NAME _____________________________ ID # ____________ LAB # ________
Astronomy 1001 - Final Exam Dr. Leonard Kuhi - Spring 2000
Read Instructions Carefully:
The essay questions of this exam are graded by more than one person, so it is imperative that your NAME BE LEGIBLY WRITTEN ON EACH PAGE OF THE ESSAY PORTION!
1. MARK THE ANSWERS YOU CHOOSE ON THIS TEST AS IT IS YOUR ONLY
OPPORTUNITY TO CHECK WHICH ANSWERS YOU GOT RIGHT OR
WRONG. This will not be done for you at a later time in the departmental office.
Exams will be returned to the alphabetical boxes in the North wall of the Physics
building approximately 3-4 days after the exam.
2. Print your NAME, ID # and SECTION # on your answer sheet where appropriate. Your
SECTION # should read 02. All three items are necessary for the proper scoring and
computer transfer of your scores.
3. Use a pencil, make your marks dark and neat, and erase thoroughly.
4. There is only one answer to each question. Choose the best answer.
5. You may use this test for scratch paper.
6. You are allowed one page (both sides) of notes.
7.
I. Multiple Choice (3 pts. each)
1. At approximately what time would a first quarter moon rise?
a) 6 a.m. b) 9 a.m. c) noon d) 6 p.m. e) midnight
2. The wavelength of a wave is
a) how strong the wave is
b) the distance between a peak of the wave and the next trough
c) the distance between two adjacent peaks of the wave
d) the distance between where the wave is emitted and where it is absorbed
e) equal to the speed of the wave times the wave’s frequency
3. When an electron in an atom goes from a higher energy state to a lower energy state, the atom
a) emits a photon of a specific frequency
b) absorbs a photon of a specific frequency
c) absorbs several photons of a specific frequency
d) can emit a photon of any frequency
e) can absorb a photon of any frequency
4. Spectra from neutral atoms compared with spectra from ionized atoms of the same element
a) are the same
b) are slightly redshifted
c) are slightly blueshifted
d) have different sets of spectral lines
e) have the same sets of spectral lines but different widths for those lines
5. Studying the spectrum of a star can tell us a lot. All of the following statements are true except one. Which one?
a) the peak of the star’s thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths
b) the total amount of light in the spectrum tells us the star’s radius
c) we can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals
d) we can look at Doppler shifts of spectral lines to determine the star’s speed toward or away from us
e) we can determine the temperature of the star’s photosphere
6. When does a star become a main-sequence star?
a) when the protostar forms from a molecular cloud
b) the instant when hydrogen fusion first begins in the star’s core
c) when the rate of hydrogen fusion within the star’s core is high enough to maintain hydrostatic equilibrium
d) when a star becomes luminous enough to emit thermal radiation
e) when hydrogen fusion is occurring throughout a star’s interior
7. Why does a star grow larger after it exhausts its core hydrogen?
a) the outer layers of the star are no longer gravitationally attracted to the core
b) hydrogen fusion in a shell source outside the core generates enough thermal pressure to push the upper layers outward
c) helium fusion in the core generates enough thermal pressure to push the upper layers outward
d) helium fusion in a shell source outside the core generates enough thermal pressure to push the upper layers outward
e) the internal radiation generated by the hydrogen fusion in the core has heated the outer layers enough that they can expand after the star is no longer fusing hydrogen
8. What is a planetary nebula?
a) a disk of gas surrounding a protostar that may form into planets
b) what is left of the planets around a star after a low-mass star has ended its life
c) the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star after its red giant phase
d) the molecular cloud from which protostars form
e) the expanding shell of gas that is left when a white dwarf explodes as a supernova
9. Which of the following is closest in size (radius) to a white dwarf?
a) the Earth b) a small city c) a football stadium d) a basketball e) the Sun
10. What happens when the gravity of a massive star is able to over come neutron degeneracy pressure?
a) the core contracts and becomes a white dwarf
b) the core contracts and becomes a ball of neutrons
c) the core contracts and becomes a black hole
d) the star explodes violently, leaving nothing behind
e) gravity is not able to overcome neutron degeneracy pressure
11. Which event marks the beginning of a supernova?
a) the onset of helium burning after a helium flash in a star with mass comparable to that of the sun
b) the sudden outpouring of X-rays from a newly formed accretion disk
c) the sudden collapse of an iron core into a compact ball of neutrons
d) the beginning of neon burning in an extremely massive star
e) the expansion of a low-mass star into a red giant
12. After a supernova event, what is left behind?
a) always a white dwarf
b) always a neutron star
c) always a black hole
d) either a white dwarf or a neutron star
e) either a neutron star or a black hole
13. Which of the following is closet in size (radius) to a neutron star?
a) the earth b) a city c) a football stadium d) a basketball e) the Sun
14. From a theoretical standpoint, what is a pulsar?
a) a star that alternately expands and contracts in size
b) a rapidly rotating neutron star
c) a neutron star or black hole that happens to be in a binary system
d) a binary system that happens to be aligned so that one star periodically eclipses the other
e) a star that is burning iron in its core
15. What kinds of objects lie in the halo of our galaxy?
a) open clusters b) O and B stars c) globular clusters d) gas and dust e) all of a-d
16. What kinds of objects lie in the disk or our galaxy?
a) open clusters b) O and B stars c) old K and M stars d) gas and dust e) all of a-d
17. Which of the following statements about black holes is not true?
a) if you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits (or reflects) becomes more and more redshifted.
