and-a-half feet, the rod was within inches of the critical position. Fermi measured the changes in the rate of rise, then asked that the safety rod, the ZIP, be put in to bring down the intensity. Then he told Weil, "This time, take the control rod out 12 inches." After the control rod was set, the ZIP rod was removed from the pile, and Fermi said to Arthur Holly Compton, who was standing at his side, "This is going to do it. Now it will become self-sustaining. The trace will climb and continue to climb; it will not level off." Success Fermi computed the rate of rise after a minute. After another three minutes, he computed it again. After three more minutes, he calculated the rate of rise again, and it was the same. The pile was functioning exactly as he had expected. At this point he broke into a big, cheerful smile. He put away his slide rule and announced, "The reaction is self-sustaining." Fermi let the activity of the pile increase and watched the pen on the recorder chart. It continued to rise as it should, and the intensity did not level off. At 3:53, Fermi told Zinn to put the ZIP in. The radiation and the neutron intensity and the counting rates all decreased almost instantaneously. That was it. Fermi had successfully brought a pile to a chain reacting state, controlled it, and shut it down. There were no gongs, no fireworks. On December 2, Fermi carried out a completely quantitative experiment. If some of the numbers hadn't agreed with what he had expected, Fermi would not have proceeded. He would have stopped, and then he would have discussed with us what alternatives we had for doing auxiliary experiments in an attempt to try to understand the discrepancies. This was Fermi's style. He checked things- if things didn't work as expected, you did additional experiments to find the source of discrepancy. I want to stress that it was a quantitative experiment, not a dramatic show. There were no surprises for most of us there, including Fermi. It is very lovely when experiments work smoothly. Giant asteroid could hit Earth in 2014 Tuesday, September 2, 2003 Posted: 7:29 AM EDT (1129 GMT) LONDON, England (Reuters) -- A giant asteroid is heading for Earth and could hit in 2014, U.S. astronomers have warned British space monitors. But for those fearing Armageddon, don't be alarmed -- the chances of a catastrophic collision are just one in 909,000. Asteroid "2003 QQ47" will be closely monitored over the next two months. Its potential strike date is March 21, 2014, but astronomers say that any risk of impact is likely to decrease as further data is gathered. On impact, it could have the effect of 20 million Hiroshima atomic bombs, a spokesman for the British government's Near Earth Object Information Centre told BBC radio. The Centre issued the warning about the asteroid after the giant rock was first observed in New Mexico by the Lincoln Near Earth Asteroid Research Program. The Near Earth Object will be observable from Earth for the next two months and astronomers will continue to track it over this period, said Dr Alan Fitzsimmons, one of the expert team advising the Centre. Asteroids such as 2003 QQ47 are chunks of rock left over from the formation of the solar system 4.5 billion years ago. Most are kept at a safe distance from the Earth in the asteroid belt between Mars and Jupiter. But the gravitational influence of giant planets such as Jupiter can nudge asteroids out of these safe orbits and send them plunging towards Earth. Space Station Assembly Russian Soyuz Prelaunch Countdown Timeline The Soyuz crew arrives at the launch site more than five hours before launch. While technicians and engineers prepare the vehicle systems and launch pad, the crew suits up and enters the Soyuz. Hatches are sealed and tested, and the onboard systems are activated. After the communications systems are verified and final vehicle checks are complete, the launch pad support structures are retracted. One minute before liftoff, the vehicle converts to onboard power and the last umbilicals are removed. The following times are approximate. All times are keyed to elapsed time to liftoff. T- 34 Hours Booster is prepared for fuel loading T- 6:00:00 Batteries are installed in booster T- 5:30:00 State commission gives go to take launch vehicle T- 5:15:00 Crew arrives at site 254 T- 5:00:00 Tanking begins T- 4:20:00 Spacesuit donning T- 4:00:00 Booster is loaded with liquid oxygen T- 3:40:00 Crew meets delegations T- 3:10:00 Reports to the State commission T- 3:05:00 Transfer to the launch pad T- 3:00:00 Vehicle first and second stage oxidizer fueling complete T- 2:35:00 Crew arrives at launch vehicle T- 2:30:00 Crew ingress through orbital module side hatch T- 2:00:00 Crew in re-entry vehicle T- 1:45:00 Re-entry vehicle hardware tested; suits are ventilated T- 1:30:00 Launch command monitoring and supply unit prepared Orbital compartment hatch tested for sealing T- 1:00:00 Launch vehicle control system prepared for use; gyro instruments activated T - :45:00 Launch pad service structure halves are lowered T- :40:00 Re-entry vehicle hardware testing complete; leak checks performed on suits T- :30:00 Emergency escape system armed; launch command supply unit activated T- :25:00 Service towers withdrawn T- :15:00 Suit leak tests complete; crew engages personal escape hardware auto mode T- :10:00 Launch gyro instruments uncaged; crew activates on-board recorders T- 7:00 All prelaunch operations are complete T- 6:15 Key to launch command given at the launch site Automatic program of final launch operations is activated T- 6:00 All launch complex and vehicle systems ready for launch T- 5:00 Onboard systems switched to onboard control Ground measurement system activated by RUN 1 command Commander's controls activated Crew switches to suit air by closing helmets Launch key inserted in launch bunker T- 3:15 Combustion chambers of side and central engine pods purged with nitrogen T- 2:30 Booster propellant tank pressurization starts Onboard measurement system activated by RUN 2 command Prelaunch pressurization of all tanks with nitrogen