1. Thermal radiation from cold interstellar dust peaks in the:
a) UV.
b) X-ray.
c) optical.
d) gamma ray.
e) far-infrared.

2. What produces the strong 21 cm radio line seen from interstellar clouds?
a) atomic hydrogen.
b) ionized hydrogen.
c) molecular hydrogen.
d) carbon monoxide.
e) interstellar dust.

3. In the Horsehead Nebula, the dark feature that makes the shape of the horse's head is:
a) An interstellar cloud that is 99 percent interstellar dust by mass.
b) An interstellar cloud that is 75 percent hydrogen gas, 24 percent helium gas, by mass, and one percent dust and other chemical elements.
c) An interstellar cloud that is about half hydrogen and half dust by mass.
d) An interstellar cloud that is 99 percent carbon monoxide by mass.
e) An interstellar cloud that is 99 percent carbon by mass.

4. Where are HII regions located?
a) Around brown dwarfs.
b) Around GV stars.
c) Around AV stars.
d) Around OV stars.
e) Around red supergiant stars.

5. In what wavelength regime is the peak of the thermal spectrum of interstellar dust grains?
a) Infrared.
b) Optical.
c) X-ray.
d) Ultraviolet.
e) Gamma Rays.

6. Why do HII regions take on a reddish appearance in photographs?
a) Because of the hydrogen H-alpha line.
b) Because dust in the HII region preferentially scatters out blue light.
c) Because the temperature of the nebula is such that the peak of its thermal spectrum is in the red part of the spectrum.
d) They contain many very red stars, whose starlight dominates the light from the HII region.
e) They are very cold (about 100K), and therefore emit most of their light in the infrared, with just a little in the optical (mainly in the red part of the spectrum). Since photographic emulsion is not sensitive to infrared light, they appear red in photographs.

7. Eclipsing binaries are discovered by:
a) directly observing both stars.
b) observating the spectrum of the stars.
c) observation of a `wobble' in the position of the stars' positions with time.
d) periodic redshifting and blueshifting of the light from the planet's star.
e) observation of a periodic dimming of the combined light from the pair of stars.

8. Masses of stars can be measured by:
a) weighing them on a scale.
b) observing the motion of a single star as it moves through space.
c) monitoring the light curve of a variable star.
d) measuring the orbital period, Doppler shift, and separation of a visual binary.
e) wait for the star to pass near the Earth and send a spacecraft.

9. A brown dwarf is:
a) A very luminous star (10,000 solar luminosities) but very small star (0.1 solar radii).
b) A very luminous star (10,000 solar luminosities) with a temperature about 30,000K.
c) A low luminosity object (less than or equal to 0.01 solar luminosities) with a temperature about 30,000K.
d) A low mass object (less than 0.08 solar masses), with no nuclear fusion inside except perhaps deuterium fusion.
e) A white dwarf star.

10. Extrasolar planets:
a) is the generic name for the four largest planets: Jupiter, Saturn, Uranus, or Neptune.
b) are white dwarfs.
c) Can be found by observing their gravitational effect on their star or by searching for transits.
d) May exist, but have never been found.
e) Probably do not exist.

11. A planet orbiting a star in a circular orbit is:
a) not accelerating.
b) continually accelerating.
c) moving at a constant velocity.
d) not subject to an external force.
e) all of the above.

12. When two stars in a binary system are both clearly seen from Earth as individual stars, and their orbital motion can be measured to confirm that they are gravitationally bound together, the pair is called a/an:
a) Astrometric binary.
b) Visual binary.
c) Spectroscopic binary.
d) Optical double.
e) Eclipsing binary.

13. What happens to the observed color of a star when it is behind an interstellar cloud?
a) It appears bluer than it really is.
b) It appears redder than it really is.
c) Its color does not change; it gets dimmer the same amount at all wavelengths.
d) The optical color doesn't change, but all of the IR light from the star is absorbed by the cloud.
e) The red and blue light gets dimmed similar amounts, while the yellow light is not affected by the cloud.

14. The mass of an OV star is about:
a) 10⁴ solar masses.
b) 40 solar masses.
c) 2 solar masses.
d) 1 solar mass.
e) 0.1 solar masses.

15. Which of the following types of stars has the biggest mass?
a) M5V.
b) K3V.
c) G2V.
d) B3V.
e) O9V.

16. The interstellar medium is:
a) always very cold, about 10K.
b) about 99 percent hydrogen and helium.
c) about half gas, half dust.
d) about 99 percent dust, 1 percent gas.
e) completely ionized.

