Test Bank Characterizing Stars Chapter.12 14th Edition - Discovering the Universe 14e Test Bank + Answers by Neil F. Comins. DOCX document preview.
Chapter 12: Characterizing Stars
Section: Introduction
1. Which of these statements BEST characterizes the human study of stellar evolution?
A) The changes in the observable cosmos over a human lifetime are profound.
B) A human lifetime is long enough to witness the evolution of a star through much of its evolutionary history.
C) Astronomers have never witnessed a significant change in any single star.
D) At any moment. Stars can be observed in every phase of evolution.
Section: 12-1
2. The Sun is about 8000 parsecs from the center of the Milky Way Galaxy, while the Hipparcos satellite measured parallaxes to an accuracy of about 0.01 arcseconds. How far toward the galactic center could astronomers see with Hipparcos (ignoring galactic dust and other obstacles)?
A) all the way to the center
B) about halfway to the center
C) about 1/80 of the way to the center
D) about 1/1000 of the way to the center
3. How far away is the nearest star beyond the Sun?
A) about 1/4 ly away
B) about 1/10 ly away
C) about 4 ly away
D) between 1 and 2 ly away
4. How far away is the nearest star beyond the Sun, in parsecs?
A) between 1 and 2 pc
B) about 12 pc
C) about 4 pc
D) between 1/2 and 1 pc
5. What is parallax?
A) distance to an object, measured in parsecs
B) angle taken up by the size (e.g., diameter) of an object, as seen by an observer
C) shift in angular position of an object as it moves in space
D) apparent shift in position of an object as the observer moves
6. The first accurate measurement of stellar parallax was made in
A) the fourth century B.C.
B) 1721.
C) 1838.
D) 1927.
7. In what fundamental way do humans (and many other animals) utilize parallax for the measurement of distance?
A) The eyes focus back and forth continuously, and the brain interprets the focusing in terms of distance to the object viewed.
B) The eye can measure the time taken for light to travel from an object, and the brain interprets this information in terms of distance to the object viewed.
C) Humans are always moving their heads slightly from side to side, and the brain compares the angles from each of these positions to obtain the distance to the object viewed.
D) Human eyes are mounted horizontally about 10 cm apart, and the brain interprets the relative look angles of their eyes in terms of distance to the object viewed.
8. Stellar parallax is the
A) inferred change in the distance to a star as its light is dimmed by passing through an interstellar cloud.
B) apparent shift seen in the position of a nearby star against more distant stars as Earth orbits the Sun.
C) difference between the apparent and absolute magnitudes of a star.
D) circular or elliptical motion of a star in a binary system as the two stars orbit each other.
9. As a person drives along a road, trees in the middle distance seem to shift in position relative to faraway hills. What name is given to this phenomenon?
A) parallax
B) perspective
C) Doppler effect
D) inverse-square law
10. The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the
A) motion of the Sun around the galactic center.
B) change in latitude of the observation point on Earth.
C) motion of Earth in its orbit around the Sun.
D) rotation of Earth on its axis.
11. How many stars (other than the Sun) have an angle of parallax greater than 1 second of arc?
A) about a hundred
B) Millions
C) None
D) only one
12. Which of these statements can be used to define stellar parallax?
A) Stellar parallax is the angle taken up by the diameter of a star as seen from Earth.
B) Stellar parallax is the angle subtended by the radius of Earth’s orbit as seen from the star.
C) Stellar parallax is the angle subtended by the diameter of Earth’s orbit as seen from the star.
D) Stellar parallax is the angle through which a star moves in the sky over the course of 1 year due to the motion of both the star and Earth.
13. Parallax of a nearby star is used to estimate its
A) surface temperature.
B) distance from Earth.
C) apparent magnitude.
D) physical size or diameter.
14. Which of these properties of a nearby star is determined by a measurement of stellar parallax?
A) spectral type and surface temperature
B) rotation period
C) apparent magnitude
D) distance from Earth
15. The MOST straightforward way to determine the distance to a nearby star involves the measurement of the
A) star’s spectrum.
B) ratio of the star’s apparent and absolute magnitudes.
C) Zeeman effect of spectral lines in the star’s spectrum.
D) star’s parallax.
16. How can astronomers tell that some stars are relatively close to Earth?
A) The stars appear to move periodically back and forth against the background stars because of Earth’s movement around the Sun.
B) The stars appear to be extremely bright and must therefore be very close to Earth.
C) The stars are occasionally occulted or eclipsed by the Moon; hence they must be close.
D) The light from these stars shows only a very small redshift caused by the universal expansion of the universe, so they must be close.
17. Stellar parallax appears because
A) Earth rotates about its own axis.
B) stars move in space.
C) stars have finite size (i.e., they are not really just points of light).
D) Earth moves in space.
18. Aristotle (fourth century B.C.) rejected the idea that Earth moves because he knew stellar parallax motion would result, and he was unable to measure any. About how long after Aristotle was stellar parallax actually measured?
A) two centuries
B) 10 centuries
C) 22 centuries
D) 29 centuries
19. Who was the first person to measure the parallax of a star successfully?
A) Sir George Airy in England
B) Henry Norris Russell in the United States
C) Tycho Brahe in Denmark
D) Friedrich Wilhelm Bessel in Germany
20. The MOST accurate stellar parallax measurements for distances to the majority of stars in Earth’s neighborhood in the universe have been made by
A) the Hubble Space Telescope.
B) Friedrich Wilhelm Bessel, in 1838; no measurements since then have matched the precision of his measurements.
C) the Gaia satellite.
D) the Very Long Baseline Array of radio telescopes.
21. The semimajor axis of Pluto’s orbit is almost 40 au. From its orbit around Earth, the Hipparcos satellite measured stellar parallaxes to an accuracy of about 0.01 arcsecond. Suppose astronomers use this technique to measure parallax from Pluto’s orbit (over the course of half a Pluto “year”). What is the maximum distance they could measure?