begins T- 2:15 Oxidizer and fuel drain and safety valves of launch vehicle are closed Ground filling of oxidizer and nitrogen to the launch vehicle is terminated T- 1:00 Vehicle on internal power Automatic sequencer on First umbilical tower separates from booster T- :40 Ground power supply umbilical to third stage is disconnected T- :20 Launch command given at the launch position Central and side pod engines are turned on T- :15 Second umbilical tower separates from booster T- :10 Engine turbopumps at flight speed T- :05 First stage engines at maximum thrust T- :00 Fueling tower separates Lift off Space Station Assembly Russian Soyuz Launch Preparation Throughout history, more than 1,500 launches have been made with Soyuz launchers to orbit satellites for telecommunications, Earth observation, weather and scientific missions, as well as for human flights. The basic Soyuz vehicle is considered a three-stage launcher in Russian terms and is composed of: A lower portion consisting of four boosters in the first stage and a central core in the second stage. A upper portion, consisting of the third stage, payload adapter and payload fairing. Liquid oxygen and kerosene are used as propellants in all three Soyuz stages. First Stage Boosters The four boosters of the first stage are assembled laterally around the second stage central core. The boosters are identical and cylindrical-conic in shape with the oxygen tank located in the cone-shaped portion and the kerosene tank in the cylindrical portion. An NPO Energomash RD 107 engine with four main chambers and two gimbaled vernier thrusters is used in each booster. The vernier thrusters provide three-axis flight control. Ignition of the first stage boosters and the second stage central core occur simultaneously on the ground. When the boosters have completed their powered flight during ascent, they are separated, and the core second stage continues to function. First stage booster separation occurs when the predefined velocity is reached, which is about 118 seconds after liftoff. Second Stage An NPO Energomash RD 108 engine powers the Soyuz second stage. This engine differs from those of the boosters by the presence of four vernier thrusters, which are necessary for three-axis flight control of the launcher after the first stage boosters have separated. An equipment bay located atop the second stage operates during the entire flight of the first and second stages. Third Stage The third stage is linked to the Soyuz second stage by a latticework structure. When the second stage's powered flight is complete, the third stage engine is ignited. Separation of the two stages occurs by the direct ignition forces of the third stage engine. A single-turbopump RD 0110 engine from KB KhA powers the Soyuz third stage. The third stage engine is fired for about 240 seconds, and cutoff occurs when the calculated velocity increment is reached. After cutoff and separation, the third stage performs an avoidance maneuver by opening a outgassing valve in the liquid oxygen tank. Launcher Telemetry Tracking and Flight Safety Systems Soyuz launcher tracking and telemetry is provided through systems in the second and third stages. These two stages have their own radar transponders for ground tracking. Individual telemetry transmitters are in each stage. Launcher health status is downlinked to ground stations along the flight path. Telemetry and tracking data are transmitted to the Russian Mission Control Center, where the incoming data flow is recorded. Partial realtime data processing and plotting are performed for flight following an initial performance assessment. All flight data is analyzed and documented within a few hours after launch. Baikonur Cosmodrome Launch Operations Soyuz missions use the Baikonur Cosmodrome's proven infrastructure, and launches are performed by trained personnel with extensive operational experience. Baikonur Cosmodrome is located in the Republic of Kazakhstan in Central Asia, between 45 degrees and 46 degrees North latitude and 63 degrees East longitude. Two launch pads are dedicated to Soyuz missions. Final Launch Preparations The assembled launch vehicle is moved to the launch pad on a horizontal railcar. Transfer to the launch zone occurs two days before launch, during which the vehicle is erected and a launch rehearsal is performed that includes activation of all electrical and mechanical equipment. On launch day, the vehicle is loaded with propellant and the final countdown sequence is started at three hours before the liftoff time. ASTRONOMY COURSE BOOKS BCC ASTRO 101 - 3000 X03 *Note: A 1 REQUIRED COSMOS:ASTRONOMY IN NEW MILLENNIUM Auth: PASACHOFF 0030052181 $83.15 $62.4 Thomson Learning - Order Fulfillment PO Box 6904 Florence, KY 41022-6904 77.36 52.16 4.95 4.95 139.42 Orders placed on-line will receive the following shipping rates: Continental US Normal orders: postage $4.95 3. The Cosmos: Astronomy in the New Millennium (with CD-ROM and InfoTrac), 2nd Edition Jay M. Pasachoff, Alex Filippenko PB © 2004 ISBN/ISSN 0-534-39549-X List Price: $85.95, Your Price: $77.36 4. Voyages to the Stars and Galaxies (with CD-ROM and InfoTrac), 3rd Edition Andrew Fraknoi, David Morrison, Sidney Wolfe PB © 2004 ISBN/ISSN 0-534-39566-X List Price: $57.95, Your Price: $52.16 5. Voyages to the Planets (with CD-ROM and InfoTrac), 3rd Edition Andrew Fraknoi, David Morrison, Sidney Wolfe PB © 2004 ISBN/ISSN 0-534-39567-8 List Price: $57.95, Your Price: $52.16 6. Voyages Through the Universe (with CD-ROM and InfoTrac), 3rd Edition Andrew Fraknoi, David Morrison, Sidney Wolfe PB © 2004 ISBN/ISSN 0-534-40905-9 List Price: $90.95, Your Price: $81.86 7. Foundations of Astronomy (with InfoTrac and CD-ROM), 7th Edition Michael A. Seeds CB © 2003 ISBN/ISSN 0-534-39204-0 List Price: $90.95, Your Price: $81.86 8. Stars and Galaxies (with InfoTrac and TheSky CD-ROM), 3rd Edition Michael A. Seeds PB © 2003 ISBN/ISSN 0-534-39447-7 List Price: $57.95, Your Price: $52.16 9. The Solar System (with InfoTrac and CD-ROM), 3rd Edition Michael A. Seeds PB © 2003 ISBN/ISSN 0-534-39449-3 