17. To detect cold neutral interstellar atomic clouds (i.e., HI clouds), the best method is to search for:
a) The red H-alpha line.
b) The blue/green H-beta line.
c) The 21 cm radio line of hydrogen.
d) the 2.6 millimeter line of carbon monoxide.
e) a diffuse reddish glow in an astronomical photograph.

18. The reddish glowing nebula that is visible around main sequence O stars is called a:
a) HI cloud.
b) HII region.
c) molecular cloud.
d) dark cloud.
e) reflection nebula.

19. What is the relationship between the mass and the luminosity of a main sequence star, approximately?
a) the luminosity is inversely proportional to the mass.
b) the luminosity is inversely proportional to the mass squared.
c) the luminosity is proportional to the mass.
d) the luminosity is proportional to the mass to the fourth power.
e) the luminosity does not depend upon mass; all main sequence stars have the same mass.

20. Which of the following techniques is NOT a viable method for detecting interstellar dust?
a) thermal radiation in the far-infrared from the dust grains.
b) thermal radiation in the optical from the dust grains.
c) scattered blue starlight from the dust grains.
d) absorption of optical light by the dust grains.
e) reddening of background stars due to intervening dust.

21. An HII region is a/an:
a) Ionized interstellar gas cloud seen around a main sequence O star.
b) Cold interstellar atomic hydrogen cloud.
c) Ionized interstellar gas cloud seen around the burned-out core of a star like the Sun.
d) Remnant of a supernova explosion.
e) Molecular cloud.

22. Which of the following objects is best described as a reflection nebula?
a) the red glowing cloud around the O stars in the Orion Nebula.
b) the horse's head in the Horsehead Nebula.
c) the glowing shell of gas and dust surrounding the core of a dying star.
d) the cloud of material left-over after a supernova explosion, for example, the Crab Nebula.
e) The glowing blue clouds seen around the stars in the Pleiades star cluster.

23. The 2.6 millimeter line of the carbon monoxide molecule is often used as a way to find:
a) HI clouds.
b) HII regions.
c) Supernova remnants.
d) Planetary Nebulae.
e) Molecular Clouds.

24. What information can be obtained if an extrasolar planet is observed transiting its star?
a) Whether or not it is inhabited.
b) Its temperature.
c) Its physical diameter.
d) Its distance from Earth.
e) All of the above.

25. What do Astronomers call an object with a mass between about 0.013 solar masses and 0.08 solar masses, that never became a star?
a) a white dwarf.
b) a brown dwarf.
c) a black dwarf.
d) a Jovian planet.
e) an extrasolar planet.

26. The H-alpha line of hydrogen:
a) is 21 cm in wavelength.
b) produces the blue glow seen around the stars in the Pleiades star cluster.
c) produces the red glow seen from hot ionized interstellar gas clouds.
d) is a very strong yellow line.
e) is extremely strong from molecular clouds.

27. Observationally, how can one distinguish a B star that lies behind an interstellar cloud from an unobscured G star?
a) from their Doppler shifts.
b) from their spectra.
c) from their B - V colors.
d) from their proper motions.
e) all of the above.

28. The very bright `glow' from interstellar clouds at about 100 microns, in the far-infrared, is due to:
a) the H-alpha line of hydrogen.
b) thermal emission from interstellar dust grains.
c) radiation from the spin-flip of electrons in the ground state of atomic hydrogen.
d) the combined light of many white dwarf stars.
e) the combined light of many extrasolar planets.

29. Which of the following is NOT a way to detect interstellar dust?
a) the 21 cm emission line.
b) the reddening of stars behind interstellar clouds.
c) the scattering of blue starlight.
d) thermal radiation in the far-infrared.
e) the absorption of the light from background stars in the optical.

30. A planetary nebula is:
a) An interstellar gas cloud in the process of creating a star and solar system.
b) The expanding outer layers of a dying star that are ionized by the hot core of the star.
c) A gas cloud created by the explosion of a massive star.
d) A dense molecular cloud.
e) A ionized gas cloud surrounding a main sequence O star.

31. An astrometric binary star pair is:
a) a pair of stars that are lined up such that one star passes directly in front of the other star, as seen from Earth.
b) a pair of stars that are too close together to resolve, but whose spectrum shows lines from two stars.
c) a pair of stars in which one star is too faint to see from Earth, but its existence can be inferred by the periodic wobble of its companion's position on the sky.
d) a widely separated pair of stars, which can both be clearly seen from Earth.
e) two stars that are not near each other in 3-dimensional space, but happen to be near each other on the sky.

32. A visual binary star is:
a) a pair of stars that are lined up such that one star passes directly in front of the other star, as seen from Earth.
b) a pair of stars that are too close together to resolve, but whose spectrum shows lines from two stars.
c) a pair of stars in which one star is too faint to see from Earth, but its existence can be inferred by the periodic wobble of its companion's position on the sky.
d) a widely separated pair of stars orbiting each other, which can both be seen from Earth.
e) two stars that are not near each other in 3-dimensional space, but happen to be near each other on the sky.