A) 4 pc
B) 100 pc
C) 4000 pc
D) 8000 pc
22. What is the relationship between stellar parallax (p) measured in seconds of arc and distance (d) measured in parsecs?
A) d = 1/p2
B) d = 1/p
C) d = p
D) d = p2
23. Suppose astronomers want to measure the distance to a star in astronomical units. They would use the equation d (au) = x/parallax angle (arcsec). What is x?
A) 3.26
B) 360
C) 206,265
D) 3.0 × 108
24. A star is 80 pc from the Sun. Its apparent motion against the background sky, that is, its stellar parallax, as a result of Earth’s motion through 1 au is
A) 0.0125 arcsecond.
B) 0.0125 arcminute.
C) 0.0125 radian or 0.72°.
D) 80 arcseconds.
25. A particular star has an angle of parallax of 0.1 arcsec. What is the distance to this star?
A) about 10 ly
B) about 33 ly
C) about 0.1 ly
D) about 3.3 ly
26. A particular star is 20 pc away from Earth. What is the stellar parallax for this star?
A) 6 arcsec
B) 20 arcsec
C) 0.02 arcsec
D) 0.05 arcsec
27. Stellar parallax as small as 0.01 arcsec can be measured using telescopes on Earth. To what distance does this measurement correspond in space?
A) 500 pc
B) 200 pc
C) 0.01 pc
D) 100 pc
28. f a nearby star shows a parallax of 0.5 arcsec (when Earth moves through 1 au, by definition), what is its distance from Earth, in light-years?
A) 2 ly
B) 1.83 ly
C) 6.52 ly
D) 3.26 ly
29. The star Proxima Centauri has a parallax of 0.77 arcsec (the largest parallax known). How far is this star system from the Sun in light-years? (Careful with units!)
A) 4.24 ly
B) 0.41 ly
C) 1.33 ly
D) 0.75 ly
30. If astronomers measure the parallax of a star against the background stars and conclude that the star has a parallax of 0.004 arcsec, how far is the star from Earth?
A) 25 pc or 81.5 ly
B) 250 pc or 815 ly
C) 400 pc or 1300 ly
D) 0.004 pc or 0.013 ly
31. The Hipparcos satellite could measure stars up to approximately 150 pc away. What was the smallest parallax angle it could measure?
A) 150 arcsec
B) 1/150 arcsec
C) 1/150 degrees
D) 1/75 arcsec
32. The European Space Agency recently launched the Gaia mission, which will measure parallax angles down to 10–5 arcseconds. What distance does this correspond to?
A) 10–5 pc
B) 105 light-years
C) 10 kpc
D) 100 kpc
33. The Hipparcos satellite was able to measure parallax for stars out to about 150 pc. This distance includes roughly 2.5 million stars. What is the average number of stars in 1 cubic parsec?
A) 5.1 × 10–3
B) 0.18
C) 5.65
D) 8.84
34. The Hipparcos satellite was able to measure parallax for stars out to about 150 pc. This distance includes roughly 2.5 million stars. The new Gaia satellite should be able to measure the parallax of roughly a billion stars. Assuming the density of stars is approximately constant, what distance would this correspond to? (Hint: The volume of a sphere is proportional to the cube of the radius.)
A) 35 pc
B) 167 pc
C) 350 pc
D) 20 kpc
35. How far out into space can distances be determined using telescopes on Earth if stellar parallax values no smaller than 0.01 arcsec can be measured?
A) 10 pc
B) 100 pc
C) 500 pc
D) 2000 pc
36. Sirius, in Canis Major (the large hunting dog of Orion), is the brightest star in the northern hemisphere winter night sky. It has a parallax angle of 0.38 arcseconds. The brightest star in Orion’s other hunting dog, Canis Minor, is Procyon, with a parallax angle of 0.29 arcseconds. Vega, in Lyra (the Lyre [Harp]), is the brightest star in the northern summer night sky. It has a parallax angle of 0.13 seconds of arc. Which of these stars is farthest away?
A) Sirius
B) Procyon
C) Vega
D) The answer to the question cannot be determined from this information alone.
Section: 12-2
37. How much can astronomers learn about a star from a measurement of its apparent magnitude?
A) intrinsic brightness (the total light actually emitted by the star)
B) brightness the star would appear to have if it were exactly 10 pc from Earth
C) brightness of the star as it appears in Earth’s sky
D) total output of electromagnetic energy emitted at all wavelengths from the star
38. Apparent magnitude is a measure of a star’s
A) intrinsic brightness (actual light output).
B) size (diameter).
C) temperature.
D) brightness, as seen from Earth.
39. The relative brightness of a star as seen in Earth’s sky is called
A) absolute magnitude.
B) apparent magnitude.
C) surface temperature.
D) luminosity.
40. How many eleventh magnitude stars are required to equal the brightness of one first magnitude?
A) 10
B) 100
C) 1000
D) 10,000
41. Two of the brightest stars in Orion are Betelgeuse (apparent magnitude = 0.45) and Rigel (apparent magnitude = 0.15). From this information, one can determine
A) that Betelgeuse is brighter than Rigel.
B) that Betelgeuse is bigger than Rigel.
C) that Betelgeuse is farther away than Rigel.
D) None of these are correct.