List Price: $57.95, Your Price: $52.16 10. Astronomy: The Solar System and Beyond (with InfoTrac and TheSky CD-ROM), 3rd Edition Michael A. Seeds PB © 2003 ISBN/ISSN 0-534-39537-6 List Price: $88.95, Your Price: $80.06 What's killing the fish in Lake Washington? Residents and county agents say they often find large amounts of dead fish this time of year and figure it's a natural die-off. But some scientists aren't so sure. Full story... Spam Remedy (3.17MB) Description: The powerful, effective and intelligent anti-spam tool. It automatically cleans spam messages out of your mailbox before you receive or read them. Features: Automatically Blocking Spam Spam Remedy automatically checks your mail boxes and filters unwanted, dangerous, or offensive mail messages to save your time from manually detecting and organizing mail messages. Effectively Spam Detecting A complex Aritificial Intelligence algorithm has been used in Spam Remedy product to detecting legitimate mail messages and spam messages,the technique has more precision than other filter-based and keyword-based anti-spam technologies. Be Sure You Get Your Right Mail Messages Spam Remedy doesn't confirm a spam message by a single keyword in mail content. It examines the entire message - source, headers and mail content to confirm whether it is a spam message. Hilltop HT 031 II 1500 State School; Gatesville, TX 76598 (Coryell Co.) 254/865-8901 (031) Nancy Botkin Gatesville GV 024 II 1401 State School Road; Gatesville, TX 76599 (Coryell Co.)Linda Ament (GVWAR01) Edwin Hubble's Classification Scheme Elliptical Galaxies E0 E3 E5 E7 Spiral Galaxies S0 Sa Sb Sc SBa SBb SBc The Cosmos: Astronomy in the New Millennium (with CD-ROM and InfoTrac), Second Edition Jay M. Pasachoff, Williams College Alex Filippenko, University of California, Berkeley ISBN: 0-534-39549-X © 2004 Available Now! 432 pp. 8 1/2 x 10 7/8. Paperbound. 4-Color. Non-InfoTrac Version ISBN 0-534-39550-3 1. A Grand Tour of the Heavens. Galaxies, galaxies collide and merge. Solar Systems, Universe 2. Light, Matter, and Energy: Powering the Universe. 3. Light and Telescopes: Extending Our Senses. 4. Observing the Stars and Planets: Clockwork of the Universe. 5. Gravity and Motion: The Early History of Astronomy. 6. The Terrestrial Planets: Earth, Moon, and Their Relatives. The more dense terrestrial planets Mercury,Venus, Earth and Mars cooled nearest the sun. 7. The Jovian Planets: Windswept Giants. The less dense, more gaseous Jovian planets Jupiter, Neptune, Saturn, Uranus stabilized farther from the sun. 8. Pluto, Comets, and Space Debris. 9. Our Solar System and Others. 10. Our Star: The Sun. 11. Stars: Distant Suns. 12. How Stars Shine: Cosmic Furnaces. 13. The Death of Stars: Stellar Recycling. 14. Black Holes: The End of Space and Time. 15. The Milky Way: Our Home in the Universe. 16. A Universe of Galaxies. Lobe radio galaxies emit radio radiation from regions that are typically much more than 10 times_ in size than the visible galaxy. The radio lobes of lobe radio galaxies are truly enormous. From end to end, an entire lobe radio galaxy typically is more than 10 times the size of the Milky Way Galaxy, comparable in size to the entire Local Group. 17. Quasars and Active Galaxies. quasar Star-like radio source with an observed redshift that indicates extremely large distance from Earth. Quasar host galaxies are hard to see because they are so much fainter than the quasar itself. Quasars are also known as quasi-stellar objects because of their unimpressive appearance at visible wavelengths. quasars now known is that their spectra all show large redshifts, ranging from 0.06 (that is, a 6 percent increase in wavelength). As a young galaxy developed and its central black hole used up its fuel, the luminosity of the nucleus diminished. While still active, this galaxy no longer completely overwhelmed the emission from the surrounding stars. The result was an active galaxy-either radio or Seyfert-still emitting a lot of energy, but now with a definite "stellar" component in its spectrum. The central activity continued to decline. Eventually, only the surrounding galaxy could be seen-a normal galaxy, like the majority of those we now see around us. Today, the black holes lie dormant in galactic nuclei, producing only a relative trickle of radiation. Occasionally, two normal galaxies may interact with one another, causing a flood of new fuel to be directed toward the central black hole of one or both. The engine starts up again for a while, giving rise to the nearby active galaxies we observe. 18. Cosmology: The Birth and Life of the Cosmos. 19. In the Beginning. 20. Life in the Universe. Fluorine is a gas is one of the most reactibe elements known. 1.Text Book: Introduction to general, Organic and Biological Chemistry, (4th ed.) by Ouellette; 2.Lab. Manual: Experiments in General, Organic and Biological Chemistry, (4th ed.) by Ouellette; 3.Lab. Packet: OSU-N Lab. Packet (Terri Jackson) (Optional) Study Guides: Student's Guide and Solution Manual, (4th ed.) by Bailey Office Lab Room Phone E-mail Web Site F-2189 F-2177 614-292-4093 x 321 1-800-9-NEWARK andriani.1@osu.edu http://newark.osu.edu/sandriani Office Hours: Monday, Wednesday 3:00 - 5:00 pm; Tuesday 2:00 - 3:30 pm 1.Text Book: Introduction to general, Organic and Biological Chemistry, (4th ed.) by Ouellette; 2.Lab. Manual: Experiments in General, Organic and Biological Chemistry, (4th ed.) by Ouellette; 3.Lab. Packet: OSU-N Lab. Packet (Terri Jackson) (Optional) Study Guides: Student's Guide and Solution Manual, (4th ed.) by Bailey Lecture Days and Time Lecture Room Laboratory M W 5:30 - 7:10pm Founders 2180 T 5:30 - 8:30pm LECTURE SCHEDULE FOUNDERS 2180 Week Lecture Chapter quiz* June 23 Chemistry, Matter, Measurements 1,2 June 30 Measurements, Atomic Structure 2 1 July 7 Periodic Table 3,4 Wednesday, July 9 First Examination July 14 Ionic Compounds, Molecules 4,5 2 July 21 Molecular Geometry, Equations 5,6 3 July 28 Reactions 6,7 Wednesday, July 30 Second Examination August 4 Stoichiometry 7,8 4 August 11 Gases, Liquids, Solids, Solutions 9,10 5 August 18 Rates, Acids and Bases 10,11 Wednesday, August 20 Third Examination August 26 Acids and Bases 11 Elmo Mawk. These notes are intended for Chemistry 107 students only. 1 Chapter 2 The Atomic Nature of Matter Atomic Theory The modern atomic theory is composed of 4 main points. 