Astronomy 1143 Final Exam Review Answers Prof. Pradhan April 24, 2015 What is Science? 1. Explain the difference between astronomy and astrology. 2. What number is the metric system based around? What are some of the more widely-used prefixes? 3. What special attribute of certain constellations puts them in the zodiac? Observational Astronomy: The Night Sky 1. What is the ecliptic plane? 2. Why is the ecliptic tilted with respect to the celestial equator? How big is this tilt in degrees? 3. Where does the ecliptic plane intersect the celestial equator? 4. What are the primary coordinates for finding a place on Earth? How about the celestial sphere? 5. In what constellation would you find Polaris? 6. What is the angular size of an object? What is it for the Moon? 7. How big is an arcminute? An arcsecond? 8. What is stellar parallax? Why is it useful? 9. Why couldn t the ancient Greeks see parallax, and what did they think this meant? 10. What is a parsec? How many light years are in a parsec? The Heliocentric Model 1. In simple terms, what are the geocentric and heliocentric models? 2. Who was the first major proponent of the heliocentric model? What were the key facets of his model? 3. Explain the main observational problem that Mars presented for the Geocentric and early Heliocentric models. 4. What did Ptolemy add to the geocentric model explain this problem? 5. Who correctly solved this problem? How? Using whose data? 6. Which of Galileo s observations supported the heliocentric model? 1
7. What else did Galileo discover with the telescope? 8. Define: superior planet, inferior planet, conjunction, opposition, quadrature, perihelion, aphelion, and eccentricity. 9. Venus is on the opposite side of the Sun compared to the Earth. What is the name for this configuration of an inferior planet? 10. What is a synodic period of a planet? Sidereal period? 11. Are planetary orbits perfectly circular as proposed by Kepler? 12. Explain Kepler s 3 Laws. 13. What is the proportionality between period and semimajor axis in Kepler s 3rd Law? 14. Whose observations did Kepler use in order to come up with his laws of planetary motion? Forces, Accelerations, and Laws of Motion 1. What are Newton s Three Laws of Motion? 2. What is inertia? 3. What is the equation that governs the gravitational attraction between two bodies? 4. Explain Kepler s 3 Laws. 5. What is the proportionality between period and semimajor axis in Kepler s 3rd Law? 6. Why do things with mass feel heavy here on Earth? 7. Is weight, or how heavy something feels, a force or a mass? 8. What determines how fast an object falls toward the Earth when dropped? 9. What is the gravitational acceleration of the Earth, g, and who first measured it? 10. What are the units for force, mass, and acceleration? Light 1. What is light? 2. How is light created and what can light interact with? 3. How is the wavelength of light related to its frequency? 4. What are the units for frequency and wavelength? 5. List the electromagnetic spectrum from highest energy to lowest energy. Note that this is also the list from shortest wavelength to longest wavelength, and the list from highest frequency to lowest frequency. 6. Do different wavelengths of light travel at different speeds in the same medium? 7. What wavelength range is visible light? 8. List the visible colors in order of increasing frequency (increasing energy and decreasing wavelength). 9. How does the energy of a photon relate to other properties of light? 2
Atoms and Spectroscopy 1. What subatomic particles make up the atom? 2. Which subatomic particle is most important for determining which element an atom is? 3. How many protons, electrons, and neutrons does a hydrogen atom have? 4. Can electrons be anywhere around the nucleus? 5. What happens when an atom emits light? What is the energy of that light? 6. What happens when an atom absorbs light? Can an atom absorb light of any energy? 7. What does an emission spectrum look like, in general, for a single element? 8. What does an absorption spectrum look like, in general, for a single element? 9. What are some of the most well-known emission and absorption series of lines of hydrogen, and what part of the electromagnetic spectrum are they in? 10. What can you learn from looking at the spectrum of a star? 11. What is a blackbody? 12. What is temperature? 13. What is absolute zero? Doppler Effect 1. What causes the Doppler effect? 2. What kinds of waves exhibit the Doppler effect? 3. If a star has an emission line at a particular wavelength λ, will the observed wavelength be longer or shorter if the star moving away from us? What color will this emission line be shifted toward? Relativity 1. What are the two postulates of relativity? 2. How is the energy of an object related to its mass? 3. Why can t objects move at the speed of light? 4. What is the important idea in general relativity? 5. What are time dilation and space contraction? 3
