Download Exam # 3 – Tue 12/06/2011

Exam # 3 – Tue 12/06/2011
Astronomy 100/190Y – Exploring the Universe — Fall 11
Instructor: Daniela Calzetti
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INSTRUCTIONS: Please, use the `bubble sheet’ and a pencil # 2 to answer the exam
questions, by marking the appropriate bubble for each question.
Write your last and first name and Student ID on the `bubble sheet’, and mark them in the
bubbles. Use of textbook and class notes is allowed.
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1. The Sun is:
A. a protostar
B. a main sequence star
C. a red giant
D. a planetary nebula
E. a white dwarf
2. The Sun is luminous because it is:
A. releasing gravitational energy
B. releasing hydrostatic pressure energy
C. fusing hydrogen into helium in its core
D. fusing hydrogen into helium in a shell right outside the core
E. fusing helium into carbon
3. The Sun’s life expectancy is:
A. 107 years
B. 108 years
C. 109 years
D. 1010 years
E. 1011 years
4. The most important characteristic of a star for determining its lifetime is
A. radius
B. luminosity
C. mass
D. distance from the main sequence
E. temperature
5. A star that is 10 times more massive than the Sun is
A. 3,000 times more luminous
B. 300 times more luminous
C. 30 times more luminous
D. more or less as luminous as the Sun
E. 3 times less luminous than the Sun
6. A star that is 10 times less massive than the Sun has a lifetime that is
A. 300 times shorter than that of the Sun
B. 3 times shorter than that of the Sun
C. more or less the same length as that of the Sun
D. 3 times longer than that of the Sun
E. 300 times longer than that of the Sun
7. A white dwarf has high temperature and
A. is bright relative to a hot main sequence star because it has a small radius
B. is bright relative to a hot main sequence because it has a large radius
C. we cannot say anything about its brightness
D. is faint relative to a hot main sequence star because it has a small radius
E. is faint relative to a hot main sequence because it has a large radius
8. Stars spend most of their life as
A. protostars
B. main sequence stars
C. red giants
D. planetary nebulae
E. white dwarfs
9. A white dwarf is
A. supported by neutron degeneracy.
B. supported by electron degeneracy.
C. supported by carbon fusion in its center.
D. supported by carbon fusion in a shell.
E. a slowly cooling iron core.
10. A red giant has low temperature and
A. is bright relative to a cool main sequence star because it has a small radius
B. is bright relative to a cool main sequence because it has a large radius
C. we cannot say anything about its brightness
D. is faint relative to a cool main sequence star because it has a small radius
E. is faint relative to a cool main sequence because it has a large radius
11. More massive main sequence stars
A. are more luminous, hotter, and live longer than low mass main sequence stars
B. are less luminous, hotter, and live longer than low mass main sequence stars
C. are more luminous, cooler, and live less than low mass main sequence stars
D. are less luminous, hotter, and live less than low mass main sequence stars
E. . are more luminous, hotter, and live less than low mass main sequence stars
12. A pulsar is
A. a fast rotating, magnetized black hole.
B. a stationary black hole.
C. a stationary, magnetized neutron star.
D. a fast rotating, magnetized neutron star.
E. a fast rotating, magnetized white dwarf.
13. A supernova is caused by:
A. the fusion of hydrogen in shell
B. the fusion of helium in shell
C. the fusion of iron in shell
D. the core collapse of a massive star
E. the core collapse of a low mass stars
14. A white dwarf is
A. supported by carbon fusion in its center.
B. supported by carbon fusion in a shell.
C. a slowly cooling iron core.
D. supported by neutron degeneracy.
E. supported by electron degeneracy.