1. All matter is composed of tiny particles called atoms. 2. All atoms of a given element have identical chemical properties that are characteristic of that element. 3. Atoms form chemical compounds by combining in whole number ratios. (VERY IMPORTANT) 4. Atoms can change how they are combined, but they are neither created nor destroyed in chemical reactions. Conservation of Atoms and Mass. Atoms are neither created nor destroyed during physical or chemical processes. All atoms have mass, so…… Mass is neither created nor destroyed during physical or chemical processes. Mass and atoms are always conserved. Conservation Law - a statement that some quantity is conserved. Wood burns. The ash left over weights less than the original wood. Is conservation of mass violated? No, the missing mass is present as carbon dioxide, water vapor and other gases. Wood + oxygen ‡ ash + smoke Mass is conserved. Atoms combine to make molecules Atoms combine in whole number ratios. Why whole number ratios? Atoms are “uncuttable” - you can not have a partial atom in a molecule. Whole atoms or no atoms at all. Hydrogen and oxygen combine in two different ways. 2H2 + 2O2 ‡ H2O2 Peroxide Copyright 2003, Elmo Mawk. These notes are intended for Chemistry 107 students only and may not be reproduced for profit in any way. 2 2H2 + O2 ‡ 2H2O Water The water and peroxide contain the same elements, but the whole number ratios are different. Peroxide ‡ 1H:1O Water ‡ 2H:1O Atomic Structure Atoms are composed of protons, neutrons and electrons. The protons and neutrons are found in the nucleus. The nucleus is the center of the atom. The electrons surround the nucleus and inhabit most of the space in an atom. Name Symbol Charge Mass Electron e -1.6022 x 10 -19 C 9.1094 x 10 -31 kg Proton p +1.6022 x 10 -19 C 1.6726 x 10 -27 kg Neutron n 0 1.6749 x 10 -27 kg Almost all of the mass of an atom is found in the nucleus. Elements - an element is identified by the charge on its nucleus. The protons are responsible for the charge on the nucleus. This means the number of protons identifies an element. The number of protons in an atom is called the atomic number, Z. Before we stated that the periodic table is laid out in order of increasing mass. The periodic table is laid out in order of increasing mass, but primarily laid out in order of increasing Z number. Isotopes The number of neutrons an atom can contain is variable and doe not change the identity of the atom. The sum of the number of protons and the number of neutrons is the mass number of an atom. An element can have various mass numbers. Each atom within an element that has a different mass number is called an isotope of an element. To designate an isotope, use the following convention. Z A X or ZX or X - A 3 Where X is the element abbreviation, A is the mass number and Z is the atomic number. Example: there are three isotopes of C. 12 C, 13 C, 14 C or C-12, C-13, C-14 Z number is often left off because the chemical abbreviation implies the Z number. (You can look it up on the periodic table). Some isotopes have special names. 2 H and 3 H 2 H is also called deuterium. 3 H is called tritium. Used in fusion bombs. Chemically isotopes are the same, but they can have different radioactive properties. Tritium is the only isotope of hydrogen that is radioactive. Natural Abundances Each element has an isotopic abundance which is independent of the form of the element or where the samples originated. I.E. Carbon has the same isotopic abundance in College Station as it does in Antarctica. Titanium has the following isotopic abundance: 8.2% Ti-46, 7.4% Ti-47, 73.8% Ti-48, 5.4% Ti-49 and 5.2% Ti-50. Mass Spectrometry - instrumentation technique used to determine the isotopic abundances. The sample is charged to form ions; the ions are accelerated and then deflected by a magnetic field. The more massive ions are deflected least; the least massive ions are deflected most. The ions are spread out (sorted) and by varying the voltage; a mass can be selected for detection. See figure 2-19 in your text for a diagram of a mass spectrometer. Ions Ions are charged atoms (monatomic ions) or charged groups of atoms (polyatomic ions). We will discuss monatomic ions for now. Ions are formed by adding or removing an electron. When an electron is removed, a positive ion called a cation is formed. When an electron is added, a negative ion called a anion is formed. Na ‡ Na + + e - cation formed Cl + e - ‡ Cl - anion formed The charge on both sides of these processes must sum up to be the same. For the sodium, on the left, the overall charge is zero; on the right the overall charge is zero. For the chlorine, the overall charge on both sides of the process is negative one. Ionic Compounds Compounds can be formed from ions. These are called ionic compounds. Ionic compounds contain whole numbers of cations and anions and are electrically neutral. Ionic compounds are also called salts. 