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Exam 2
Astronomy 114
Part 1
[1-40] Select the most appropriate answer among the choices given.
How do astronomers figure out the following properties of stars? Find the matching answer in the
right column.
1.
2.
3.
4.
5.
Distance
Mass
Temperature
Size
Magnetic field
(A) Wien’s Law
(B) Zeeman effect
(C) generalized Kepler’s Law
(D) Stefan-Boltzmann Law
(E) parallax
6. Which of the following objects are not found in the same plane defining the solar system?
(A) planets (B) asteroids (C) the Moon (D) comets (E) the Sun
7. What would you expect the Sun to become eventually?
(A) an M star (B) a neutron star. (C) a white dwarf. (D) a black hole. (E) a supernova.
8. The Sun is made mostly of
(A) hydrogen and helium.
(B) helium and lithium.
(C) hydrogen and carbon.
(D) carbon, oxygen, and nitrogen.
(E) silicon and iron.
9. According to the solar nebular theory, the flat shape of the Solar System results from
(A) a collision of the early system with another cloud that squashed it.
(B) intense magnetic fields in the early Solar System.
(C) curvature of the space and time.
(D) rotation of the original cloud from which it formed.
(E) a super-secret government conspiracy.
10. How would the brightness of a 8th magnitude star compare with a 7th magnitude star?
(A) It is 10 times brighter than the 7th magnitude star.
(B) It is 10 times dimmer than the 7th magnitude star.
(C) It is 2.5 times brighter than the 7th magnitude star.
(D) It is 2.5 times dimmer than the 7th magnitude star.
(E) They have the same brightness.
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11. At the center of the Sun, fusion converts hydrogen into
(A) water and carbon dioxide.
(B) plasma and smoke.
(C) radiation and elements like carbon and nitrogen.
(D) radioactive elements like uranium and plutonium.
(E) helium, energy, and neutrinos.
12. In order to start nuclear fusion, a high temperature is required in the center of a star. This is
to overcome
(A) gravitational force between atoms.
(B) nuclear force between atoms.
(C) degeneracy force between neutrons.
(D) electric repulsive force between protons.
(E) Klingon force field.
13. Sunspots are dark because
(A) they contain so much heavy material that light can’t readily escape.
(B) the solar wind cools the surface locally.
(C) magnetic fields bring iron up from the core which blocks the light.
(D) local magnetic fields reduce convection and the heat reaching the surface.
(E) parts of the Sun are burnt crisp from uneven heat.
14. If the Sun turned into a black hole but kept exactly the same mass it has now, the Earth would
(A) be rapidly pulled in.
(B) be tossed into a much larger and more elliptical orbit.
(C) be broken apart by the intense burst of gamma rays the black hole would emit.
(D) continue to orbit it as before although the Sun would be dark.
(E) fly off into space as the black hole “sucked” in its own gravity.
15. A black hole is invisible by definition. Which of the following would you be able to use to
detect and study the presence of a black hole?
(A) gravitational influence on a companion star.
(B) a dark spot in the field of stars.
(C) X-ray emission from its accretion disk.
(D) all of the above.
(E) only (A) & (C).
16. What is the Chandrasekhar limit?
(A) speed limit for photons
(B) the maximum possible mass of a white dwarf
(C) the distance from the center of the galaxy
(D) the smallest mass of a star can have and still burn hydrogen
(E) the size of a black hole
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17. The age of a star cluster can be determined from
(A) main sequence fitting. (B) main sequence turnoff. (C) pulsating variables. (D) spectroscopic
binaries. (E) visual binaries.
18. All stars begin their lives with the same basic composition. What characteristic mainly determines how bright they become and how long they live?
(A) location (B) mass (C) color (D) shape (E) magnetic field
19. If the Sun is moved to 2 AU away from us, with everything else remaining the same, its luminosity
(A) is decreased by a factor of four, and the apparent brightness is decreased by a factor of four.
(B) is decreased by a factor of two, and the apparent brightness is decreased by a factor of two.
(C) remains the same, but the apparent brightness is decreased by a factor of two.
(D) remains the same, but the apparent brightness is decreased by a factor of four.
(E) is decreased by a factor of four, but the apparent brightness remains the same.
20. A white dwarf star has the same diameter as the Earth but its photosphere temperature is 100
times higher. How much larger is its luminosity compared that of the Earth?
(A) the same (B) 102 times (C) 104 times (D) 108 times (E) 1012 times
21. A star has a parallax of 1/4 seconds of arc. Its distance is therefore
(A) 0.5 parsecs. (B) 1 parsec. (C) 2 parsecs. (D) 4 parsecs. (E) 10 parsecs.
22. Stars begin to evolve off the main sequence when
(A) their core begins to burn helium into carbon.
(B) the hydrogen in their core is nearly used up.
(C) their cores become iron.
(D) their cores become uranium.
(E) they lose touch with reality.
23. A white dwarf star is
(A) burning hydrogen. (B) burning helium.
(D) burning uranium. (E) simply cooling off.