42. A star of apparent magnitude +1 appears _____ than a star of apparent magnitude +2.
A) either brighter or fainter, depending on the distance to the stars,
B) farther away
C) brighter
D) fainter
43. A star of apparent magnitude +5 appears _____ than a star of apparent magnitude +3.
A) fainter
B) farther away
C) brighter
D) either brighter or fainter, depending on the distance to the stars,
44. As an observer moves closer to a star, which two of its properties change?
A) luminosity and absolute magnitude
B) luminosity and apparent brightness
C) absolute magnitude and brightness
D) apparent magnitude and brightness
45. Which of these stars (each of which is listed with its apparent magnitude) looks brightest when viewed from Earth?
A) tau Ceti; m = +3.49
B) alpha Centauri B; m = +1.34
C) Barnard’s star; m = +9.53
D) 61 Cygni A; m = +5.21
46. Which of these stars (each of which is listed with its apparent magnitude) would NOT be visible to the unaided eye on a clear night?
A) tau Ceti; m = +3.49
B) alpha Centauri B; m = +1.34
C) Barnard’s star; m = +9.53
D) 61 Cygni A; m = +5.21
47. A star of apparent magnitude +4.7 appears _____ than a star of apparent magnitude +4.8.
A) brighter
B) either brighter or fainter, depending on the distance to the stars,
C) farther away
D) fainter
48. A star of apparent magnitude +3.5 appears _____ than a star of apparent magnitude +3.3.
A) farther away
B) fainter
C) either brighter or fainter, depending on the distance to the stars,
D) brighter
49. A star of apparent magnitude –2 appears _____ than a star of apparent magnitude –3.
A) fainter
B) brighter
C) farther away
D) either brighter or fainter, depending on the distance to the stars,
50. A star of apparent magnitude –1.5 appears _____ than a star of apparent magnitude +2.0.
A) farther away
B) fainter
C) brighter
D) either brighter or fainter, depending on the distance to the stars,
51. A star of apparent magnitude +2.1 appears _____ than a star of apparent magnitude –1.2.
A) farther away
B) fainter
C) brighter
D) either brighter or fainter, depending on the distance to the stars,
52. The modern system of apparent magnitudes uses the star Vega as its basis. In this scheme Vega is defined to have an apparent magnitude of
A) 10.
B) 1.0.
C) 0.0.
D) –1.0.
53. The ancient Greek astronomer Hipparchus introduced the magnitude scale on which he called the brightest stars “first magnitude”. Today, the brightest star in the night sky is Sirius, with a magnitude of –1.4, considerably brighter than first magnitude. Why the discrepancy?
A) Sirius was formed since the era in which Hipparchus lived.
B) Sirius existed during Hipparchus’s lifetime, but it has obviously brightened considerably since then.
C) Hipparchus had poor eyesight and made many classification errors.
D) After using modern scientific instruments to measure the actual energy output of stars, astronomers modified the magnitude scale of Hipparchus.
54. Some stars are variable, with many properties that change over time. The statement that the apparent magnitude of a variable star has INCREASED indicates that its
A) brightness has increased.
B) surface temperature has decreased.
C) brightness has decreased.
D) surface temperature has increased.
55. A star that has an apparent magnitude of 0 would
A) be fainter than Spica (alpha Virginis), which has an apparent magnitude of +1.0.
B) be brighter than Deneb (alpha Cygni), which has an apparent magnitude of +1.2.
C) have infinite brightness since 1/0 = infinity.
D) not be emitting any light and therefore could not be seen from Earth.
56. The star Alphard has an apparent magnitude of 2.0, and the star Megrez has an apparent magnitude of 3.3. The only thing that can be said with certainty about Alphard is that it is _____ than Megrez.
A) brighter, as seen in Earth’s sky
B) more luminous
C) fainter, as seen in Earth’s sky
D) closer to Earth
57. When observers look out at the night sky, the number of stars with
A) each magnitude (first, second, etc.) is about the same.
B) smaller magnitude numbers is much larger than the number of stars with larger magnitude numbers.
C) larger magnitude numbers is much larger than the number of stars with smaller magnitude numbers.
D) magnitudes around 3 is larger than either the number with magnitudes around 2 or the number with magnitudes around 4.
58. If an observer looks out at a clear night sky with the unaided eye, the faintest stars the observer can see have magnitudes around
A) –6
B) 0
C) +6
D) +12
59. What is the ratio of the brightnesses of two stars if their apparent magnitudes differ by +1?
A) about 2.5
B) 100
C) 2, by definition
D) 10
60. Two stars whose apparent magnitudes differ from each other by 5 magnitudes have a ratio of brightnesses of
A) 25.
B) 10.
C) 100.
D) 2.5.
61. If star A has an apparent magnitude of +5 and star B has an apparent magnitude of +10, then
A) star A is twice as bright as star B.
B) star B is twice as bright as star A.
C) star A is 100 times as bright as star B.
D) star B is 100 times as bright as star A.
62. How many times brighter than a magnitude +4.0 star is a magnitude +3.0 star?
A) 100 times brighter
B) twice as bright
C) a factor of 4/3, or 1.333 times, brighter
D) 2.512 times brighter
63. How many times brighter is a star with an apparent magnitude of +1.0 than a star with an apparent magnitude of +6.0?
A) 100 times brighter
B) 5 times brighter
C) The question is incorrectly worded; the magnitude +6 star will be 100 times brighter than the magnitude +1 star.
D) 2.512 times brighter
64. How many second-magnitude stars would be needed in a close cluster to match the light intensity of a first-magnitude star?
A) about 2.5
B) 2
C) about 10
D) about 0.4, or 1/2.5
65. How many stars of sixth-magnitude would it take for a small cluster to appear as bright as a single first-magnitude star?
A) 105
B) 5
C) 6
D) 100
66. If a distant cluster were to be composed only of stars with apparent magnitude of +3, how many stars would there be in this cluster if its apparent magnitude matched that of a star with apparent magnitude of +1?
A) 2
B) 102, or 100
C) about 2.5
D) between 6 and 7
67. Sirius, visually the brightest star in Earth’s night sky, has an apparent magnitude of about –1.5, while the Andromeda Galaxy has an apparent magnitude of about +3.5. What is the ratio of their brightnesses, as seen by Earthbound observers?