2Na (s) + Cl2 (g) ‡ 2NaCl (s) Above is an example of a reaction forming an ionic compound. You can predict if a compound is ionic or not if it contains a metal and a nonmetal. Group IA metals form +1 cations. Group IIA metals form +2 cations. Some Group IIIA metals form +3 cations. Transition metals form variable changed cations. Example iron forms Fe 2+ and Fe 3+ . Some Group VA nonmetals form -3 anions. Group VIA nonmetals form -2 anions. Group VIIA nonmetals form -1 anions. Ionic Solutions If an ionic compound is soluble - will dissolve in water - it will dissociate into ions and form a homogeneous mixture. Cations and anions will be surrounded by a cage of water molecules. See Figure 2-24 in your text. Dissolved salts are the reason tap water which contains dissolved salts will conduct current. Forms of Energy 5 There are various forms of energy. The unit of energy is the Joule, J. Sometimes the Calorie, Cal is used. Kinetic Energy - the energy of motion KE = 1 2 mv 2 where m is the mass in kg and v is the speed in m/s. 1 J = 1kgm 2 /s 2 Thermal Energy - energy due to the motion of molecules in an object even when the object is at rest. When heat is added to an object, the molecules move faster. Related to KE. Thermal energy is related to temperature. The higher the temperature, the faster the molecules move. The lower the temperature, the slower the molecules move. Potential Energy - stored energy - in the form of position (gravitational) and chemical. A rock sitting on the side of a hill contains stored energy (tip the rock and it rolls down the hill, converting the potential energy into kinetic energy). Chemical Energy - potential energy- energy stored in the chemical bonds of molecules. Electrical Energy - result of electrical forces between charges Eelect = k q1q2 r where k is a constant, q1 and q2 are the positive and negative charges and r is the distance between the charges. Radiant Energy - energy contained in electromagnetic radiation. (sunlight). Conservation of Energy Energy is neither created nor destroyed in any process, although it may be transferred from one body to another or changed from one form into another. Thermal energy flows from a hot body to a cooler body. A rock sitting in the sun absorbs radiant energy, converting it to thermal energy. A rock on the side of a hill converts its stored potential energy into kinetic energy as it rolls down a hill. A compound burns, releasing the stored chemical energy in the form of heat, and light. Uranium For Nuclear Fission Atomic Number: 92 Atomic Symbol: U Atomic Weight: 238.029 Electron Configuration: [Rn]7s25f36d1 History (Planet Uranus) Yellow-colored glass, containing more than 1% uranium oxide and dating back to 79 A.D., has been found near Naples, Italy. Klaproth recognized an unknown element in pitchblende and attempted to isolate the metal in 1789. The metal apparently was first isolated in 1841 by Peligot, who reduced the anhydrous chloride with potassium. Sources Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. The United States Department of Energy purchases uranium in the form of acceptable U3O8 concentrates. This incentive program has greatly increased the known uranium reserves. Uranium can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament. Properties Uranium exhibits three crystallographic modifications as follows: alpha --(688C)--> beta --(776C)--> gamma. Uranium is a heavy, silvery-white metal which is pyrophoric when finely divided. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis. Isotopes Uranium has sixteen isotopes, all of which are radioactive. Naturally occurring uranium nominally contains 99.28305 by weight 238U, 0.7110% 235U, and 0.0054% 234U. Studies show that the percentage weight of 235U in natural uranium varies by as much as 0.1%, depending on the source. The US DOE has adopted the value of 0.711 as being their official percentage of 235U in natural uranium. Natural uranium is sufficiently radioactive to expose a photographic plate in an hour or so. Much of the internal heat of the earth is thought to be attributable to the presence of uranium and thorium. Uranuim-238 with a half-life of 4.51 x 109 years, has been used to estimate the age of igneous rocks. The origin of uranium, the highest member of the naturally occurring elements - except perhaps for traces of neptunium or plutonium, is not clearly understood. However it may be presumed that uranium is a decay product of elements with higher atomic weight, which may have once been present on earth or elsewhere in the universe. These original elements may have been formed as a result of a primordial creation, known as the big bang, in a supernova, or in some other stellar processes. Uses Uranium is of great importance as a nuclear fuel. Uranium-238 can be converted into fissionable plutonium by the following reactions: 238U(n, gamma) --> 239U --(beta)--> 239Np --(beta)--> 239Pu. This nuclear conversion can be brought about in breeder reactors where it is possible to produce more new fissionable material than the fissionable material used in maintaining the chain reaction. Uranium-235 is of even greater importance because it is the key to utilizing uranium. 235U, while occuring in natural uranium to the extent of only 0.71%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone. Uranium-235 can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive. Natural uranium, slightly enriched with 235U by a small percentage, is used to fuel nuclear power reactors to generate electricity. Natural thorium can be irradiated with neutrons as follows to produce the important isotope 233U: 232Th(n, gamma)--> 233Th --(beta)--> 233Pa --(beta)--> 233U. While thorium itself is not fissionable, 233U is, and in this way may be used as a nuclear fuel. One pound of completely fissioned uranium has the fuel value of over 1500 tons of coal. The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. The estimated world-wide capacity of the 429 nuclear power reactors in operation in January 1990 amounted to about 311,000 megawatts. Uranium in the U.S.A. is controlled by the U.S. Nuclear Regulatory Commission. Uranium is used in inertial guidance devices, in gyro compasses, as counterweights for aircraft control surfaces, as ballast for missile reentry vehicles, and as a shielding material. Uranium metal is used for X-ray targets for production of high-energy X-rays; the nitrate has been used as a photographic toner, and the acetate is used in analytical chemistry. Crystals of uranium nitrate are triboluminescent. Uranium salts have also been used for producing yellow "vaseline" glass and glazes. Uranium and its compounds are highly toxic, both from a chemical and radiological standpoint. Recently, the natural presence of uranium in many soils has become of concern to homeowners because of the generation of radon and its daughters. fishkill.html KING5.com | Local News What's killing the fish in Lake Washington?