(C) burning iron.
24. What kind of pressure supports a white dwarf from its own weight?
(A) neutron degeneracy pressure (B) electron degeneracy pressure
(C) thermal pressure (D) radiation pressure (E) peer pressure
25. Near the photon sphere of a black hole, you may be able to see the back of your own head.
This describes
(A) Hawking radiation.
(B) the curvature of space caused by gravity of the black hole.
(C) that you need to get eyes checked out.
(D) the X-ray emission the black hole would emit.
(E) that a black hole is not made of dark matter.
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26. What powers the luminosity of a protostar?
(A) nuclear fusion
(B) radio activity
(C) degeneracy pressure
(D) a black hole
(E) gravitational potential energy
27. Why is a black hole “black”?
(A) Their light peaks in the black color.
(B) No light can escape, so it looks dark.
(C) It is really brown, and the name has nothing to do with color.
(D) It emits in all colors, and the mixture has the black color.
(E) A black hole is actually white.
28. What did Carl Sagan mean when he said that we are all “star stuff”?
(A) that life would be impossible without energy from the Sun.
(B) that Earth formed at the same time as the Sun.
(C) that the Universe contains billions of stars.
(D) that carbon, oxygen, and many elements essential to life were created in stellar cores.
(E) that the Sun formed from the interstellar medium: the “stuff” between the stars.
29. Why does the star’s core get hotter as the core shrinks?
(A) The fuels settle there to liberate their heat.
(B) The core is compressed and compression heats a gas.
(C) The core spins faster and friction heats it.
(D) The magnetic field in the core generates heat when compressed.
(E) The statement is false. A shrinking core cools.
30. Which of the following is the closest in mass to a white dwarf?
(A) Snow White (B) the Moon (C) the Earth (D) Jupiter
(E) the Sun
31. What happens when the gravity of a massive star is able to overcome 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 cannot overcome neutron degeneracy pressure.
32. Massive stars cannot generate energy through iron fusion because
(A) stars contain very little iron.
(B) no star can get hot enough for iron fusion.
(C) iron has the lowest mass per nuclear particle of all nuclei.
(D) massive stars go supernova before they create an iron core.
(E) iron turns into rust when mixed with oxygen.
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33. When a star becomes a red giant it becomes much brighter because it is
(A) moving closer to us.
(B) losing its outer envelope.
(C) fusing iron in its core.
(D) increasing in size.
(E) heavier than before.
34. Hydrostatic equilibrium in stars refers to the balance between
(A) gravity and thermal pressure.
(B) gravity and electricity.
(C) radiation and temperature.
(D) magnetic field and nuclear force.
(E) water and fire.
35. The processes by which most energy is transferred from the Sun’s core to the photosphere are
(A) radiation and neutrino emission
(B) neutrino emission and convection
(C) conduction and convection
(D) radiation and convection
(E) hyperspace and worm holes
36. Which of the following would weigh the most?
(A) a spoonful of gold
(B) a spoonful of white dwarf
(C) a spoonful of neutron star
(D) a spoonful of the Sun
(E) an ice cube
37. Planets and brown dwarfs are distinguished from genuine stars by
(A) X-ray heating.
(B) a larger diameter.
(C) presence of oceans of water.
(D) no fusion inside.
(E) difference in composition.
38. Which of the following methods has led to the largest number of discoveries of massive planets
orbiting nearby stars?
(A) detecting the gravitational effect by looking for the Doppler shifts in the star’s spectrum.
(B) detecting the light reflected by the planet.
(C) detecting the infrared light emitted by the planet.
(D) detecting the shift of the star’s position against the sky due to the planet’s gravitational pull.
(E) detecting a planet ejected from a binary star system.
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39. Which of the following spacetime diagram describes two guys sleeping at the back of the lecture
hall?
40. Pulsars are known to spin from a few times per second. What makes them spin so fast?
(A) exclusion principle
(B) high magnetic field
(C) conservation of mass
(D) conservation of angular momentum
(E) radio activity
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Part 2
NAME:
SPIRE ID:
Write your name and ID number first. Answer any four of the following five questions
to your best ability. If you answer all five, the best four scores will be counted.
41. (a) Draw an H-R diagram below and identify the axis.
(b) Draw and identify the regions occupied by the (1) main sequence, (2) red giants, and (3) white
dwarfs.
(c) Draw a new H-R diagram below. Draw the main sequence again and identify where the Sun
should be.
(d) Draw the evolutionary track of the proto-Sun, starting from the parent gas cloud where the
Sun was born.
(e) Draw the evolutionary track of the Sun, after it leaves the main sequence. Identify the key
stages on the plot.
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42. (a) A Sun-like star is seen circling an empty spot in the sky. If the semi-major axis of the orbit
is 1 AU with an orbital period of 36 days (0.1 year), what is the total mass of this system?
(b) This dark companion could be a dark white dwarf, dark neutron star, or a black hole. How
would the above calculation be used to argue that this dark source is indeed a black hole?
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