33. A planetary nebula is ionized by an object that is in the process of becoming a/an:
a) neutron star.
b) horizontal branch star.
c) white dwarf.
d) brown dwarf.
e) OV star.

34. Which of the following objects does NOT have a spectrum that peaks in the infrared?
a) an interstellar dust grain.
b) a protostar.
c) Betelgeuse.
d) a white dwarf.
e) a brown dwarf.

35. As an interstellar cloud gravitationally collapses, it spins faster due to the conservation of:
a) angular momentum.
b) linear momentum.
c) energy.
d) mass.
e) luminosity.

36. A planetary nebula is:
a) An ionized interstellar gas cloud seen around a main sequence O star.
b) A blue glowing cloud around a main sequence B star.
c) An ionized gas shell around the burned-out core of a star like the Sun.
d) A remnant of the explosion of a high mass star.
e) A flattened disk of dust and gas with a protostar in the core.

37. The red glowing emission seen throughout the Orion nebula is caused by:
a) starlight scattering off interstellar dust.
b) thermal radiation from interstellar dust.
c) radiation from the spin-flip of an electron in a hydrogen atom.
d) a very strong Doppler shift.
e) the strong red H-alpha emission line from hydrogen gas.

38. What is one way that molecular clouds are detected?
a) The 21 cm line of HI.
b) The H-alpha line from hydrogen.
c) The H-beta line from hydrogen.
d) The 2.6 millimeter line of CO.
e) No molecular clouds have been detected so far, although they are hypothesized to exist.

39. A brown dwarf is:
a) a very cold main sequence star.
b) the burned-out core of a star like the Sun.
c) a cooled-off white dwarf.
d) an object with too low mass to become a star.
e) an extrasolar planet.

40. From the bottom to the top of the main sequence, the luminosity of stars increases by a factor of about 10⁸. By what factor does the mass increase, approximately?
a) 400
b) 10⁷
c) 10¹⁴
d) 10
e) The masses of all main sequence stars are about the same.

41. The very strong emission line at 21 cm detected by radio telescopes is produced by:
a) neutral atomic hydrogen.
b) ionized hydrogen.
c) molecular hydrogen.
d) carbon monoxide.
e) interstellar dust.

42. On the H-R diagram, white dwarfs are located:
a) on the lower right.
b) on the lower left.
c) on the upper right.
d) on the upper left.
e) near the middle.

43. Which of the following objects does NOT have a spectrum that peaks in the infrared?
a) an interstellar dust grain.
b) a protostar.
c) Betelgeuse.
d) a white dwarf.
e) a brown dwarf.

44. The light curve of a star is a plot of what property of the star vs. time?
a) proper motion vs. time.
b) position vs. time.
c) velocity vs. time.
d) brightness vs. time.
e) angular size vs. time.

45. MV stars are:
a. the hottest known stars.
b. brown dwarfs.
c. very short-lived stars.
d. inert balls of carbon.
e. fusing hydrogen to helium in their cores.

46. An alpha particle is:
a) an ionized hydrogen atom.
b) a ²H nucleus.
c) a ⁴He nucleus.
d) a carbon-12 nucleus.
e) an ⁵⁶Fe nucleus.

47. What is another name for a helium-4 nucleus?
a) a positron.
b) a deuterium nucleus.
c) a beta particle.
d) an alpha particle.
e) a gamma particle.

48. When a one solar mass star has evolved to become an asymptotic giant branch star, which is moving up and to the right on the H-R diagram, what is its internal structure like?
a) An inert hydrogen core, surrounded by multiple layers of shell burning, with increasingly light chemical elements from silicon to hydrogen.
b) Core helium burning, surrounded by a shell of hydrogen burning.
c) An inert carbon core, surrounded by a shell of helium burning and a shell of hydrogen burning.
d) Hydrogen fusion in the core, surrounded by a shell of helium burning.
e) An iron core, surrounded by multiple layers of shell burning, with increasingly light chemical elements from silicon to hydrogen.

49. A planetary nebula is:
a) An interstellar gas cloud in the process of creating a star and solar system.
b) The expanding outer layers of a dying star that are ionized by the hot core of the star.
c) A gas cloud created by the explosion of a massive star.
d) A dense molecular cloud.
e) A ionized gas cloud surrounding a main sequence O star.