A) The Andromeda Galaxy is 100 times brighter than Sirius.
B) The Andromeda Galaxy is 2 times fainter than Sirius.
C) The Andromeda Galaxy is 5 times brighter than Sirius.
D) The Andromeda Galaxy is 100 times fainter than Sirius.
68. How many fourth-magnitude stars would a star cluster need to have to appear as bright as a single second-magnitude star?
A) 2
B) 4
C) 2.512
D) 6.310
69. The faintest stars observable through the largest telescopes have apparent magnitudes of roughly m = 30. How many of these stars would it take to equal the brightness of Vega, which has m = 0?
A) 30
B) 30 2.512
C) 302.512
D) 2.51230
70. Vega is often used as the star to define an apparent magnitude of 0. Actually, the standard for 0 magnitude is the average of a group of stars including Vega. But the averaging must be done with care. If one takes the combined brightness of one 0.1-magnitude star and one –0.1-magnitude star and divides this brightness by two, the equivalent brightness is
A) one 0-magnitude star.
B) one star with a magnitude less than 0.
C) one star with a magnitude greater than 0.
D) two 0-magnitude stars.
Section: 12-3
71. A star’s absolute magnitude and its apparent magnitude have the same numerical value. How far is this star from Earth?
A) It is not possible for a star to have the same absolute and apparent magnitudes.
B) The star would have to be an infinite distance away.
C) 10 ly
D) 10 pc
72. The Sun’s luminosity is 3.83 1026 watts. By the time this energy reaches Earth, it has spread out so that it provides only 1370 watts to each square meter. The orbit of Mars has a mean radius of 1.53 au. How many watts of the Sun’s luminosity are provided to each square meter of the surface of Mars?
A) 34
B) 153
C) 585
D) 1578
73. Luminosity is measured in
A) watts.
B) watts per second.
C) watts per square meter.
D) parsecs.
74. A star has an absolute magnitude M = 1.69 and an apparent magnitude m = 1.04. How far away is this star?
A) 24.2 ly
B) 43.2 ly
C) 59.7 ly
D) 160.2 ly
75. How many times brighter does the Sun appear from Earth than it does from Neptune, which has an orbital radius of approximately 30 au?
A) 30
B) 30 × 2.512 = 75.4
C) (30)2 = 900
D) 4π (30)2 = 1130
76. Star A has luminosity LA = 100 LSun and it is 1000 pc away. Star B has the same luminosity as the Sun, LSun, and it is 100 pc away. What is true about the brightnesses of these two stars?
A) Star A is brighter than Star B.
B) Star B is brighter than Star A.
C) Star A and Star B have the same brightness.
D) It is not possible to answer the question without knowing LSun, the luminosity of the Sun.
77. What is the fundamental difference between absolute and apparent magnitude of a star?
A) The difference is +5 since absolute and apparent magnitude differ by this value by definition.
B) Apparent magnitude depends on the star’s temperature, whereas absolute magnitude is independent of temperature.
C) Apparent magnitude depends on the size of the star, whereas absolute magnitude is independent of this parameter.
D) Absolute magnitude is an intrinsic property of the star, whereas apparent magnitude depends on its distance from Earth.
78. Light leaving a point source spreads out so that the apparent brightness I of light per unit area varies with distance d according to which of these laws ( means “proportional to”)?
A) I = constant
B) I 1/d2
C) I d2
D) I 1/d
79. Suppose the distance between an observer and a lightbulb is doubled. How does its final brightness compare with its initial brightness?
A) The lightbulb appears 1/16 as bright.
B) The lightbulb appears 4 times brighter.
C) The lightbulb appears 1/2 as bright.
D) The lightbulb appears 1/4 as bright.
80. Suppose that two identical stars (they have the same total light output) are located so that star A is at a distance of 5 pc, and star B is at a distance of 25 pc from Earth. How will star B appear, compared with star A?
A) Star B will be 1/5 as bright as star A.
B) Star B will be 1/25 as bright as star A.
C) Star B will be 1/2.2 as bright as star A.
D) Star B will be 1/20 as bright as star A.
81. Two stars, P and Q, can be seen in the same region of Earth’s sky with the same apparent magnitude, but star Q is twice as far away as star P. What is the ratio of the luminosities of these stars (star P/star Q)?
A) 4
B) 2
C) 1/4
D) 1/2
82. The intensity of sunlight per square meter reaching Jupiter is approximately what fraction of that at Earth’s orbital distance? (Jupiter’s orbit has a semimajor axis of about 5 au.)
A) 25 times
B) about the same
C) 1/5
D) 1/25
83. What is the intensity of sunlight per square meter reaching Venus compared with this intensity at Earth’s orbital distance? (Venus’s orbit has a semimajor axis of about 0.7 au.)
A) about the same, since this intensity remains constant, following a law of nature
B) about 1.4
C) about 1.9
D) about 0.5
84. What is the ratio of the light energy that falls on a unit area of Mercury’s surface compared to that falling on a unit area of Earth’s Moon if Mercury is at 0.4 au and the Moon is at 1.0 au from the Sun?
A) 1
B) 6.25
C) 2.5
D) 16
85. The star Centauri C and the star Groombridge 34 B have the same apparent magnitude, but Centauri C is 1.3 pc away from Earth and Groombridge 34 B is 3.5 pc away. What is the luminosity of Groombridge 34 B compared with Centauri C?
A) 2.7 times brighter
B) 7.2 times fainter
C) 2.7 times fainter
D) 7.2 times brighter
86. For MOST stars, the
A) absolute magnitude is a larger number than the apparent magnitude.
B) apparent magnitude is a larger number than the absolute magnitude.