15. A neutron star is
A. a slowly cooling iron core.
B. a fast rotating black hole.
C. a remnant of a massive star’s collapse.
D. a fast rotating pulsar.
E. a stationary supernova.
16. The `event horizon’ in a black hole is:
A. the radius below which tidal forces are so strong they can rip you apart.
B. the radius below which nothing, not even light, can escape.
C. the radius defining the actual surface of the black hole.
D. the radius at which clocks slow down.
E. the radius that can tunnel you to a parallel Universe.
17. The heaviest elements are produced in:
A. the cores of low mass stars
B. the cores of massive stars
C. the core collapse of massive stars
D. the ejected materials in planetary nebulae
E. the burning shells of massive stars
18. The escape velocity of a body from the surface of a star of mass M and radius R
is given by vesc= (2GM/R)1/2. If the star shrinks without changing mass, the escape
velocity can become so large to equal or exceed the speed of light. In that case,
we have a:
A. black dwarf
B. neutron star
C. black body
D. black hole
E. brown dwarf
19. A white dwarf is hot because
A. it is the core of a dying star
B. it has released energy by ejecting its outer layers
C. it is burning carbon in a shell
D. it is releasing heat from gravitational contraction
E. it is supported by nuclear fusion
20. Parallax would be easier to measure if:
A. the stars were further away
B. Earth moved backward along its orbit
C. Earth’s orbit were larger
D. Earth moved faster along its orbit
E. all of the above.
21. If a star has a parallax of 0.05 seconds of arc, then its distance is:
A. 2 parsecs
B. 5 parsecs
C. 20 parsecs
D. 50 parsecs
E. 500 parsecs
22. What is the order of evolution of a small star like the Sun?
A. red giant, white dwarf, planetary nebula, main sequence.
B. planetary nebula, main sequence, red giant, white dwarf.
C. main sequence, red giant, planetary nebula, white dwarf.
D. white dwarf, main sequence, planetary nebula, red giant.
E. main sequence, red giant, white dwarf, planetary nebula.
23. Binary stars allow us to find the ________ of the stars.
A. colors
B. luminosities
C. surface temperatures
D. masses
E. composition
24. To calculate a star radius you must know its
A. chemical composition and temperature.
B. temperature and luminosity.
C. surface gravity and temperature.
D. color and chemical compositions.
E. chemical composition and luminosity.
25. A neutron star is expected to spin rapidly because
A. it has high orbital velocity
B. it has high density
C. it has high temperature
D. it conserved angular momentum when it collapsed
E. the energy from the supernova explosion that produced it made it spin faster.
26. A supernova explosion occurs when a star
A. exhausts its supply of hydrogen fuel
B. ends its main-sequence phase of life
C. becomes a white dwarf
D. attempts to burn iron in its core
E. produces a planetary nebula
27. Which of the following stars is densest? (recall that density is the mass divided
by the volume)
A. a red giant star
B. a white dwarf
C. a main sequence star
D. a protostar
E. the Sun.
28. Star A has a parallax of 0.2 seconds of arc. Star B has a parallax of 0.04 seconds
of arc. The two stars have identical luminosities. How much brighter or fainter
will appear Star A relative to Star B when observed from Earth?
A. 25 times brighter
B. 5 times brighter
C. they have approximately the same brightness
D. 5 times fainter
E. 25 times fainter.
29. When a star first leaves the main sequence, what is happening in its center?
A. It is burning hydrogen in its core
B. It is burning helium in its core
C. It is burning helium in a shell surrounding an inert carbon core
D. It is burning hydrogen in a shell surrounding an inert helium core
E. All thermonuclear reactions have stopped.
30. Younger stars contain a larger fraction of `heavy’ elements (heavier than helium)
because:
A. the heavy elements where made in previous generations of stars
B. old stars destroy heavy elements as they age
C. young stars burn their nuclear fuels faster
D. heavy elements haven’t had the time to settle into the cores of the younger
stars
E. all of the above
31. Globular clusters are:
A. clusters of stars located in the disks of galaxies
B. clusters of stars located in the bulges of galaxies
C. clusters of the youngest stars in a galaxy
D. clusters of stars located in the haloes of galaxies
E. clusters of the most metal rich stars in a galaxy
32. For which of the following objects does the Hubble Law works?
A. Gas clouds in the Milky Way
B. Nearby stars
C. Galaxies
D. Distant stars
E. All of the above
33. What does the Hubble Law describe?
A. Closer stars move faster away than distant stars
B. Closer galaxies approach faster the Milky Way that distant galaxies
C. Distant stars approach faster than closer stars
D. Distant galaxies move faster away than closer galaxies
E. None of the above.
34. The basic constituents of the Milky Way are
A. the halo, the disk, and the bulge
B. the halo, the disk, and the globular clusters
C. the halo, the disk, and interstellar clouds
D. the halo, the spiral arms, and the bulge
E. the halo, the spiral arms, and the globular clusters.
35. According to the formation theory of the Milky Way:
A. the halo was formed after the disk
B. the spiral arms were formed before the disk
C. the halo was formed before the disk
D. the halo and the disk were formed at the same time
E. the halo and the spiral arms were formed at the same time.
36. What property galaxies, star clusters, and stars have in common? They all
A. are held together by gravity
B. are composed mostly of hydrogen
C. condensed out of gas clouds
D. None of the above
E. All of the above.
37. One problem faced by astronomers in trying to figure our the structure of the
Milky Way is that
A. there is no way to measure distances greater than 120 light years.
B. only a small fraction of the Milky Way is visible because of interstellar dust.
C. the Milky Way looks uniform in all directions from the Earth.
D. the positions of stars in the Milky Way change so rapidly that it is difficult to
produce an accurate picture.
E. our view is blocked by the millions of comets at the periphery of the Solar
System.
38. Our Sun is located:
A. At the center of the Milky Way
B. In the halo of the Milky Way, roughly at the periphery
C. In the halo of the Milky Way, roughly 2/3 of the way between the center and
the edge
D. In the disk of the Milky Way, roughly at the periphery
E. In the disk of the Milky Way, roughly 2/3 of the way between the center and
the edge.
39. Spiral arms are:
A. gravitational waves that attract stars and gas from the surrounding regions
B. pressure waves that compress gas and stars along their path
C. density waves that travel at a different speed from gas and stars
D. electromagnetic waves that modulate the passage of gas and stars
E. A and B.
40. We find mostly hot, massive stars in the spiral arms of galaxies because
A. hot, massive stars are preferentially produced in the spiral arms
B. less massive stars live long enough to rotate out of the spiral arms
C. supernovae destroy the less massive stars in the spiral arms
D. there is too high a density in the spiral arms to create low-mass stars
E. low-mass stars are produced exclusively outside the spiral arms.
41. The Hubble Turning Fork describes:
A. a classification scheme for the appearance of galaxies.
B. the evolution of galaxies from ellipticals to irregulars.
C. a scenario for the formation of galaxies.
D. a classification scheme for the number of stars in a galaxy.
E. a classification scheme for describing the distances of galaxies.
42. The existence of the Hubble Law
A. tells us that the Universe is expanding
B. implies that the Universe had a beginning about 14 billions years ago
C. allows us to measure the distances of galaxies
D. says that more distant galaxies recede more rapidly than nearby ones
E. all of the above.
43. Astronomers use Cepheids to measure galaxies’ distances because
A. the faster they vary, the more distant they are
B. they obey the Hubble Law
C. they are the most common type of main-sequence stars in galaxies
D. they all lie in the same spot of the Hertzsprung-Russell diagram
E. their intrinsic luminosity can be determined from their period of pulsation.
44. An astronomer living in a galaxy far away from us would see:
A. some galaxies coming towards her/him and some moving away from her/him
B. many more nearby galaxies than we do
C. our Milky Way approaching him/her
D. most galaxies coming towards her/him
E. the same relation between redshift and distance that we observe.
45. Which of the following elements does NOT produce energy when fused in the
center of a star?
A. Helium
B. Hydrogen
C. Neon
D. Iron
E. Calcium
SOLUTIONS:
1. B
2. C
3. D
4. C
5. A
6. E
7. D
8. B
9. B
10. B
11. E
12. D
13. D
14. E
15. C
16. B
17. C
18. D
19. A
20. C
21. C
22. C
23. D
24. B
25. D
26. D
27. B
28. A
29. D
30. A
31. D
32. C
33. D
34. A
35. C
36. E
37. B
38. E
39. C
40. B
41. A
42. E
43. E
44. E
45. D