PH104 Descriptive Astronomy Learning Objectives March 11, 2008 1 Introduction This list of questions are questions that will need to be answered in order for students to be successful in the course. Each exam will be drawn from the same topics as these questions. The questions on the exams will either be verbatim or similar in content. 1.1 Material Integration Here is the layout for the midterms. Midterm 1 will be primarily section 1 and section 2 of the multiple choice and questions 1-18 of the written section. Midterm number 2 will be primarily section 2 and section 3 of the multiple choice and questions 19-33 of the written section. The Final will cover all of the material in that I will draw questions directly from this document for each section. Keep in mind that there may be a need to use your knowledge from previous material, but I will not ask any specific questions from that material. 2 Multiple-Choice Below is a list of multiple-choice questions that may show-up on the exams. I will break these down into sections based upon the topic that they are most 1
related with. Keep in mind that the science or physics topics can show up in all of the other subsequent topics. 2.1 The Nature of Science and Physics These questions relate to the nature of science and the straight forward topic of physics. 1. When the space probe Voyager II passed by Saturn, its speed increased (but it did not fire any rocket or engine). What must have happened? 2. The amount of gravitational potential energy that an object has available to convert to kinetic energy when it falls depend on... 3. Momentum is calculated using what variables? 4. As long as an object is not gaining or losing mass, a non-zero outside force on the object will cause a change in what quantity? 5. What is a scientific model? 6. (This question does not have a list, but it will if on an exam. You should know as much as you can about scientific models). Given a list of statements which one about scientific models is true? 7. What is Newton s first law of motion? 8. What is Newton s second law of motion? 9. What is Newton s third law of motion? 10. Suppose you kick a soccer ball up to a height of 10 meters. According to conservation laws, when will the gravitational potential energy of the ball be the greatest? 11. Suppose an object is moving in a straight line at 50 m. According to hr Newton s first law of motion what can you predict about the future of the object? 12. Angular momentum is calculated using what three quantities? 2
13. What is light? 14. How do I use light to find the chemical composition of an astronomical body like a star? 15. A person is reading a newspaper while standing 5 feet from a table with an unshaded 100 watt light bulb. If the person were to move to 10 feet from the table, how many light bulbs will be needed to light up the newspaper with the same amount of brightness? 16. How does the speed of radio waves compare to the speed of visible light waves? 17. I have two electromagnetic waves. Wave A has a wavelength of 750 nm. Wave B has a wavelength of 350 nm. Which electromagnetic wave will have the higher energy? 18. The light year is a unit of 19. How do we define the astronomical unit? 20. A volleyball has about half the mass of a basketball. If both are moving the same velocity, how does the volleyball s kinetic energy compare to the basketball s kinetic energy? 21. Electrons in atoms will change from a low energy orbital to a high energy orbital through an interaction with what? 22. I want to measure the x-ray emission from the Sun. Which telescope would I use? 23. What is Kepler s first law? 24. What is Kepler s second law? 25. What is Kepler s third law? 26. How do we calculate density? 27. What is the best measure of the validity of an astronomical or any other hypothesis? 28. What is Occam s razor? 3
29. What does the semi-major axis of an orbit measure? 30. When we say something is periodic, what do we mean? 31. What does parallax measure? 32. How long does it take the Moon to go through a full set of phases? 33. What is the celestial sphere? 34. What is a photon? 35. What is the main difference between a neutron and a proton? 36. What is the main difference between an electron and a proton? 37. What is the nucleus of an atom? 38. What are the major hallmarks of science that we will use in this class? 39. What force holds the protons in an atom s nucleus? 40. How do we define the electromagnetic force? 41. What is a parsec? 42. What unit would we use to describe the size of an atom? 43. (This one may have different numbers than are here, but the concept is the same). Multiply 3 10 6 and 5 10 6. 44. Since angular momentum is conserved, what will happen to the angular speed of a large gas cloud as it collapses? 45. How does the Earth s orbital speed at closest approach to the Sun compare to Earth s orbital speed at furthest approach? 46. How does Earth s orbital speed at closest approach to the Sun compare to Mars orbital speed at closest approach? 47. The planets never travel in a straight line as they orbit the Sun. According to Newton s second law of motion, what does this mean? 48. Compared to your mass on Earth, your mass on the Moon will be... 4