    06/18/2003

    By GARY CHITTIM / KING 5 News

    SEATTLE Residents and county agents say they often find large amounts of dead fish this time of year and figure it's a natural die-off. But some scientists aren't so sure.

    It started happening late last week and while county officials are investigating, officials did not comment to KING 5 News yet. At this point they don't seem sure why it's happening.

    You have to get close to the water to see the sunken graveyard of hundreds of Lake Washington fish, their shiny bodies stacked up on the bottom. But you don't have to get close at all to know they are washing up on the shore.

    *
    KING
    Visitors to Juanita Beach will have to get used to stepping over decaying carcasses.
    Carcasses of the dead fish are strewn all over the beach. It's not just little perch, but also big fish such as carp.

    Even the birds cannot keep up with the mess.

    County water experts and others say this is probably a natural event & low oxygen levels in the water due to high temperatures for several days.

    But they are finding that oxygen levels are not all that low and it usually only affects small fish like perch.

    So, what's this all about?

    Captured in pictures from KING 5s helicopter SkyKing were dozens of large, dead fish, apparently carp, in the middle of some discolored water on the north end of the lake, with even bigger live fish swimming nearby.

    The area's famous birds – eagles and herons – watch and wait for their turn to move in.

    Fish and wildlife agents are checking out the situation. At this point some suspect it may be more than the typical seasonal die-off, but could be caused by oxygen-robbing materials like yard fertilizer. More tests are needed and park users will have to get used to stepping over decaying carcasses.

    http://www.king5.com/ The Seattle Times: State: Fish kill probably natural
    Local News: Friday, June 20, 2003

    State: Fish kill probably natural

    By Eric Sorensen
    Seattle Times staff reporter

    http://seattletimes.nwsource.com/cgi-bin/PrintStory.pl? document_id=135039828&zsection_id=268448406&slug=perch20m&date=20030620">

    County and state officials are waiting for results on water samples from Lake Washington's Juanita Bay but say a recent fish kill there probably is a natural event and not caused by pollutants.

    "By all accounts we see it as a pretty naturally occurring situation," said Logan Harris, a spokesman for the King County Department of Natural Resources.

    The county office is awaiting results from a regularly scheduled water sample taken Monday and tests on samples drawn Wednesday and yesterday, said Ben Budka, water-quality/trouble-call coordinator.

    Budka said a review of his notes from last year showed a large perch kill occurred on Lake Washington around June 26.

    "To me this just seems like your typical seasonal fish kill of perch and there's also some sticklebacks," Budka said. He said the first report of this year's fish kill came to him on June 10.