b) if we watch a clock fall toward a black hole, we will see it tick more and more slowly as it falls closer to the black hole
c) a black hole is truly a hole in spacetime, through which we could leave the observable universe
d) if the Sun magically disappeared and was replaced by a black hole of the same mass, the Earth would soon be sucked into the black hole
e) if you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.
18. How do we know that there is much more mass in the halo of our galaxy than in the disk?
a) there are so many globular clusters in the halo that their total mass is greater than the mass of stars in the disk
b) stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk
c) although the question of mass in the halo was long mysterious, we now know it exists because we see so many brown dwarfs in the halo
d) the recent discovery of photinos, combined with theoretical predictions, tells us that there must be a huge mass of photinos in the halo
e) we don’t know that there is more mass in the halo; it is only a guess based on theory
19. What evidence supports the theory that there is a black hole at the center of our galaxy?
a) we observe an extremely bright x-ray source at the center of our galaxy
b) we can see gas falling into an accretion disk and central mass at the center of our galaxy
c) the motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across
d) we observe a large, dark object that absorbs all light at the center of our galaxy
e) all of a-d
20. 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?
a) the one that is reddest in color
b) the one that is bluest in color
c) the one that is farthest away
d) the one that is closest to us
e) the one that appears smallest in size
21. What is the major difference between an elliptical galaxy and a spiral galaxy?
a) a spiral galaxy contains mostly younger stars
b) a spiral galaxy has a spherical halo
c) an elliptical galaxy lacks a disk component
d) elliptical galaxies are not as big as spiral galaxies
e) there are no dwarf spiral galaxies, but there are dwarf ellipticals
22. How was Edwin Hubble able to use his discovery of a Cepheid variable star in Andromeda to prove that the “spiral nebulae” were actually entire galaxies?
a) there are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy
b) he measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy
c) he used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy
d) From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy
e) since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way
23. What is Hubble’s law?
a) the longer the period of time between peaks in brightness, the greater the luminosity of the Cepheid variable star
b) the recession velocity of a galaxy is directly proportional to its distance from us
c) the recession velocity of a galaxy is inversely proportional to its distance from us
d) the faster a spiral galaxy’s rotation speed, the more luminous it is
e) the faster a spiral galaxy’s rotation speed, the less luminous it is
24. What do scientists mean by the critical density of the universe?
a) the minimum density that a universe needs in order to form galaxies
b) the precise density marking the dividing line between a universe that has enough mass to contract again and a universe that will continue to expand forever
c) the minimum density that a universe needs in order to form stars
d) the average density of the space between galaxies
e) the minimum density that a universe needs in order to create hydrogen
25. What is a quasar?
a) a star-like object that actually represents a bright patch of gas in the Milky Way
b) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a cluster of galaxies
c) a specialized astronomical instrument for observing distant stars
d) the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
e) another name for very bright stars of spectral type O
26. Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically follows?
a) Dr. X believes that the universe is expanding, but Dr. Y does not
b) Dr. X believes that the Andromeda Galaxy ( a member of our Local Group) is moving away from us at a slower speed than Dr. Y believes
c) Dr. X believes that the universe is older than Dr. Y believes
d) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever
e) Dr. X believes that the universe has a much higher density than Dr. Y believes
27. How do observations of distant galaxies help us learn about galaxy evolution?
a) observations at different distances show galaxies of different ages and therefore different stages of evolution
b) we can observe the birth of galaxies
c) we can observe the evolution of a single galaxy over time
d) we can observe two galaxies merging and what the result is, helping us learn how mergers affect evolution
e) we can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance
28. Why should galaxy collisions have been more common in the past than they are today?
a) galaxies were more active in the past and therefore would have collided with each other more frequently
b) galaxies were much bigger in the past since they had not contracted completely
c) galaxies were closer together in the past because the universe was smaller
d) galaxies attracted each other more strongly in the past because they were more massive ; they had not yet turned most of their mass into stars and light
e) galaxy collisions shouldn’t have been more common in the past than they are now
29. What evidence suggests that the Milky Way contains dark matter?
a) we observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see
b) we see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way
c) we see many dark voids between the stars in the halo of the Milky Way
d) when we observe in different wavelengths, such as infrared or radio, we see objects that don’t appear in visible-light observations
e) when we look at the galactic center, we are able to observe a large black hole that is composed of dark matter