49. How does light tell us the speed of distant objects? 50. Gravity... 51. When a photon interacts with an atom what changes occur? 52. What is the center of mass of an object? 53. What equation do we use to calculate the gravitational force between two objects. 54. How do we calculate the surface gravity of an object? 55. What equation would we use to calculate the mass of a body using orbital motion? 56. How would we calculate the escape velocity of an object? 57. What is the primary cause for the ocean tides of Earth? 58. As a result of the Moon s gravitational pull, when would you weigh less? 59. How do we explain the tidal bulge on the side of the Earth opposite to the Moon? 60. What is a conservation law? 61. What is an inverse-square law? 62. What is the definition of a ground state? 63. What is a spectrum? 64. How would we calculate the energy of a photon? 65. How would we measure the wavelength of light? 5
2.2 The Solar System This list is primarily concerned with definitions and laundry type lists of information from the planets. Most of these things will come from the reading. I will not overly cover these things in the lectures. Make sure you read the chapters on the planets so that you can be prepared. 1. What features separate the Jovian planets from the Terrestrial Planets? 2. In the lab, you found that the orbit of the Moon is an ellipse, which law does this best fit with? 3. Why do we need to be concerned with the exceptions to the rules of the Solar System? 4. What is a terrestrial planet? 5. Using the given list, which planets are mostly rocky with iron cores? 6. More than 99% of the Solar System is contained in... 7. What is the Kuiper Belt? 8. What is accretion? 9. What do we think creates the magnetic field on Earth? 10. What is atmospheric pressure? 11. What is the most abundant element in the Earth s atmosphere? 12. How do astronomers think the Moon formed? 13. What evidence is there for the large impact formation of the Moon? 14. Why is Venus s surface hotter than Mercury s? 15. What is the runaway greenhouse effect 16. What is the main gas in the atmosphere of Mars? 17. How big is the radius of Mars compared to Earth? 6
18. What evidence is there for liquid water on Mars in the past and present? 19. What are asteroids? 20. Where can most of the asteroids be found? 21. What are factors cause the main difference in the terrestrial planets? 22. How does distance from the Sun affect a planet? 23. The composition of the atmospheres of Jupiter and Saturn are closest to the composition of what other solar system body? 24. Why does Jupiter radiate more heat than we would expect? 25. Besides the Sun, which Solar System body has the greatest mass? 26. Why are Uranus and Neptune blue? 27. How do the compositions of Uranus and Neptune differ from the composition of Jupiter 28. What feature of Uranus would cause some astronomers to think Uranus has undergone a giant impact early in its history? 29. Why do why experience seasons on Earth? 30. What is the definition of a year? 2.3 Stars This is the section that will have to do with stars. The second midterm will consist of mainly stars and stellar models. 1. Sirius B is a white dwarf star. On the HR diagram, where would I place it? 2. Using the HR diagram, what type of stars are white dwarfs? 3. Using the HR diagram, where would we find the most massive mainsequence stars? 7
4. Using the HR diagram, where would we find the oldest main-sequence stars? 5. Using the HR diagram, where would we find the dimmest stars? 6. What region is the closest to where the Sun would be located on the HR diagram? 7. Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? 8. Which of the following stellar properties can you estimate simply by looking at a star on a clear night? 9. Since angular momentum is conserved, the rotational speed of a collapsing gas cloud 10. What do we mean by the event horizon of a black hole? 11. You are looking at the stars in the constellation of Orion from your backyard. Can you tell which stars are hotter than the others? 12. Red giant stars have greater than 10,000 times the luminosity of our yellow Sun. What property of red giant stars would cause this to be the case? 13. We plot the thermal spectra of two stars. Which one is hotter? 14. Why does hydrogen fusion not occur in stars under 0.08 Solar Masses? 15. In 10 billion years what will the Sun be like? 16. The upper mass limit for a white dwarf is 17. In a high mass main sequence star the dominant fusion cycle is the CNO cycle. What is happening in this cycle? 18. When the star begins to evolve off of the HR diagram, it will slowly become a red giant. What visible changes are happening to the star 19. What does the luminosity of a star measure? 20. The hottest stars are what color? 8