50. When a one solar mass star first leaves the main sequence, and starts moving through the subgiant (IV) portion of the H-R diagram, what is occuring inside the star?
a) helium fusion in the core, hydrogen fusion in a shell surrounding the core.
b) hydrogen fusion in the core, helium fusion in a shell surrounding the core.
c) no fusion in the core, hydrogen fusion in a shell surrounding the core.
d) no fusion in the core, helium fusion in a shell surrounding the core.
e) carbon fusion in the core, helium fusion in a shell surrounding the core.

51. Which of the following types of stars have main sequence lifetimes longer than the current age of the Universe?
a) 09V.
b) M5V.
c) A1V.
d) G2V.
e) B1V.

52. A star cluster is observed to have a full main sequence, from M stars to O stars. Approximately how old is this cluster?
a) Less than a few million years old.
b) 100 million years old.
c) 1 billion years old.
d) 10 billion years old.
e) 1 trillion years old.

53. Inspect the H-R diagram to the right. Stars that lie at position X:
a) have main sequence lifetimes of about trillion years.
b) have main sequence lifetimes of 10 billion years.
c) have main sequence lifetimes of 1 billion years.
d) have main sequence lifetimes of 1 million years.
e) live forever.

54. Which of the following statements is true about the lifetimes of main sequence stars?
a) Lower luminosity main sequence stars live longer than higher luminosity main sequence stars.
b) Main sequence A stars live longer than main sequence K stars.
c) Hot main sequence stars live longer than cool main sequence stars.
d) The greater the mass of a star, the longer its main sequence lifetime.
e) All main sequence A stars ever formed are still main sequence A stars.

55. What is the relationship between the mass and the luminosity of a main sequence star, approximately?
a) the luminosity is inversely proportional to the mass.
b) the luminosity is inversely proportional to the mass squared.
c) the luminosity is proportional to the mass.
d) the luminosity is proportional to the mass to the fourth power.
e) the luminosity does not depend upon mass; all main sequence stars have the same mass.

56. A star cluster is observed to have a main sequence that extends up to G stars, with no more luminous main sequence stars seen. Approximately how old is this cluster?
a) A few million years old.
b) 100 million years old.
c) 1 billion years old.
d) 10 billion years old.
e) 1 trillion years old.

57. Interstellar dust:
a) Absorbs UV and optical light.
b) Emits infrared light.
c) Scatters UV and optical light.
d) Makes background stars appear redder than they really are.
e) All of the above.

58. In what wavelength regime is the peak of the thermal spectrum of interstellar dust grains?
a) Infrared.
b) Optical.
c) X-ray.
d) Ultraviolet.
e) Gamma Rays.

59. Which of the following statements is true about the lifetimes of main sequence stars?
a) Lower luminosity main sequence stars live longer than higher luminosity main sequence stars.
b) Main sequence A stars live longer than main sequence K stars.
c) Hot main sequence stars live longer than cool main sequence stars.
d) The greater the mass of a star, the longer its main sequence lifetime.
e) All main sequence A stars ever formed are still main sequence A stars.

60. The age of a star cluster is equal to:
a) The main sequence lifetime of the lowest mass star in the cluster.
b) The main sequence lifetime of the star at the top of the observed main sequence in the H-R diagram of the star cluster.
c) All star clusters in the Milky Way formed about 10 billion years ago.
d) All star clusters in the Milky Way formed about 1 million years ago.
e) All star clusters in the Milky Way are 13.7 billion years old.

61. The angular momentum of a spinning object is proportional to its:
a) mass X radius.
b) mass X spin velocity.
c) mass X spin velocity X radius.
d) mass X spin velocity X radius².
e) mass X spin velocity² X radius.

62. A protostar:
a) is extremely hot (about 30,000K).
b) is spinning more slowly than the interstellar cloud it formed from.
c) emits large quantities of ultraviolet radiation.
d) emits large quantities of X-ray radiation.
e) has a spectrum that peaks in the infrared regime.

63. The linear momentum of an object moving in a straight line is proportional to its:
a) mass X radius.
b) mass X velocity.
c) mass X velocity X radius.
d) mass X velocity X radius².
e) mass X velocity².

64. Approximately how long does it take before the hydrogen runs out in the core of a G2V star?
a) 3 million years.
b) 10 million years.
c) 10 billion years.
d) a trillion years.
e) a hundred trillion years.

65. Which of the following techniques is NOT a viable method for detecting interstellar dust?
a) thermal radiation in the far-infrared from the dust grains.
b) thermal radiation in the optical from the dust grains.
c) scattered blue starlight from the dust grains.
d) absorption of optical light by the dust grains.
e) reddening of background stars due to intervening dust.

