1 Astronomy 101.002 Hour Exam 3 April 13, 2009 Answers Given in BOLD FACE QUESTION 1: The Sun produces energy by what kind of reaction? a) Burning (a chemical reaction). b) Fusion. c) Fission. d) Dark energy. e) Magnetohydrodynamics. QUESTION 2: A fusion reaction results in: a) The building up of heavier nuclei from light nuclei. b) The breaking apart of heavy nuclei into lighter ones. c) The annihilation of nuclei. d) The annihilation of antimatter. e) Carbon dioxide. QUESTION 3: The most tightly bound nucleus is: a) Hydrogen. b) Helium. c) Carbon. d) Iron. e) Uranium. QUESTION 4: Fusion reactions release energy by: a) Converting mass into energy. b) Reducing nuclear binding energies. c) Creating simpler forms of matter. d) Producing neutrinos. e) The weak nuclear force. QUESTION 5: The present level of the production of energy on the Sun results in a) The Sun getting less massive. b) The Sun getting more massive. c) The Sun getting hotter. d) The Sun getting cooler. e) The Sun rotating faster. QUESTION 6: Fusion occurs only near the Sun’s center because: a) Only near the center is there enough hydrogen that is not mixed with other elements. b) Only near the center is the helioseismology favorable for fusion. c) Heat is transferred down to the center to ignite fusion. d) Only at the center are the temperature and pressure high enough to sustain fusion. e) The statement is false: fusion occurs throughout the Sun. 2 QUESTION 7: The mass of a star can be determined by: a) Measuring its luminosity b) Determining its composition. c) Measuring its color. d) Measuring its Doppler shift. e) Studying its orbit around a binary companion. QUESTION 8: Cool stars can be very luminous if they are: a) Small. b) Hot. c) Large. d) Close to our solar system. e) In a binary system. QUESTION 9: The color of a star is most directly related to its: a) Mass. b) Surface temperature. c) Core temperature. d) Luminosity. e) Density. QUESTION 10: Which of the following properties of stars can be determined without knowing the star-Earth distance? a) Luminosity. b) Density. c) Radius. d) Rotation period. e) Surface temperature. QUESTION 11: If the star α-Cygni were twice as far away as it actually is, its absolute luminosity would change by what factor? a) Double. b) Four times. c) One-half. d) One-quarter. e) Unchanged. QUESTION 12: If two stars have the same radius but different temperatures, then the hotter star will be: a) Bluer and brighter. b) Redder and brighter. c) Bluer and fainter. d) Redder and fainter. e) Redder but the same brightness. QUESTION 13: The difference between a star’s absolute magnitude and apparent magnitude is a measure of its: a) Distance. b) Temperature. c) Luminosity. d) Mass. e) Color. 3 QUESTION 14: If two stars are observed with the same apparent brightness and are not obscured by dust or gas, then a) They have the same temperature. b) They are the same distance from us. c) They have the same angular size. d) The further one must have a greater luminosity. e) They have the same luminosity. QUESTION 15: The region of the H-R diagram occupied by the most stars is the: a) Main sequence region. b) White dwarf region. c) Red giant region. d) Hot star region. e) Cool star region. QUESTION 16: Astronomers construct a Hertzsprung-Russell diagram from observed stars by plotting: a) Apparent brightness and distance. b) Distance and color. c) Size and surface temperature. d) Luminosity and distance. e) Luminosity and surface temperature. QUESTION 17: The visual magnitude of star, by itself, is a good indicator of: a) Its actual brightness. b) Its surface temperature. c) Its distance. d) Its size. e) Nothing. QUESTION 18: Star A appears blue and star B appears red. What do we know for sure? a) Star A is hotter than star B. b) Star A is cooler than star B. c) Star A is more luminous than star B. d) Star A is less luminous than star B. e) Star A is larger than star B. QUESTION 19: We know that giant stars are larger in diameter than main sequence stars even though we cannot directly measure their size because: a) They are more luminous for the same temperature. b) They are less luminous for the same temperature. c) They are hotter for the same luminosity. d) They are brighter for the same luminosity. e) They are more distant for the same luminosity. QUESTION 20: The physical property that most uniquely determines where a star will be on the main sequence is its a) Age. b) Distance. c) Mass. d) Size. e) Relative hydrogen abundance. 