30. Why wasn’t the intracluster medium in clusters of galaxies discovered until the 1960s?
a) we did not know how much dark matter existed before then
b) we didn’t have the resolution to observe galaxy clusters until then
c) the Milky Way was blocking our view of distant galaxy clusters
d) the medium emits X-rays, which are blocked by the Earth’s atmosphere and require X-ray satellites in space in order to be observed but there were no such satellites in 1960
e) radiation emitted by the medium was so dim that we couldn’t detect it until we built much larger telescopes
31. What do we mean by inflation?
a) what happened the instant after the Big Bang
b) a sudden expansion of the universe after the strong force froze out from the GUT force
c) the expansion of the universe that we still observe today
d) the sudden release of photons when a particle and antiparticle annihilate each other
e) the separation that occurs after two photons collide and create a particle and an antiparticle
32. Why is the era of nucleosynthesis so important in determining the chemical composition of the universe?
a) all the elements except hydrogen were produced after the era of nucleosynthesis
b) we can observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe
c) except for the small amount of matter produced later by stars, the chemical composition of the universe is the same now as at the end of the era of nucleosynthesis
d) we can study the processes that occurred during the era of nucleosynthesis to determine how most of the elements in the universe were created
e) by knowing how much matter was created during the era of nucleosynthesis, we can determine whether the universe is open or closed
33. Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are true. Which one is fictitious?
a) the cosmic background radiation is expected to have a temperature just a few degrees above absolute zero, and its actual temperature turns out to be about 3 K (actually 2.7 K)
b) the cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction
c) the cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does
d) the cosmic background radiation is expected to look essentially the same in all directions, and it does
e) the cosmic background radiation is expected to have tiny temperature fluctuations at the level of about 1 part in 100,000. Such fluctuations were found in the COBE data.
34. Why do we expect the cosmic background radiation to be almost, but not quite, the same in all directions?
a) the overall structure of the universe is very uniform, but the universe must have contained some regions of higher density in order for galaxies to form
b) the temperature of the universe can be found by taking an average over the entire sky, but individual stars will create peaks in the spectrum over small angles
c) dark matter consisting of WIMPs greatly smooths out the spectrum, but the small patches of “light” matter create peaks in the spectrum
d) the overall structure of the universe is very uniform, but the synthesis of different elements produces varying signatures within the background spectrum
e) the overall structure of the universe is very uniform, but intervening gas between us and the era of nuclei absorbs wavelengths depending on the composition and redshift of the gas
35. Some recent but still preliminary measurements of the expansion rate of the universe suggest a problem with our standard idea about how the universe should be expanding. What is the problem?
a) the measurements suggest that the universe may not be expanding at all
b) the measurements suggest that the universe may be shrinking rather than expanding
c) the measurements suggest that the expansion may actually be accelerating, rather than slowing under the influence of gravity
d) the measurements indicate that the universe is at least 30 billion years old, meaning that more than 10 billion years passed between the Big Bang and the formation of the first stars and galaxies
e) the data suggest that the expansion rate varies widely in different parts of the universe
NAME _____________________________ ID # ____________ LAB # ________
Astronomy 1001 - Final Exam Dr. Leonard Kuhi - Spring 2000
II. Essay Questions (Total 105 points):
1. (20) The figure shows the HR diagrams for four different clusters; the dashed lines refer to the location of the Sun. Which cluster is the oldest? Which cluster is the youngest? Which cluster is about 10 billion years old? In each case give the reasoning behind your answer.
(continued on back)
NAME _____________________________ ID # ____________ LAB # ________
Astronomy 1001 - Final Exam Dr. Leonard Kuhi - Spring 2000
2. (10) Why do all the photos of asteroids taken by NASA spacecraft show a relatively smooth surface rather than the jagged and sharp-edged features shown in many movies?
3. (10) Describe what is meant by the term “ultimate recycling” as used in class in reference to the Milky Way.
NAME _____________________________ ID # ____________ LAB # ________
Astronomy 1001 - Final Exam Dr. Leonard Kuhi - Spring 2000
4. (15) Give an example from the Solar System to indicate the likely future in store for the Earth if we continue in our present ways with respect to the environment. Be as specific as you can in explaining the reasons for your choice.
5. (20) What do we mean by a “Standard Candle?” Why is having one so important? What is used as a standard candle to measure the distances to the most distant galaxies? Describe how it is used.
(continued on back)
NAME _____________________________ ID # ____________ LAB # ________
Astronomy 1001 - Final Exam Dr. Leonard Kuhi - Spring 2000
6. (15) In class we discussed ten recent discoveries in astronomy. Pick any one of these discoveries and describe its importance to our understanding of that particular field.
7. (15) What was the hardest thing for you to grasp or believe of all the things we talked about in class? Why? [This question has no specific correct answer; I just want to know what you think.]