66. Which of the following objects is best described as a reflection nebula?
a) the red glowing cloud around the O stars in the Orion Nebula.
b) the horse's head in the Horsehead Nebula.
c) the glowing shell of gas and dust surrounding the core of a dying star.
d) the cloud of material left-over after a supernova explosion, for example, the Crab Nebula.
e) The glowing blue clouds seen around the stars in the Pleiades star cluster.

67. Observationally, how can one distinguish a B star that lies behind an interstellar cloud from an unobscured G star?
a) from their Doppler shifts.
b) from their spectra.
c) from their B - V colors.
d) from their proper motions.
e) all of the above.

68. The very bright `glow' from interstellar clouds at about 100 microns, in the far-infrared, is due to:
a) the H-alpha line of hydrogen.
b) thermal emission from interstellar dust grains.
c) radiation from the spin-flip of electrons in the ground state of atomic hydrogen.
d) the combined light of many white dwarf stars.
e) the combined light of many extrasolar planets.

69. A planetary nebula is:
a) An interstellar gas cloud in the process of creating a star and solar system.
b) The expanding outer layers of a dying star that are ionized by the hot core of the star.
c) A gas cloud created by the explosion of a massive star.
d) A dense molecular cloud.
e) A ionized gas cloud surrounding a main sequence O star.

70. The Orion Nebula is an HII region, while the Pleiades contains reflection nebulae and the Hyades shows little nebulosity (extended diffuse emission) in the visible part of the spectrum. Therefore, the correct order in terms of age, from youngest to oldest, for these three star clusters is:
a) Orion, Hyades, Pleiades.
b) Hyades, Pleiades, Orion.
c) Orion, Pleiades, Hyades.
d) Pleiades, Orion, Hyades.
e) Hyades, Orion, Pleiades.

71. The most massive stars are how many times more massive than the lowest mass stars, approximately?
a) 400 times.
b) 10⁸ times.
c) 10 times.
d) 1.5 times.
e) 10⁶ times.

72. What kind of interstellar clouds are the densest?
a) Ionized clouds.
b) HI clouds.
c) Planetary Nebulae.
d) Molecular clouds.
e) HII regions.

73. Planetary nebulae are :
a) Ionized clouds.
b) Dark clouds.
c) Molecular clouds.
d) Interstellar dust, with just 1 percent of their mass in gas.
e) About half atomic gas and half molecular gas.

74. A brown dwarf is:
a) An extrasolar planet.
b) The burned-out core of a star like the Sun.
c) An MV star.
d) An MI star.
e) too low mass to have ¹H fusion in its core.

75. Which of the following produces strong continuum emission in the far-infrared, and dominates the light from the Milky Way galaxy in the far-infrared?
a) The spin-flip transition of atomic hydrogen.
b) Interstellar dust.
c) White dwarfs.
d) O, B, and A stars.
e) The H-alpha line from hydrogen atoms.

76. Planetary nebulae are:
a) Protostars.
b) The relics of past supernovae.
c) Ionized gas clouds around main sequence O stars.
d) The end stage of evolution of a 1 solar mass star.
e) Chunks of rock in our inner solar system, left-over from the early days of the solar system.

77. The interstellar medium is:
a) About half dust and half gas.
b) About half hydrogen and helium, with the other half being heavier elements.
c) About 99 percent gas, 1 percent dust.
d) All very hot, at least 10,000 K.
e) All very cold, less than 20K.

78. Which of the following types of stars has the lowest mass?
a) M5V.
b) K3V.
c) G2V.
d) B3V.
e) O9V.

79. The strong 21 cm line detected by radio telescopes is due to:
a) very cold interstellar dust.
b) the spin-flip of the electron in hydrogen atoms.
c) carbon monoxide molecules.
d) signals from extraterrestrial civilizations on extrasolar planets.
e) molecular hydrogen.

80. A planetary transit is when:
a) A planet in our solar system travels the full distance across the sky from the eastern horizon to the western horizon.
b) A planet in our own solar system makes a full orbit around the Sun, relative to the stars.
c) A planet travels across the face of its star, as seen by an observer on Earth.
d) An extrasolar planet makes a full orbit around its star, as indicated by Doppler shift measurements.
e) The position of an extrasolar planet's star makes a complete `wobble' in the plane of the sky, indicating a full orbit.

81. As an interstellar cloud gravitationally collapses in the process of forming a star:
a) it spins more and more slowly.
b) the spin velocity remains constant.
c) the core gets colder and colder.
d) the temperature of the core remains the same.
e) none of the above.

82. Comparing main sequence A stars with main sequence M stars:
a) Main sequence A stars have shorter main sequence lifetimes.
b) Main sequence A stars are red, while M stars are blue.
c) Main sequence A stars have lower stellar masses.
d) Main sequence A stars are lower luminosity.
e) All of the above.