C) absolute magnitude and the apparent magnitude are numerically equal.
D) chances are about even of the apparent magnitude being larger or the absolute magnitude being larger.
87. Absolute magnitude is defined as the apparent magnitude that a star would have if
A) all the energy from the star were concentrated in the visual region.
B) it were located at exactly 10 ly from Earth.
C) it were located at exactly 10 pc from Earth.
D) it were located at exactly 10 au from Earth.
88. When comparing two stars, the one with the _____ must have the greater luminosity.
A) larger radius
B) higher surface temperature
C) smaller absolute magnitude
D) larger surface area
89. The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?
A) 32.6 ly
B) distance to the galactic center
C) 10 ly
D) 1 au
90. What observations of a star are necessary to determine the absolute magnitude of a star?
A) distance and temperature
B) apparent magnitude and temperature
C) just apparent magnitude since absolute magnitude is simply apparent magnitude + 5
D) apparent magnitude and distance
91. The Sun has an absolute magnitude of +4.8. How far away would Earth have to be for the Sun to be just barely visible to the unaided eye (sixth-magnitude)?
A) 1.2 pc
B) 6 pc
C) 17.4 pc
D) 22.4 pc
92. A particular star is at a distance of 20 pc from Earth. For this star, the apparent magnitude will have
A) a larger value than its absolute magnitude.
B) a smaller value than its absolute magnitude.
C) the same value as its absolute magnitude, since magnitude is independent of distance.
D) a larger or a smaller value than the absolute magnitude, depending on the temperature and diameter of the star.
93. A particular star is at a distance of 5 pc from Earth. For this star, the apparent magnitude will have
A) the same value as its absolute magnitude, since magnitude is independent of distance.
B) a smaller value than its absolute magnitude.
C) a larger or smaller value than its absolute magnitude, depending on the temperature and diameter of the star.
D) a larger value than its absolute magnitude.
94. The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4. From this information (assuming that the starlight has not been dimmed by interstellar clouds), one can say for sure that Alderamin is _____.
A) less than 10 pc away
B) brightest in blue light
C) brightest in red light
D) more than 10 pc away
95. The star Fomalhaut has an apparent magnitude of 1.15 and an absolute magnitude of 2.0. From this information (assuming that the starlight has not been dimmed by interstellar clouds), one can say for sure that Fomalhaut is _____.
A) brightest in blue light
B) less than 10 pc away
C) brightest in red light
D) more than 10 pc away
96. The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4. The star Merak has an apparent magnitude of 2.4 and absolute magnitude of 0.5. Assuming that neither star has been dimmed by interstellar clouds, one can say for sure that Merak is
A) the same distance as Alderamin from Earth.
B) farther away from Earth than Alderamin.
C) an intrinsically fainter star than Alderamin.
D) closer to Earth than Alderamin.
97. The star Phoenicis has an apparent magnitude of +3.4 and an absolute magnitude of –4.6. The North Star (Polaris) has an apparent magnitude of +2.0 and an absolute magnitude of –4.6. Assuming that no light has been absorbed or scattered by interstellar dust, one can say for sure that Polaris is
A) the same distance as Phoenicis from Earth.
B) closer to Earth than Phoenicis.
C) farther away from Earth than Phoenicis.
D) fainter than Phoenicis in the Earth’s sky.
98. A particular star has an apparent magnitude of +12 and an absolute magnitude of +5. What is the distance to this star?
A) 125 pc
B) 250 pc
C) 125 ly
D) 250 ly
99. A star is at such a distance that its apparent magnitude (m) is 10 magnitudes fainter than its absolute magnitude (M). How far away is it?
A) 10 pc
B) 100 pc
C) 1000 pc
D) 10,000 pc
100. A star whose absolute magnitude M is +2.2 is seen to have an apparent magnitude when viewed from Earth of +5.2. How far away is the star?
A) 40 pc
B) 12.3 pc
C) 130 pc
D) 3/5, or 0.6 pc
101. A star that is 100 pc distant from Earth has an apparent magnitude of m = +2.5. What is its absolute magnitude?
A) –7.5
B) +7.5
C) –2.5
D) –47.5
102. The star Arietis has an apparent magnitude of +2.7 and a distance of 52 ly. What is its absolute magnitude?
A) +1.7
B) –0.9
C) +6.2
D) +3.7
103. Three stars have the following absolute (M) and apparent (m) magnitudes:
Star A: M = 1.8 m = 3.8
Star B: M = 2.5 m = 9.5
Star C: M = 7.6 m = 15.1
Which star is farthest away from Earth?
A) Star A
B) Star B
C) Star C
D) cannot be determined from these data
104. Three stars have the following absolute (M) and apparent (m) magnitudes.
Star A: M = 1.8 m = 3.8
Star B: M = 2.5 m = 9.5
Star C: M = 7.6 m = 15.1
Which star is closest to Earth?
A) Star A
B) Star B
C) Star C
D) cannot be determined from these data
105. What is a star’s luminosity?
A) amount of energy received per second on 1 m2 of a planet’s surface exactly 1 au from the star
B) total energy emitted by the star into all space per second, measured in watts
C) apparent magnitude the star would have if it were located exactly 10 ly from Earth
D) apparent magnitude the star would have if it were located exactly 10 pc from Earth
106. The luminosity of a star is
A) its brightness as seen by people on Earth.
B) its brightness if it were at a distance of 10 pc (32.6 ly) from Earth.
C) its total energy output into all space.
D) another name for its color or surface temperature.
107. The luminosity of a star is a unique measure of its
A) total energy output.
B) velocity of recession away from Earth.
C) temperature.
D) physical size.
108. The Sun’s absolute magnitude is about +5. The brightest stars in the sky have absolute magnitudes of about –10. What is the luminosity of these stars compared with that of the Sun, assuming that they have similar spectral light distributions?