21. The special theory of relativity implies what about time? 22. If by some unknown process the Sun suddenly collapsed in on itself and became a black hole tomorrow, the planets would 23. What is a main-sequence star? 24. A person is at rest, while you are moving by them at a speed almost the speed of light. You shine a flashlight on that person. How will your measurement of the speed of the flashlight beam be in comparison to the person at rest? 25. There is a relation between the mass and luminosity of MS stars. More luminous MS stars are more massive. What color would the most massive MS stars be? 26. Which of the following stellar properties can you estimate simply by looking at a star on a clear night? 27. If two intrinsically identical stars are at different distances from the Earth, the more distant star will have a 28. The star Betelgeuse is about 500 light years away from us in the constellation Orion. If this star underwent a supernova explosion right now, approximately how long would it be until we found out about it? 29. How far from the Earth is the nearest star? 30. Two identical stars, one 5 light years from Earth, and a second 50 light years from Earth are discovered. How much fainter does the farther star appear to be? 31. The reason astronomers use the concept of the absolute magnitude is to allow stars to be compared directly removing the effects of differing 32. What causes light from a star to be Doppler-shifted? 33. We can detect the velocity of a star through the Doppler effect by 34. Which of the following stars is probably oldest? 35. Giant stars are more rare than main sequence stars because 9
36. A star evolves off the main sequence when 37. A star is burning hydrogen to helium in its core and has ten times the mass of the Sun. Which of the following are true? 38. After hydrogen fusion stops in the core of a star, the core 39. As a one solar mass star evolves into a red giant, its 40. When a star becomes a red giant it becomes much brighter because it is 41. If the temperature in the core of the Sun increased 42. If the rate of hydrogen fusion within the Sun were to increase, the core of the Sun would 43. After a star has evolved into a red giant, hydrogen burning 44. Angular momentum plays an important role in star formation. What characteristics of stars are strongly affected by angular momentum? 45. Which of the following statements about apparent and absolute magnitudes is true? 46. What is a main-sequence star? 47. In a low mass star the dominant fusion cycle is the pp chain in which hydrogen is fused into what element? 48. Knowing what we know about stellar evolution now, it is safe to say that the Sun formed within an open cluster some 5 billion years ago. 49. During star formation the disk around the star will begin to flatten out. What is causing this to happen? 50. What is causing a star like the Sun to shine? 51. Angular momentum plays an important role in star formation. What characteristics of stars is strongly affected by angular momentum? 52. The axes on a Hertzsprung-Russell (H-R) diagram represent 10
53. How does light tell us the temperature of stars? 54. Using the HR diagram given, where would we find the oldest mainsequence stars? 55. The radius of Betelgeuse is about 2.5 AU. If we put this star where the Sun is, where would its surface end up? 56. You are looking at the stars in the constellation of Orion from your backyard. Can you tell which stars are furthest from you? 57. In the lab, you found the mass of Uranus. What information would you need in order to find the mass of Jupiter using the same techniques. 58. Which of the following statements about black holes is not true? 59. Given the mass of a star, discuss the life stage of the star. 60. Discuss what it would be like to visit a black hole. 61. What is a cepheid variable? 62. What is a RR lyrae star? 3 Galaxies and Cosmology This part is about galaxies and cosmology. Cosmology is the study of the cosmos, so in a sense we have been doing cosmology since the beginning of the course. But the cosmology that we are studying here is a specific type. 1. The largest identifiable structures in the universe are 2. The cosmological principle enables astronomers to generalize from what they observe to the properties of the universe as a whole. The principle states that any and all observers, everywhere in space, should see, on average, the same picture of the universe as us on scales comparable to 3. Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest? 11