83. What is the approximate main sequence lifetime of an O star?
a) five hundred trillion years.
b) About 10 trillion years.
c) About a trillion years.
d) About 10 billion years.
e) A few million years.

84. Most of the thermal emission (blackbody radiation) from interstellar dust grains is in the:
a) X-ray.
b) ultraviolet.
c) visible.
d) gamma ray.
e) infrared.

85. The Pleiades star cluster contains many main sequence B stars, but no O stars. In contrast, the NGC 6705 cluster contains both O and B stars, and the Praesepe cluster contains neither. The relative ages of the three clusters is therefore (from youngest to oldest):
a) Pleiades; NGC 6705; Praesepe.
b) NGC 6705; Pleiades; Praesepe.
c) Praesepe; Pleiades; NGC 6705.
d) It is impossible to tell the relative ages of the three clusters with the given information.
e) All three clusters are the same age.

86. Main sequence B stars, like those in the Pleiades, are often surrounded by blue glowing nebulae. What produces these nebulae?
a) Emission lines from interstellar hydrogen gas.
b) Blackbody radiation from very hot (30,000K) dust surrounding the star.
c) Preferential reflection of blue starlight by interstellar dust.
d) Ionization of the surrounding gas cloud by ultraviolet photons from the star.
e) Gravitational contraction of an interstellar cloud surrounding the star.

87. Millimeter (microwave) telescopes detect the 2.6 millimeter emission lines from dense interstellar gas clouds. What produces this line?
a) Atomic hydrogen gas.
b) Molecular hydrogen.
c) Carbon monoxide.
d) interstellar dust.
e) Ionized helium.

88. What luminosity class stars approximately obey the mass-luminosity relation described by the formula luminosity is proportional to mass to the fourth power?
a) I.
b) II.
c) III.
d) IV.
e) V.

89. What is the mass, approximately, of a main sequence M star?
a) 40 solar masses.
b) 10 solar masses.
c) 5 solar masses.
d) 1 solar mass.
e) 0.1 solar mass.

90. The highest luminosity stars are how many times more luminous than the lowest luminosity stars, approximately?
a) 400 times.
b) 10⁸ times.
c) 10 times.
d) 1.5 times.
e) 10,000 times.

91. Atomic interstellar clouds can be most easily detected using:
a) the 21 cm emission line of hydrogen.
b) the red H-alpha emission line of hydrogen.
c) the 2.6 mm emission line of carbon monoxide.
d) Ultraviolet emission lines from hydrogen.
e) atomic clouds have not yet been detected, but are hypothesized to exist.

92. As it is in the process of dying, a one solar mass main sequence star like our Sun will become a/an:
a) brown dwarf.
b) supernovae remnant.
c) planetary nebula.
d) HII region.
e) extrasolar planet.

93. The mass of our Sun is:
a) larger that that of M2V and K2V stars, and smaller than that of B0V stars.
b) smaller that that of M2V and K2V stars, and larger than that of B0V stars.
c) larger that that of B0V stars, and smaller than that of M2V and K2V stars.
d) larger that that of M2V stars, and smaller than that of B0V and K2V stars.
e) smaller that that of M2V stars, and larger than that of B0V and K2V stars.

94. What is the Astronomical term used when a planet is traveling across the face of its star as seen from Earth (i.e., when a planet orbiting another star is passing between us and that star)?
a) sailing.
b) scoping.
c) spotting.
d) transiting.
e) exoing.

95. A spectroscopic binary star is:
a) a pair of stars that are lined up such that one star passes directly in front of the other star, as seen from Earth.
b) a pair of stars that are too close together to resolve, but whose spectral lines indicates the presence of two stars.
c) a pair of stars in which one star is too faint to see from Earth, but its existence can be inferred by the periodic wobble of its companion's position on the sky.
d) a widely separated pair of stars orbiting each other, which can both be seen individually from Earth.
e) two stars that are not near each other in 3-dimensional space, but happen to be near each other on the sky.

96. What type of stars have main sequence lifetimes of about 10 billion years?
a) M2V.
b) O9V.
c) B2V.
d) G2V.
e) A0V.

97. The far-infrared (long wavelength infrared) light from the Milky Way galaxy as a whole is dominated by emission from:
a) the photospheres of hot stars like Vega and Rigel.
b) the photospheres of cold stars like Betelgeuse.
c) the photospheres of moderate-temperature stars like the Sun.
d) cold interstellar dust grains.
e) the H-alpha emission line of hydrogen.

98. The spin-flip spectral line of hydrogen:
a) is 21 cm in wavelength.
b) produces the blue glow seen around the stars in the Pleiades star cluster.
c) produces the red glow seen from hot ionized interstellar gas clouds.
d) is a very strong yellow line.
e) is strongest from molecular clouds.