    The state departments of Ecology and Fish and Wildlife also are awaiting results of the water-quality tests, but spokesmen for both agencies were not particularly worried.

    There have been other reports, too, of dead fish where Interstate 90 crosses the lake between Bellevue and Mercer Island.

    In the Juanita Bay area, "there's nothing to indicate there is a pollution event involved here," said Larry Altose of the Department of Energy.

    Moreover, there has been little rain, which would help pollutants make their way into the bay, Altose said.

    Several factors may be involved in the die-off, Altose said. Lake perch have been spawning, putting them under stress.

    Recent warm and sunny weather could have created a localized algae bloom that robbed the water of dissolved oxygen.

    The DNR's Budka saw an oily sheen in the area and is having a sample of it tested for hydrocarbons. But he said he thinks it is a natural sheen put out by the wetland and vegetation near Forbes Creek.

    Eric Sorensen: or esorensen@seattletimes.com

    http://seattletimes.nwsource.com/
    E-mail

    Grow Crystals Materials Alum, about four ounces (about 112 g). Alum is available in the spice section of most grocery stores in 1.9 oz. containers. Alum is not toxic but is very astringent. Salt, about four tablespoons (130 g) Glass containers (four one-pint mason jars or small Pyrex beakers) Thread (regular sewing thread, about three feet [1 m]) A hot-plate or similar apparatus Water Magnifiers such as a binocular microscope, magnifying glass, or hand lens Samples of mineral crystals (quartz, halite and calcite would be good) and of igneous rocks (for example granite, rhyolite, basalt, and gabbro) are optional but suggested. Water Epsom salts A piece of glass Dissolve some of the Epsoms salts in the water. Pour a few drops of the liquid on a piece of glass and let it evaporate in a warm place to produce beautiful crystals. Examine them under a magnifying glass or a microscope. The slower crystals grow, the more perfect they grow. Photographed through a glovebox window, this single crystal of the superconductor plutonium-cobalt-pentagallium was formed using the flux-growth technique. The method used to grow the single crystals discussed in this article is the flux-growth technique, which was initially championed by Zachary Fisk in the early 1980s. The technique involves dissolving the constituent elements of the desired compound in an excess of a low-melting metal‹a flux; a process analogous to growing sugar crystals from supersaturated water solutions in high school chemistry. The Los Alamos researchers grew their plutonium superconductor from excess gallium, but they have also grown single crystals from excess indium and antimony. To grow the crystals, the researchers place the starting material, including the excess flux, in an alumina crucible that is sealed in an evacuated quartz ampoule. The sealed ampoule is heated to high temperature (about 1,000 degrees Celsius) and then cooled slowly over one or two days to an intermediate temperature of about 600 degrees Celsius. At this point, a centrifuge is used to separate the solid crystals from the excess liquid flux. The resulting crystals are well faceted, large (about 1 gram of total mass is not difficult to achieve), and of high quality. Critical Mass: The exact amount of material needed to sustain a fission chain reaction. Fission: A reaction in which a neutron causes the nucleus of an atom to split in two fragments. This reaction also causes the release of energy as well as more neutrons. Fission chain reaction: A chain reaction occurs when the neutrons released during fission cause other nuclei to split and release more neutrons. The process is repeated; large amounts of energy are released during this reaction. A chain reaction is like a domino system where the first domino knocks down two dominos and each of those dominos knocks down two more dominos, etc. Fissionable: Material, like the isotopes Uranium-235 and Plutonium-239, that are unstable and can undergo the fission reaction. Fusion: A second type of nuclear reaction where nuclei combine to form a large nucleus. During this reaction, energy is also released. Implode: Collapse inward (opposite of explode). Implosion is caused when explosives are detonated on the outside of an object, which causes a shockwave to travel inward and crush the object. Isotope: The name given to atom that has acquired or lost one or more neutrons from its nucleus. The atom's structure is relatively the same, but the added or subtracted weight may cause the atom to have new properties (such as being fissionable). Plutonium-239: P-239 is a man-made and unstable isotope of plutonium, discovered by Glen Seaborg. It also has the capability of undergoing a fission chain reaction. Supercritical: When the amount of fissionable material is greater than the amount needed to sustain a fission chain reaction., the result is a large amount of energy, because of the excess material, which causes an explosion. Uranium-235: U-235 is a rare and unstable isotope of uranium ore. It has the capability of undergoing a fission chain reaction. Cady Coleman EDUCATION: Graduated from W.T. Woodson High School, Fairfax, Virginia, in 1978; received a bachelor of science degree in chemistry from the Massachusetts Institute of Technology in 1983, and a doctorate in polymer science and engineering from the University of Massachusetts in 1991. The Extraordinary Chemistry of Ordinary Things, 3rd Edition by Carl H. Snyder (Author) Availability: Usually ships within 1-2 business days 17 used & new from $15.95 Edition: Hardcover 2.6 Isotopes: Deuterium and Tritium 29 As an illustration, a common atom of the element fluorine has a mass number of 19 and an atomic number of 9. its nucleus is made up of 9 protons and 10 neutrons. 