4 QUESTION 21: The coolest main-sequence stars have a surface temperature of approximately: a) 300 K. b) 3000 K. c) 6000 K. d) 10,000 K. e) Absolute zero. QUESTION 22: A pulsar is a) A binary star system containing a white dwarf. b) A rotating white dwarf. c) A rotating black hole. d) A rotating red giant star. e) A rotating neutron star. QUESTION 23: Two stars are each observed in January and again in July. Star A has a parallax of 1.03”, while the Star B has a parallax of 1.70”. What can you conclude? a) Star A is brighter than Star B. b) Star A is hotter than Star B. c) Star A is more massive than Star B. d) Star A is closer to earth than Star B. e) Star B is closer to earth than Star A. QUESTION 24: Sirius, the “dog star”, is a distance of ~2.5 pc from Earth. What can you conclude from this information? a) Sirius has a higher luminosity than the Sun. b) Sirius appears brighter than the Sun. c) Sirius has an observed parallax of 2.5”. d) Sirius has an observed parallax of 0.4”. e) The parallax of Sirius is too small to be measured. QUESTION 25: Sirius has an apparent magnitude of -1.5 and the Sun has an apparent magnitude of -26.7. What can you conclude from this information? a) The Sun appears brighter than Sirius. b) Sirius appears brighter than the Sun. c) Sirius is hotter than the Sun. d) The Sun is hotter than Sirius. e) Sirius is more luminous than the Sun. QUESTION 26: In order for a dark cloud to collapse it must: a) Not be spinning. b) Contain no molecules. c) Be very hot. d) Have a high internal pressure compared with its gravity. e) Have a low internal pressure compared with its gravity. QUESTION 27: The component of the Milky Way Galaxy that prevents us from seeing its center is: a) Hot hydrogen gas. b) Cold hydrogen gas. c) A dense concentration of stars. d) Interstellar dust. e) Intergalactic nebulae. 5 QUESTION 28: Interstellar dust can be recognized by its: a) Emission of 21-centimeter radiation. b) Absorption lines. c) Absorption of radio waves. d) Bright colors e) Blocking of starlight. QUESTION 29: If Star A has a radius twice as large as that of Star B, and the surface of Star B is twice as hot as Star A, which of the following must be true? a) Star A has a higher luminosity. b) Star B has a higher luminosity. c) The stars have the same luminosity. d) The stars have the same visual magnitude. e) None of the above. QUESTION 30: The interstellar medium is composed mostly of: a) Hydrogen and helium b) Hydrogen and oxygen. c) Nitrogen and oxygen. d) Metallic hydrogen. e) Dust. QUESTION 31: Given the following apparent magnitudes, which star looks the brightest? a) Alcyone – magnitude 2.86. b) Atlas – magnitude 3.62. c) Electra – magnitude 3.7. d) Maia – magnitude 3.86. e) Sterope – magnitude 5.64. QUESTION 32: Evidence for interstellar material is: a) The motion of stars slows down over time. b) Distant stars have large Doppler red shifts. c) Distant stars appear reddened. d) Most apparently bright stars are far from us. e) There is no way to detect the interstellar medium. QUESTION 33: The speed necessary to escape a black hole is: a) Infinite. b) Undefinable. c) Greater than or equal to the velocity of light. d) Less that but almost equal to the velocity of light. e) Greater than or equal to the velocity of sound. QUESTION 34: If two stars are the same size, which of the following must be true? a) The hotter star appears to be brighter. b) The hotter star appears to be bluer. c) The hotter star appears to be redder. d) The closer star appears to be brighter. e) The closer star appears to be bluer. QUESTION 35: In general relativity, gravity results in: a) Curved time. b) Curved space. c) Nuclear fusion. d) The strong nuclear force. e) The equivalence principle. 6 QUESTION 36: The main energy source in the star Aldebaran, a red giant, is which process? a) Nuclear fusion. b) Nuclear fission. c) Gravitational collapse. d) Combustion of hydrogen. e) A red giant does not produce any energy. QUESTION 37: A star on the main sequence maintains its size for a long time because of: a) Equilibrium between its degenerate electron pressure and its convection. b) Equilibrium between its energy generated by fusion and its luminosity. c) Equilibrium between its radiation pressure and convection. d) Equilibrium between its outward pressure and gravity. e) The statement is false – the star is constantly getting smaller. QUESTION 38: The most massive stars are believed to end up as: a) Pulsars.