Astro 102 Test 5 Review Spring See Old Test 4 #16-23, Test 5 #1-3, Old Final #1-14

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1 Astro 102 Test 5 Review Spring 2016 See Old Test 4 #16-23, Test 5 #1-3, Old Final #1-14 Sec 14.5 Expanding Universe Know: Doppler shift, redshift, Hubble s Law, cosmic distance ladder, standard candles, Hubble s constant Be able to answer: What 2 observations tell us the universe is expanding? How does an objects red or blueshift relate to the object s movement? How does a galaxy s speed relate to its distance? Does the universe have a center? If we know the Hubble constant, what do we know about the universe? Why is the cosmic distance ladder useful? What are some standard candles? What is look-back time? Chapter 15 Milky Way Section 15.1 Measuring Milky Way Know: globular clusters How can globular clusters help find distances? How far away is the center of the Milky Way? Where is the sun located in the Milky Way? What does the center of the Milky Way have to do with globular clusters? What are some physical characteristics of the Milky Way? Sec 15.2 Evolution of Milky Way Know: heavy elements Are the stars in globular clusters young or old? How do we know? Where are globular clusters found relative to the disk of the Milky Way? How are heavy elements formed? How does the amount of heavy elements in stars change over time? What were the first stars like? Sec 15.5 Galaxy formation Know: protogalaxies How do galaxies form? Which formed first, halo or disk objects? Is the Milky Way still forming stars? Is the Milky Way still growing? What is an example of a protogalaxy around today?

2 Chapter 16 Evolution of the Universe Sec 16.1 Big Bang Know: Big Bang, cosmological redshift, Hubble time Be able to answer: How does the value of the Hubble constant relate to the age of the universe? Where did the Big Bang happen? Do galaxies, stars, etc. expand as the universe expands? What did the universe look like in the past? What was the universe like at the moment of the Big Bang? What causes cosmological redshifts? Sec CMB Know: CMB What is a major prediction of the big bang theory that has been confirmed? What is the cause of the CMB? Who first saw the CMB? How? Why is the temp of the CMB only about 3K? Sec 16.3 Expansion is Speeding Up Know: dark energy, cosmological constant What are some possible fates of the universe? How does gravity affect the expansion of the universe? What things contribute gravity to the universe? If we only look at the amount of gravity in the universe, what is the fate of the universe? What is the evidence for dark energy? Or What is the universe doing that lead to the idea of dark energy? How does dark energy effect the expansion of the universe? If we include gravity and dark energy, what is the fate of the universe? Clicker Questions Ch A bright star is moving away from Earth. Which of the choices best completes the following statement describing the spectrum of this star? A(n) spectrum that is relative to an unmoving star. A. absorption, blueshifted B. emission, redshifted C. continuous, blueshifted D. absorption, redshifted E. continuous, redshifted ANS: D

3 3. The distances to galaxies used to establish Hubble s law are found from: A. radar B. parallax C. Main-sequence fitting D. Standard candles, such as supernovae D 4. The value of H0 is about 72 km/sec/mpc. Suppose it were twice as big. Compared to our current estimates, what would the age of the universe be? A. The same as now. B. Younger. C. Older. B Explanation: The rate of expansion determines when the Big Bang took place. A faster expansion would mean that the separation between objects would have gone to zero sooner in the past. Ch Imagine that you could travel at the speed of light. Starting from Earth, how long would it take you to travel to the center of the Milky Way Galaxy? a) 2 years b) 20 years c) 250 years d) 2,500 years e) 25,000 years ANS: E 2. Where is our Sun located in the Milky Way Galaxy? a) at the exact center b) near the center c) about half way between the center and the outer edge d) near the outer edge ANS: C 3. In general, the Milky Way a. Has the same chemical composition as time passes b. Has more abundant Hydrogen as time passes c. Has more abundant heavy elements as time passes d. Has less abundant heavy elements as time passes Ans: C 4. In the disk of the Milky Way, stars are and dust and gas are than in the halo. a. Younger; more diffuse b. Older; more diffuse c. Older; denser d. Younger; denser D

4 5. The Milky Way galaxy a. Has been exactly the same since it first formed b. Has only changed in number of stars since it first formed c. Is still evolving, consuming nearby galaxies d. Is finished evolving, and will not change any more C Ch Which of the following best describes the Big Bang? a) An outward explosion of matter and energy at the beginning of the universe that threw matter into empty space. b) An outward explosion of matter and energy at the beginning of the universe that threw matter into regions of space where other matter already existed. c) The expansion and cooling of the universe from an originally hot and dense state. d) More than one of the above. ANS: C 2. If you watched the history of the universe like a movie playing backward, what would you see? a) Objects getting farther apart. b) The universe becoming denser. c) The temperature of the universe decreasing. d) Regions of space becoming smaller. e) More than one of the above. ANS: E, (B and D are correct) 3. Name one fact below that by itself does NOT support our idea that the Big Bang happened. A. The existence of the cosmic background radiation. B. That 24% of matter is helium. C. That the universe is expanding. C Explanation: The mere existence of the expansion does not necessarily imply that the universe was once hot and dense. Perhaps the expansion is a recent phenomenon, or the combination of Omegas means that the average separation between matter was never small. The other two observations directly support the idea of the Big Bang. 4. If the fate of the universe were determined SOLELY by what we currently know to be the total mass of the universe in luminous and dark matter (excluding dark energy), astronomers would predict that we live in a universe that will: a. expand forever b. stop expanding and eventually collapse c. slow its expansion but never reverse it d. oscillate between expansion and collapse ANS: A 5. The overall density of the universe decides its ultimate fate, because the more matter in the universe: a. the more black holes will form, which will devour surrounding material more quickly. b. the more gravity there will be to pull the universe together. c. the more massive stars it will contain, and the faster it will evolve d. the more stars it will form over time and the longer the universe will last. Ans: B

5 6. When astronomers discovered that the universe was, they had to revive Einstein s cosmological constant. a. Accelerating b. Expanding c. Contracting d. Decelerating Ans: A