A) 1 million times less
B) 5 times less
C) 1 million times greater
D) 15 times greater
109. Two stars in Earth’s sky have the same apparent brightness. If neither of them is hidden behind gas or dust clouds, then one knows that they
A) must be at the same distance from Earth.
B) may be at different distances, in which case the nearer one must have the greater luminosity.
C) may be at different distances, in which case the farther one must have the greater luminosity.
D) must have the same temperature.
110. How bright (in absolute magnitude) are the intrinsically brightest stars in the universe?
A) +17
B) +1
C) 0
D) –10
111. How bright (in absolute magnitude) are the intrinsically faintest stars in the universe?
A) +1
B) +17
C) –10
D) 0
112. If the intrinsically brightest stars in Earth’s sky have absolute magnitudes of –10, how bright (in terms of total energy output per second) are these stars compared with the Sun, whose absolute magnitude is +4.8?
A) about 14.8 times brighter
B) about 800,000 times brighter
C) about 8000 times brighter
D) about 1015, or 1,000,000,000,000,000, times brighter
113. If the intrinsically faintest stars in Earth’s sky have absolute magnitudes of +17, how does their total energy output compare with that of the Sun, whose absolute magnitude is +4.8?
A) about 12.2 times lower
B) about 1012 or 1,000,000,000,000, times lower
C) about 7600 times lower
D) about 76,000 times lower
114. The technical designation for the bright star Regulus is Leonis. This means that Regulus is
A) the second brightest star in the constellation Leon the Astronomer.
B) the third brightest star in the constellation Leo the Leopard.
C) the brightest star in the constellation Leo the Lion.
D) a star of spectral type alpha in the constellation Leo.
Section: 12-4
115. The technique called photometry in stellar astronomy is the measurement of the
A) arrival times of photons from variable and pulsating stars to determine accurately the pulsation or rotation periods of these stars.
B) intensity of light from stars through several limited-bandpass filters from which surface temperature, variability, luminosity, and so on of stars can be determined.
C) relative absorption of light by different atoms and molecules in high-resolution spectra of starlight, from which stellar temperatures can be estimated.
D) precise positions and relative motions of stars in the Galaxy, from which galactic structure and overall rotation can be determined.
116. An astronomer is measuring the brightness of a particular star through a telescope, using different filters in the visual (yellow-green), violet, and ultraviolet regions. What is the name of the technique being used by this astronomer?
A) spectroscopy
B) geometry
C) interferometry
D) photometry
117. When observed through a set of photometric filters, a distant star is seen to be brightest through the ultraviolet filter, less bright through the blue filter, and faintest through the yellow filter. What conclusion can be drawn from this information, assuming no absorption of light between the star and Earth?
A) The question gives insufficient information to draw a conclusion about a star’s surface temperature.
B) The star has an intermediate temperature close to that of the Sun.
C) The star has a very high surface temperature.
D) The star has a very low surface temperature.
118. The difference in the brightness of a star as seen through two different colored filters, for example, blue and yellow, is directly related to which stellar property?
A) distance from Earth
B) luminosity
C) surface temperature
D) radius
119. A particular star appears brighter seen through a blue filter than seen through a yellow filter. Which of these surface temperatures is possible for this star?
A) 3000 K
B) 12,000 K
C) 4500 K
D) 6000 K
120. A particular star appears fainter seen through a blue filter than seen through a yellow filter. Which of these surface temperatures is possible for this star?
A) 12,500 K
B) 38,000 K
C) 8800 K
D) 3800 K
121. A particular star appears approximately equally bright when viewed through a blue filter and through a yellow filter. What is the approximate surface temperature of this star?
A) 6000 K
B) 12,000 K
C) 3000 K
D) It is not possible for a star to be equally bright at two different wavelengths.
122. Which of these MOST plausibly explains why the star Bellatrix in Orion looks bluish to the naked eye?
A) The spectrum of light emitted from Bellatrix peaks in the blue region of the spectrum, with almost all its light concentrated in the blue region of the spectrum.
B) The spectrum of light emitted from Bellatrix peaks in the ultraviolet region of the spectrum. Within the visible part of the spectrum, there is more emission in the blue than in any other color.
C) Bellatrix is moving toward Earth rapidly enough that its light appears appreciably blueshifted.
D) Bellatrix is made of blue material.
123. The Sun’s spectrum peaks in the green region (i.e., green is the most intense color in its spectrum). The spectrum of Rigel (the knee of Orion) peaks in the short-wavelength end of the visible spectrum. Compared with the Sun, Rigel is
A) cooler and redder.
B) hotter and redder.
C) cooler and bluer.
D) hotter and bluer.
124. The star Rigel, in the constellation Orion, appears brighter through a blue filter than it does through a yellow filter. Suppose that a second star is found that is slightly brighter than Rigel through the yellow filter but is much brighter than Rigel through the blue filter. From this information, one can say conclusively that the second star has
A) the same temperature but a lower luminosity.
B) a higher temperature.
C) a lower temperature.
D) the same temperature but a higher luminosity.
125. The star Regulus, in the constellation Leo, appears brighter through a blue filter than it does through a yellow filter. Suppose that a second star is found that has the same brightness as Regulus through the blue filter but is brighter than Regulus through the yellow filter. From this information, one can say conclusively that the second star has
A) a higher temperature.
B) the same temperature but a higher luminosity.
C) the same temperature but a lower luminosity.
D) a lower temperature.
126. Rigel, the bright star in the knee of Orion, has a surface temperature of about 12,000 K. Through which filter will it appear brightest?
A) ultraviolet
B) blue
C) yellow
D) red
127. A star has a surface temperature of 6000 K. Its spectrum registers a certain intensity in the green middle of the visible spectrum. Which of these must also be true of the star?