99. Blue reflection nebulae are more likely to be observed around what kind of stars?
a) G stars.
b) M stars.
c) B stars.
d) F stars.
e) K stars.

100. The main reaction going on now in the core of the Sun is the proton-proton chain. Later in its life, the triple alpha reaction will start in its core. What is the end product of the triple alpha reaction?
a) helium-3.
b) helium-4.
c) carbon-12.
d) carbon-14.
e) deuterium.

101. The formal name of a plot of the brightness of a star vs. time is:
a) Doppler curve.
b) Binary curve.
c) Exo curve.
d) Light curve.
e) Astrometric curve.

102. In class, we did a demonstration in which a person sat on a stool and spun around. When he pulled in his arms, he spun faster. The reason this happens is because of:
a) mass conservation.
b) energy conservation.
c) linear momentum conservation.
d) angular momentum conservation.
e) the center of mass relation.

103. What is one difference between a planet like Jupiter and a brown dwarf?
a) there is no difference: Jupiter is an example of a brown dwarf.
b) a brown dwarf is the burned-out core of a star that has run out of nuclear fuel.
c) a brown dwarf is a low luminosity main sequence star.
d) a brown dwarf may have ¹H fusion going on in its core; Jupiter does not.
e) a brown dwarf may have ²H fusion going on in its core; Jupiter does not.

104. If a binary pair of stars is observed as both an eclipsing binary star and as a double-lined spectroscopic binary, one can measure the Doppler shifts of the stars and also time the eclipses. From this information, one can directly determine:
a) the distance to the stars.
b) the radii of the stars.
c) the proper motion of the stars.
d) the age of the stars.
e) none of the above.

105. The most massive main sequence stars are approximately:
a) 2 solar masses.
b) 3 solar masses.
c) 40 solar masses.
d) 4000 solar masses.
e) 4 X 10⁶ solar masses.

106. What is the approximate dividing line in mass between a brown dwarf and a normal star (i.e., a star with ¹H fusion)?
a) 0.8 solar masses.
b) 0.5 solar masses.
c) 0.08 solar masses.
d) 0.0001 solar masses.
e) 10^-6 solar masses.

107. What kind of interstellar clouds are found around main sequence O stars?
a) Ionized clouds.
b) HI clouds.
c) Molecular clouds.
d) Dark clouds.
e) It depends upon the luminosity class of the star.

108. An alpha particle is:
a) A neutron.
b) A proton.
c) An anti-electron.
d) An anti-proton.
e) A helium-4 nucleus.

109. The most luminous main sequence stars are approximately:
a) 10 solar luminosities.
b) 100 solar luminosities.
c) 10,000 solar luminosities.
d) a million solar luminosities.
e) 10⁹ solar luminosities.

110. The glowing blue clouds around the stars in the Pleiades star clusters are caused by:
a) the spin-flip transition of hydrogen.
b) the H-alpha emission line of hydrogen.
c) the H-beta emission line of hydrogen.
d) blue starlight being scattered from interstellar dust grains.
e) emission lines from carbon monoxide molecules.

111. If a star cluster contains main sequence O stars:
a) It must be about 10 billion years old.
b) It must be about 10 trillion years old.
c) It must be less than a few million years old.
d) It must be about a billion years old.
e) It must be a globular cluster.

112. The mass of a B2V star is:
a) larger that that of M2V and K2V stars, and smaller than that of G2V stars.
b) larger that that of M2V stars, and smaller than that of K2V and G2V stars.
c) smaller that that of M2V stars, and larger than that of K2V and G2V stars.
d) smaller that that of M2V, K2V, and G2V stars.
e) larger that that of M2V, K2V, and G2V stars.

113. The white dwarf star Sirius B was initially discovered because:
a) it eclipses Sirius A, periodically blocking part of the light.
b) it is about the same brightness as Sirius A, and both can clearly be seen together in the sky without a telescope.
c) Astronomers watched it form.
d) It is colder than Sirius A, and the peak of its spectrum is in the infrared.
e) it causes the position of Sirius A to `wobble' in the sky.

114. In the demonstration done in class with the spinning stool, what happened when the spinning person on the stool pulled in his arms?
a) he fell over.
b) his spin rate decreased.
c) his spin rate didn't change.
d) his spin rate increased.
e) he stopped spinning.

115. What fraction of the mass of the interstellar medium is dust?
a) 1 percent.
b) 10 percent.
c) 50 percent.
d) 90 percent.
e) 99 percent.

116. When a 1 solar mass star leaves the main sequence, what luminosity class star does it become first, immediately after leaving the main sequence?
a) I.
b) II.
c) III.
d) IV.
e) V.