4. What is the significance of the Planck time? 5. Which one would astronomers use as a standard candle 6. A large galaxy contains mostly old population II stars spread throughout its volume, but has little dust or gas. What type of galaxy is this most likely to be? 7. Astronomers think that dark matter exits because 8. Why do we call dark matter dark? 9. Gravitational bending of light can be used to 10. Suppose a white dwarf is gaining mass at a relatively high rate due to accretion in a binary system. What happens when the mass reaches the 1.4-solar-mass limit? 11. The cosmic background radiation comes from a time in the evolution of the universe 12. In which direction is the cosmic background radiation the brightest? 13. What is meant by inflation in the early universe? 14. Dark Energy is... 15. What does it mean for the expansion of the universe if dark energy does not exist? 16. Cepheid variables are important for astronomers because 17. What is a galaxy? 18. How do we find the size of the Milky Way Galaxy? 19. How do we find the Earth s position in the Milky Way Galaxy? 20. How big is the Milky Way galaxy? 21. What is the Milky Way galaxy shaped like? 22. What is the definition of a population II star? 12
23. What is the definition of a population I star? 24. What are the differences between Pop I and Pop II stars? 25. What are Pop III stars? 26. What is the definition of a dark nebula? 27. What is the definition of a reflection nebula? 28. How does dust in the interstellar regions affect our ability to observe the Milky Way? 29. What is the mass of the Milky Way? 30. Why do we hypothesize that there is a supermassive black hole in the center of the Milky Way galaxy? 31. What is the definition of dark matter? 32. Why do we call dark matter dark? 33. What is a spiral galaxy? 34. What is an elliptical galaxy? 35. What is an irregular galaxy? 36. What is a dwarf galaxy? 37. How far away is the closest galaxy to the Milky Way? 38. How far away is the closest spiral galaxy to the Milky Way? 39. What is a barred spiral galaxy? 40. What is the difference between a group of galaxies and a cluster of galaxies? 41. What is a QUASAR? 42. What is a radio lobe galaxy? 43. What are the three types of data astronomers gather to help confirm the existence of dark matter? 13
44. What might dark matter be? 45. What is a MACHO? 46. What is a WIMP? 47. What is a gravitational lens? 48. What is meant by the term dark matter halo? 49. What is the meaning of cosmological redshift? 50. What problems are solved by a period of inflation in the universe? 51. Where does the helium in the early universe come from? 52. What is the cosmological constant? 53. What is Omega(Ω) 14
4 Written Questions Half of each exam will be concerned with you answer in short answer form. Short answers can be... One or two sentence answers. Labeled diagrams Data analysis Small non-calculator calculations With this format of exam, all students can show their strengths or weaknesses. I again will break the list of items into sections. 1. Draw a labeled diagram of the Bohr model of the hydrogen atom. 2. You are living in a different star system with a certain number (to be given in the exam) of planets. You want to develop a model of this star system in order to be able to discuss its formation. Given the information for each planet, develop a classification model that groups the planets into main types. This is similar to what we have done for the Solar System. 3. Given three spectra of an atom, determine which is stationary with respect to the observer, which one is moving toward the observer, and which one is moving away from the observer. Also determine which one is moving the fastest compared to the others. 4. In one sentence, explain how speed, frequency, and wavelength of an electromagnetic wave are related. 5. Draw a labeled diagram of an electromagnetic wave. 6. Given a set of data that represents the angular positions of a planet in orbit around a star. Two of the data points are when the planet is at its closest point and two data points represent when the planet is at its furthest point. Using your knowledge of Kepler s second law, which two data points are the closest point to the star, and which two data points are the furthest from the star? Show your work. 15
7. Given a table that shows the orbital radius and orbital speed (velocity at the time data taken) of a planet around a star. Using this table you should be able to determine whether this planet is or is not conserving angular momentum, and why you would answer that. 8. In two sentences, what does Newton s first law tell us about the difference between motion in a straight line and motion on a curved line. 9. In one sentence, what does Kepler s second law tell us about the orbital speed of a planet? 10. In one sentence, what does Kepler s third law tell us about the differences in Jupiter and Mars? 11. In one sentence, explain the relationship between light and distance. 12. In no more than two sentences explain why the structure of an atom leads to discreet energy levels. 13. In no more than two sentences explain how we would use spectra to locate hydrogen in the universe. 14. In one sentence define frequency. 15. In no more than three sentences explain the differences between an absorption spectrum and an emission spectrum. Include a discussion of how each one is formed. 16. Given a set of data about a fictional star system (similar to lab 2), discuss where and at what temperature compositional changes take place in this star system. 17. Given a set of data about the position of a planet in its orbit (similar to pre-lab 3), discuss whether or not this planet obeys Kepler s law. 18. How would we find the mass of a planet? This should be a discussion of what data we would need to take and what relation or relations we would apply to that data. You can do this in no more than three sentences. 16