A) Violet is brighter than the green but the red is less intense.
B) Violet is less intense than the green but the red is more intense.
C) Violet and the red are both less intense than the green.
D) Violet and the red are both more intense than the green.
Section: 12-5
128. Astronomers originally classified the spectra of stars according to the strengths of their hydrogen lines. What new physical insight enabled a reinterpretation of these patterns in terms of surface temperature during the 1920s?
A) discovery of nuclear physics and how stars generate their energy
B) discovery of blackbody radiation and the blackbody curve
C) development of atomic physics and how atoms emit light
D) development of radio astronomy and the detection of molecules in space
129. For Balmer series lines to show up strongly in absorption in stellar spectra, significant numbers of hydrogen atoms must have electrons in the n = 2 energy level. What then does the appearance of these lines in a stellar spectrum describe about the temperature of the star’s surface?
A) The appearance of the lines describes very little about the temperature because hydrogen gas will show significant Balmer absorption, whatever the surface temperature.
B) The temperature must be high enough to ionize the hydrogen atoms by collision so that they can absorb from this level.
C) The temperature must be reasonably low so that no atoms will have electrons excited beyond this energy level (e.g., to n = 3).
D) The temperature must be reasonably high to excite the electrons to this level by collisions but not high enough to ionize the atoms.
130. If a certain star shows a strong absorption spectrum in hydrogen Balmer lines, the surface temperature of the star is hot enough that
A) virtually all of the hydrogen atoms are ionized.
B) many hydrogen atoms have electrons in the n = 2 energy level.
C) many hydrogen atoms have electrons in the n = 3 energy level.
D) many helium atoms have been converted to hydrogen atoms.
131. Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas absorbs visible light in the Balmer series?
A) There must be electrons at the n = 3 energy level for Balmer absorption to occur. If the gas is too cold, electrons are only in the n = 1 and n = 2 levels; if the gas is too hot, the gas is ionized and no electrons are left in the hydrogen atoms.
B) Electrons in hydrogen have to be at the n = 2 energy level to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state; if it is too hot, most atoms are ionized.
C) Electrons must be in the ground state n = 1 to undergo Balmer absorption. If the gas is too cold, electrons cannot be excited from this level; if the gas is too hot, there are no electrons left in the n = 1 level.
D) There must be sufficient continuum radiation from the stellar surface in the visible region to be absorbed by the hydrogen gas.
132. Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures—significantly below 10,000 K, for example?
A) The hydrogen atoms have to be hot enough to be ionized in order to show Balmer absorption.
B) There is no emitted continuum radiation at Balmer-line wavelengths when the gas is so cool, so absorption will not be seen.
C) Atoms need electrons that have been excited by high temperatures to the n = 2 level to undergo Balmer absorption.
D) Hydrogen atoms have no electrons in any energy levels at these temperatures.
133. The spectrum of an ordinary main-sequence star is a
A) continuum of colors, crossed by brighter lines caused by emission from the hot atoms and molecules on the star’s surface.
B) smooth continuum of color, peaking at a specific wavelength whose position depends on the star’s surface temperature.
C) series of emission lines, mostly from hydrogen, the major constituent of stellar surfaces, that occasionally overlap to produce sections of continuous color.
D) continuum of colors crossed by dark absorption lines caused by absorption by cooler atoms and molecules at the star’s surface.
134. The chemical makeup of the Sun’s surface can be determined by
A) taking a sample of the star’s surface with a space probe.
B) examining the chemicals present in a meteorite because it is part of the solar system.
C) measuring the components of the solar wind with Earth-orbiting spacecraft.
D) solar spectroscopy.
135. Very hot stars have weak hydrogen spectral lines. Why is this?
A) These stars contain very little hydrogen.
B) The hydrogen in the atmospheres of these stars is combined into molecules, and these have different spectra.
C) The electrons in the hydrogen atoms in these stars are all in their lowest energy levels, and they cannot radiate from these levels.
D) The hydrogen atoms in these stars are mostly ionized and hence cannot radiate.
136. The surface temperature of a nearby star can be determined MOST precisely by measuring what parameters?
A) position of the star on the H-R diagram
B) Doppler shift of the star’s spectral lines
C) relative strengths of emission lines from different atoms and ions in the star’s spectrum
D) relative strengths of absorption lines from different atoms (e.g., H, Ca) and molecules (e.g., TiO) in the star’s spectrum
Section: 12-6
137. Spectral classification of a star into the lettered categories, O, B, A, F, G, K, and M is carried out by
A) finding the wavelength of peak emission in the continuum spectrum of the star.
B) determining the relative mass of the star by the study of binary star motions, in order to place it into its proper mass classification.
C) determining the total energy emitted at all wavelengths by the star, taking account of the full spread of wavelengths and their distances, in order to place the star into its luminosity class.
D) examining the relative amounts of absorption caused by various neutral and ionized atoms in a stellar spectrum.
138. Spectral types of stars (e.g., O, B, A, F, G, K, and M) uniquely define their
A) sizes or radii.
B) absolute magnitudes.
C) luminosities.
D) surface temperatures.
139. The surface temperature of a nearby star can BEST be determined from spectral classification by examining the
A) pattern of spectral absorption lines from various atoms.
B) relative intensities of light measured through different photometric filters.
C) peak wavelength of the star’s continuous blackbody spectrum.
D) pattern of emission lines that are on the star’s spectrum.
140. Which of these sequences of stellar spectral classifications is in the correct order of INCREASING temperature?
A) K, M, G, F, A, B, O
B) A, B, F, G, K, M, O
C) M, K, G, F, A, B, O
D) O, B, A, F, G, K, M
141. The sequence of letters that is used to classify star surface temperatures, as determined by relative spectral absorption line strengths, in order of DECREASING temperature, is
A) A, B, F, G, K, M, O.