19 - 9 =10.. Because all atoms must be electrically neutral, we know that there are as many electrons surrounding the fluorine atom's nucle- us as there are protons within its nucleus, or 9 of each. Moreover, since the chemical symbol for fluorine is F, we can represent the atom as F How Many Neutrons? How many neutrons are there in the nucleus of a sodium atom of mass number 23? The atomic number of sodium is 11. With an atomic number of 11, Z = 11 for sodium. Since the mass number of this particular atom of sodium is 23, A=23, knowing that the number of neutrons = A - Z. neutrons = A - Z neutrons = 23 - 11 neutrons = 12 The nucleus of this sodium atom contains 12 neutrons. The most common kind of beryllium atom, atomic number 4, has a mass num- ber of 9. How many protons are there in the nucleus of this berylium atom? How many neutrons? How many electrons surround the nucleus? Given that the chemical symbol for berylium is Be show 4 Z, and the symbol as we did in the example of fluorine? 2.6 Isotopes: Deuterium and Tritium As we have seen, the atomic nucleus can contain neutrons as well as protons. An atom with one proton and also a single neutron in its nucleus is an atom of hydrogen with a mass number of Z. It must be an atom of the element hydro- gen because with one proton in its nucleus its atomic number is 1 and all atoms with an atomic number of 1 belong to the element hydrogen. But its mass number must be 2 since both the proton and the neutron contribute 1 atom each to the total mass. Deuterium is the so-called heavy hydrogen. used in the construction of the hydrogen bomb. see chapter 4. Naturally occurring deuterium is extremely rare, there's only about one deuterium atom for every 6700 hydrogen atoms of mass number 1 that occur. Isotopes are atoms of the same element with different mass numbers. Table 2-2 Electron Structures of the First 20 Elements Element Symbol Atomic Number Quantum Number of Shell 1 2 3 4 Hydrogen H 1 1 Helium He 2 2 Lithium Li 3 2 4 Berylium Be 4 2 2 Boron B 5 2 3 Carbon C 6 2 4 Nitrogen N 7 2 5 Oxygen O 8 2 6 Fluorine F 9 2 7 Neon Ne 10 2 8 Sodium Na 11 2 8 1 Magnesium Mg 12 2 8 2 Aluminum Al 13 2 8 3 Silicon Si 14 2 8 4 Phosphorus P 15 2 8 5 Sulfur S 16 2 8 6 Chlorine Cl 17 2 8 7 Argon Ar 18 2 8 8 Potassium K 19 2 8 8 1 Calcium Ca 20 2 8 8 2 30 Chapter 2 Atoms and Elements There is one deuterium atom Hydrogen mass 1 Deuterium mass 2 Naturally occurring hydrogen consists almost entirely of only the two isotopes protium and deuterium. It's possible to manufacture a third isotope, tritium, by adding a second neutron to the nucleus. Tritium with a nucleus containing one proton and two neutrons has a mass number of 3 and an atomic number of 1. Tritium is used along with deuterium to produce the explosive force of the hydrogen bomb. Question As we've just seen, an atom with a nucleus consisting of one proton and two neutrons is tritium, an isotope of hydrogen. Is an atom with a nucleus consisting of pne neutron and two protons still another isotope of hydrogen? Explain your answer. 2.7 Building up the Elements: Hydrogen through Neon 31 H Hydrogen He Helium Li Lithium Be Beryllium B Boron C Carbon N Nitrogen O Oxygen F Fluorine Ne Neon all the helium atoms in the universe have two neutrons in their nuclei as well as two protons. Helium mass number is 4. atomic number is 2. 2.7 Hydrogen through Neon in its nucleus a helium atom has two negatively charged electrons in the sur- rounding shell. These two electrons completely fill this particular shell; no more electrons can enter it. We're familiar with helium as a gas used to fill bal- loons. Since helium is less dense than air, helium filled balloons tend to rise upward into the atmosphere. A third proton produces lithium, atomic number 3 and for the most com- mon isotope mass number 7. Lithium is a metal used in small long lasting batteries that power digital watches, calculators, and similar electronic equip- ment. Adding the proton to the nucleus requires adding a third electron to maintain electrical neutrality. Since the shell containing the first two electrons is now full and can hold no more electrons, the third electron goes into a sec- ond shell, larger than the first and concentric with it. Each of these electron shells occupied by the electrons that surround the nucle- us is called a quantum shell and receives a quantum number: 1 for the shell closest to the nucleus filled by two electrons 2 for the next shell which can hold a maximum of eight electrons, 3 for the next, and so forth. We use the term electron structure to indicate the distribution of electrons in the quantum shells surrounding a nucleus. RELATED CONCEPTS Students should have previously studied the particulate nature of matter and the concept of atoms as building blocks of matter. RELATED SKILLS Use of calculator for exponential numbers. PERFORMANCE OBJECTIVES After completing their study of atomic structure, students should be able to: 1. show the interrelationships of atomic number, atomic mass, numbers of protons, neutrons, and electrons. 2. describe the relative energies of ultraviolet, visible, infrared, microwave, X-ray, radio, and TV waves. 3. determine the electron configuration of a specified neutral atom. 4. draw an orbital diagram that correlates with a given electron configuration. 5. identify the maximum number of electrons that can occupy a shell or set of orbitals. 6. distinguish between absorption (excitation) and emission of energy.
    Make your own free website on Tripod.com