19. What is a planetary nebula? Explain the properties of the star, and what is happening to cause it to look like it does in the sky. No more than 3 sentences. 20. 28. In no more than 2 sentences explain how we would find the mass of a black hole or neutron star. Equations are allowed as answers. 21. Explain how mass determines the main-sequence lifetime of a star. No more than 2 sentences. 22. What is left after a planetary nebula completely dissipates? One sentence only. 23. Why does the thermal pressure holding up a star drop when iron is formed from fusion. No more than 2 Sentences. 24. In no more than 2 sentences explain how we would find the mass of a black hole or neutron star. Equations are allowed as answers. 25. Explain how mass determines the main-sequence lifetime of a star. No more than 2 sentences. 26. What is left after a planetary nebula completely dissipates? One sentence only. 27. Why does the thermal pressure holding up a star drop when iron is formed from fusion. No more than 2 Sentences. 32. Given the stars in table 1 fill in the table with the appropriate properties. When comparing to the Sun, the answer will be greater than or smaller than the Sun. You may find the HR diagram in question 27 useful. When a space is not applicable write none. When preparing, remember that the list may be different than the one given here. 28. Given a list of stellar properties, describe the units that we normally use for those properties and how we would measure the value of each for the Sun or another star. 29. Given a periodic set of data about a star (either a set for orbit or a set for brightness change), build a model of the period, maximum value, minimum value, and average value. Discuss how the data indicates that the star is orbiting something or not. 17
Star Mass Main-Sequence Approximate Surface Approximate Lifetime Effective Color Radius Temperature Brown Dwarf Arcturus A 10 Solar Mass Main Sequence Star A stellar corpse Table 1: Stellar Property Table 30. In one sentence describe what the Doppler effect is. In one other sentence describe how we use the doppler effect in astronomy. 31. Given a set of stellar data and an HR diagram, describe where those stars are in their evolutionary stages (i.e. early, middle, late, or stellar corpse). 32. Given an HR diagram draw a line that represents the stages of life of the Sun. Mark the... 1. protstar stage 2. main-sequence stage 3. first red giant stage 4. second red giant stage 5. planetary nebula stage 6. white dwarf stage on the diagram. 18
33. Given a list of objects and the measurements of their calcium K line, determine whether the object is moving toward us, moving away from us, or sitting still with respect to us. 34. Explain in 2 sentences what a standard candle is, and how we would use it. 35. Explain in 2 sentences where the microwave background radiation came from, and why it is important. 36. Explain in 2 sentences why inflation is important in the Big Bang model, and what problems inflation fixes. 37. Draw a labeled diagram of how a foreground galaxy can gravitationally lens light, and next to it, what an Einstein cross might look like in the sky? 38. Draw a labeled diagram of the rotation curve of the Milky Way Galaxy, and explain in no more than 2 sentences why this implies the existence of dark matter. 39. There are three different redshifts that we see in astronomy: Doppler redshift, Gravitational redshift, and Cosmological redshift. In no more than 3 sentences explain what causes each one to happen. 40. Given different values of the redshift (z) of galaxies, determine which ones are moving away faster and which ones are further away. 41. Given a list of the distance and recessional velocities of 6 galaxies: plot these values, and show how one would find the Hubble constant for those six galaxies. 42. Discuss in no more than 2 sentences how the value of the Hubble constant gives us the age of the universe. 43. Discuss in no more than 3 sentences how cosmologists have built a model of the formation and evolution of the universe. 44. Explain what the value of the cosmological constant implies about the universe? 19
45. Given 5 spectra of galaxies, determine which ones are closer, and which ones are moving away faster. 46. Given a diagram with three lines that represent a relation between distance and recessional velocity choose the one that best represents Hubble s Law. Using that line fill in the values asked for below. 20