117. If an interstellar cloud sits between us and a background star, what happens to the appearance of the star (compared to a star not behind a cloud)?
a) the star will appear bluer than it otherwise would.
b) the star will appear redder than it otherwise would.
c) the color of the star will not change, but it will appear fainter at all wavelengths.
d) the star will be fainter in yellow and green, but brighter in blue and red.
e) the star will not be detected at all in red light, but will be the same brightness in blue.

118. The ground state of an electron in a hydrogen atom is split into two levels, because of the spin of the electrons. When an electron "flips its spin" and jumps between these two levels, what kind of a photon is produced?
a) 21 cm.
b) H-alpha.
c) H-beta.
d) 2.6 mm.
e) an X-ray photon.

119. The most massive stars in the Orion Nebula are:
a) G stars.
b) M stars.
c) B stars.
d) F stars.
e) O stars.

120. Which nuclear reaction or reactions inside 1 solar mass stars is the dominant process that produces carbon-12 atoms?
a) the proton-proton chain.
b) the triple alpha process.
c) ¹⁴N losing a deuterium nucleus.
d) two lithium-6 atoms fusing together.
e) a boron-11 nucleus fusing with ¹H.

121. In Astronomy, the term "Light Curve" refers to:
a) A plot of frequency vs. brightness.
b) A plot of wavelength vs. brightness.
c) A plot of the velocity of a star vs. time.
d) A plot of the position of a star on the sky vs. time.
e) A plot of the brightness of a star vs. time.

122. Which of the following is true about Asymptotic Giant Branch stars?
a) They are sometimes pulsating variable stars.
b) They lie below the main sequence on an H-R diagram.
c) They are protostars.
d) They are luminosity class V stars.
e) They are brown dwarf stars.

123. What do Astronomers call the burnt-out core of a star like the Sun, after it has ended its nuclear reactions and has lost its outer layers?
a) a white dwarf.
b) a brown dwarf.
c) a black hole.
d) a red dwarf.
e) an extrasolar planet.

124. Which of the following is NOT a valid method of measuring the radii of some stars?
a) measure their luminosities and temperatures.
b) measure their proper motions.
c) if it is in an eclipsing binary, time how long an eclipse lasts.
d) measure their angular sizes.
e) none of the above methods work for any stars; we are not able to determine the radii of any stars by any method.

125. Which of the following statements is NOT true about the lifetimes of main sequence stars?
a) Lower luminosity main sequence stars live longer than higher luminosity main sequence stars.
b) Main sequence G stars live longer than main sequence A stars.
c) Hot main sequence stars live longer than cool main sequence stars.
d) Main sequence B stars live longer than main sequence O stars.
e) All main sequence M stars ever formed are still main sequence M stars.

126. What is a planetary nebula?
a) A ionized gas cloud surrounding a main sequence O star.
b) A protostar.
c) The expanding outer layers of a dying star that are ionized by the hot core of the star.
d) The remnant of a supernova explosion.
e) A brown dwarf.

127. The extended red emission seen behind the Horsehead Nebula in optical photographs is caused by:
a) the H-alpha emission line of hydrogen.
b) emission from cold interstellar dust in the red part of the spectrum.
c) blackbody radiation from cold interstellar molecular hydrogen.
d) emission lines from carbon gas in the interstellar medium.
e) the Doppler shift.

Answers: 1e, 2a, 3b, 4d, 5a, 6a, 7e, 8d, 9d, 10c, 11b, 12b, 13b, 14b, 15e, 16b, 17c, 18b, 19d, 20b, 21a, 22e, 23e, 24c, 25b, 26c, 27b, 28b, 29a, 30b, 31c, 32d, 33c, 34d, 35a, 36c, 37 e, 38d, 39d, 40a, 41a, 42b, 43d, 44d, 45e, 46c, 47d, 48c, 49b, 50c, 51b, 52a, 53b, 54a, 55d, 55d, 57e, 58a, 59a, 60b, 61c, 62e, 63b, 64c, 65b, 66e, 67b, 68b, 69b, 70c, 71a, 72d, 73a, 74e, 75b, 76d, 77c, 78a, 79b, 80c, 81e, 82a, 83e, 84e, 85b, 86c, 87c, 88e, 89e, 90b, 91a, 92c, 93a, 94d, 95b, 96d, 97d, 98a, 99c, 100c, 101d, 102d, 103e, 104b, 105c, 106c, 107a, 108e, 109c, 110d, 111c, 112e, 113e, 114d, 115a, 116d, 117b, 118a, 119e, 120b, 121e, 122a, 123a, 124b, 125c, 126c, 127a.