Telescopes 1. Why do we use telescopes? 2. What is the difference between a refracting and a reflecting telescope? 3. What happens when light passes through a lens? 4. Where is the best place to put a telescope? 5. How does the power of a telescope scale with its diameter? 6. What is the purpose of a telescope s eyepiece? 7. List a few of the important telescopes in use today. Stars 1. What is a star? 2. What is the H-R Diagram? 3. How are the luminosity, radius, and temperature of a star related? 4. What other properties of a star increase when the star s mass increases? 5. What determines the color of a star? 6. How do we classify stars? 7. Which layer of a star is the part that we see? 8. What is a globular cluster? Hertzsprung-Russell Diagram and Luminosity Relations 1. What does a star s location on the HR diagram tell us? 2. What is the main sequence? 3. Where is the red giant sequence on the HR diagram? What does this location mean? 4. What is the most important stellar property that determines all other properties of a star? 5. How does a star s radius and temperature relate to its luminosity? 6. How does a star s aparent brightness relate to its luminosity? Spectral Types of Stars 1. What is the spectral sequence of stars, from hottest to coolest? 2. What color are hot stars? Cool stars? 3. What causes stars to have a specific color? 4. Do O and B type stars show hydrogen lines in their atmospheres? 5. What spectral type is the Sun? What is the Sun s effective temperature? 6. What part of the spectrum does most of the Sun s light come out in? 4
Figure 1: The Hertzsprung-Russell diagram. Note that temperature increases to the left. The line through the middle is the main sequence, the lower line is the white dwarf sequence, and the lines in the upper right are the red giant and supergiant sequences (supergiant is on top). Life of Low Mass Stars 1. What is the mass cutoff for a low mass star? 2. How does a low mass star spend most of its life? 3. What happens when a low mass star stops fusing hydrogen? 4. What is the maximum mass that a white dwarf can have? What is this mass called? What happens if this mass is exceeded? 5. What is a white dwarf? 6. What is the largest element a low mass star can fuse in its core? Life of High Mass Stars 1. What happens to a high mass star after the main sequence? 2. What is a neutron star? Supernovae 1. How massive does a star have to be in order to end its life in a supernova? 2. What causes a core-collapse supernova? Our Universe 1. Is the universe expanding, contracting, or staying the same? How do we know this? 2. What do we mean when we say the universe is expanding? 5
3. If everything in the universe is expanding away from us, does this mean we re at the center of the expansion? 4. What is Hubble s Law? 5. Using Hubble s law, how can we determine the age of the universe? 6. Using Hubble s constant, how can we determine the size of the observable universe? 7. What is the important caveat to using Hubble s Law and Constant to determine the age and size of the universe? 8. What is the Cosmic Microwave Background? 9. How do we know there s dark matter? 10. What are the most abundant elements in the universe? 11. What does a flat rotation curve of galaxies tell us? 12. What is Olbers Paradox? What is the resolution? 13. What is the 21-cm line and why is it useful for cosmology? Cosmological Distance Ladder 1. What is the Distance Ladder? 2. On what is each step of the Distance Ladder calibrated? 3. List the rungs, or methods, of the Distance Ladder by increasing distance. The Big Bang Model 1. What is the Big Bang Model? 2. What is some observational evidence for the Big Bang? 3. How old is our universe? Expansion, Mass, and Density of the Universe 1. How do we know the universe is expanding? 2. What makes up the mass-energy of the universe? 3. What is dark energy? 4. What drives the expansion of the universe? 5. What slows down the expansion of the universe? 6. What is the critical density? 7. What is the parameter Ω (called omega )? 8. How do the different mass-energies of the universe contribute to the value of Ω? 6
9. If the density of matter (dark and light) divided by the critical density is 0.3 (currently measured to be true), what would happen if there was no dark energy to make up the other 0.7 to get Ω = 1? 10. What happens to the photons in the universe as the universe expands, and how does this impact the amounts of matter and radiation in the universe? 11. How do we measure the expansion of the universe and how it changes over the age of the universe? Large Scale Structure 1. What is large scale structure? 2. Does structure in the universe increase or decrease as the universe grows older? 3. Why doesn t the expansion of the universe due to dark energy destroy large scale structure? 4. The Cosmic Microwave Background is very smooth, meaning it is pretty much the same temperature everywhere. However, we see large scale structure in our universe. Why is it hard to reconciliate these two facts, and what is the solution? 5. What are the largest structures in the universe? Galaxy Classification 1. Who first came up with the galaxy classification system, and what is it based on? 2. What are the types of galaxies in the classification system? 3. How old are the stars in each type of galaxy? 4. What kind of galaxy is the Milky Way? Exoplanets and Life in the Universe 1. What is necessary for life as we know it? 2. What was the experiment that showed a primitive atmosphere can produce amino acids? 3. What is necessary for reproduction of living organisms? 4. What is the Drake Equation, and which parameters in it can we actually observe? 5. In general, do astronomers think it s possible for there to be lifeform like those on Earth elsewhere in our galaxy? Why or why not? 6. What are the ways we determine a star might have a planet orbiting it? 7. What is direct imaging of a planet? 8. What is the easiest kind of planet to find with all of the detection methods? 9. How do planets form? 10. How is our Solar System different from other planetary systems we ve found? Why is this a problem for planetary formation theory? 11. Are planets possible around metal-poor stars? 7