B) M, O, F, K, G, A, B.
C) O, F, M, G, A, B, K.
D) O, B, A, F, G, K, M.
142. The Sun’s classification in terms of its surface temperature, as determined from absorption lines in its spectrum, is
A) M9.
B) G2.
C) O1.
D) B2.
143. In the spectral classification scheme, what designation is given to a star just a little cooler than a K5 star?
A) K4
B) K6
C) M0
D) K0
144. In the spectral classification scheme, what designation is given to a star just a little hotter than an F8 star?
A) F7
B) F9
C) G8
D) A8
145. Among these spectral types, which signifies the hottest stellar surface temperature?
A) G
B) A
C) K
D) B
146. Which of these four spectral classifications signifies the coolest stellar surface temperature?
A) B
B) K
C) G
D) A
147. The spectral class of the star Enif is K2, while that of the Sun is G2. Which of these conclusions can be drawn about Enif from this information?
A) Enif is intrinsically fainter than the Sun.
B) Enif is intrinsically brighter than the Sun.
C) Enif is cooler than the Sun.
D) Enif is hotter than the Sun.
148. Which of these stellar classifications describes a star HOTTER than an F5 star?
A) F9
B) K2
C) M0
D) B2
149. Stars of spectral type O, the hottest blue-white stars, have spectra characterized by
A) the strongest hydrogen lines of any spectral type.
B) spectra of complex molecules.
C) very few spectral lines.
D) very intense spectral lines all across the spectrum.
150. What characterizes an A-type star?
A) They have the strongest hydrogen lines.
B) They have the strongest calcium lines.
C) They are the hottest stars.
D) They are the largest stars.
151. Classifying stars by spectral type is the same as categorizing them by
A) mass.
B) temperature.
C) radius.
D) age.
152. Absorption line strengths are used in the spectral classification of stars and the determination of surface temperatures. Which of these atomic or molecular constituents exhibits strong absorption lines in spectra from stars with very high surface temperature?
A) H
B) Ca II
C) He II
D) TiO
153. If the surface temperature of a star is very low, which of these atomic or molecular constituents will produce the MOST prominent absorption lines in its spectrum?
A) Fe II
B) TiO
C) Mg II
D) He II
154. Which of these molecules produces the strong absorption bands in the spectrum of a cool M-type star, as can be seen in Figure 12-5 in the text?
A) HCl, hydrogen chloride
B) CaI, calcium iodide
C) H2O, water vapor
D) TiO, titanium oxide
155. Which of these atoms or ions produces the strongest absorption lines in the spectra of stars with the highest surface temperatures?
A) He II, ionized helium
B) Fe I, neutral iron
C) Ca II, singly ionized calcium
D) H I, neutral hydrogen
156. Which of these atoms or ions produces strong absorption lines in the spectra of stars with relatively cool surface temperatures?
A) TiO, molecules of titanium oxide
B) Mg II, ionized magnesium
C) Ca II, ionized calcium
D) He I, neutral helium
157. The spectrum of a star shows these absorption line characteristics: very strong H, weaker Mg II and Si II, and no He I or Ca II lines. What is the spectral type of this star?
A) B
B) G
C) K
D) A
158. A star shows weak hydrogen Balmer lines but strong lines of neutral sodium. What is a likely explanation for this?
A) This particular star contains no hydrogen.
B) The hydrogen has been ionized.
C) The hydrogen is not receiving enough energy to populate the n = 2 level required for Balmer transitions.
D) The sodium lines are masking the hydrogen lines because these occur at the same wavelengths.
159. The spectrum of a very distant source shows spectral absorption lines of ionized helium, He II, and molecular absorption bands from titanium oxide, TiO. What could one conclude about this star?
A) The source is probably the spectrum of a binary system, two stars close together, a hot star and a cooler companion, unresolved as separate stars from Earth but contributing separate spectra.
B) The source must have a very hot atmosphere containing helium gas overlying a much cooler stellar surface.
C) The source must have a thick, cool atmosphere overlying a hot stellar atmosphere.
D) There must be cool, interstellar gas containing TiO between the star and Earth.
Section: 12-7
160. Which two fundamental parameters are MOST often used to place a particular star on a path of stellar evolution for comparison with theoretical models?
A) apparent magnitude and distance
B) apparent magnitude and temperature
C) luminosity, or total energy output, and distance
D) luminosity, or total energy output, and temperature
161. From its position on the Hertzsprung–Russell diagram in Figure 12-7 in the text, what can an astronomer conclude about the star Mira compared with the Sun?
A) Mira is cooler and redder but intrinsically brighter than the Sun.
B) Mira is cooler, redder, and intrinsically fainter than the Sun.
C) Mira is hotter than the Sun and intrinsically brighter.
D) Mira is hotter and bluer but intrinsically fainter than the Sun.
162. The Hertzsprung–Russell diagram is a plot of
A) apparent brightness against intrinsic brightness of a group of stars.
B) apparent brightness against distance for stars near the Sun.
C) luminosity against mass of a group of stars.
D) absolute magnitude (or luminosity) against temperature of a group of stars.
163. What are the two physical parameters of stars that are plotted on the Hertzsprung–Russell diagram?
A) mass and surface temperature
B) luminosity and mass
C) radius and mass
D) luminosity and surface temperature
164. Which two physical parameters of stars are plotted on the Hertzsprung-Russell diagram to show the systematics of a group of stars (e.g., a cluster)?
A) mass and apparent magnitude
B) luminosity and radius
C) luminosity and surface temperature
D) surface temperature and mass
165. In the Hertzsprung–Russell diagram in Figure 12-7 in the text, which of these lists is the correct sequence of stars in order of DECREASING absolute magnitude?
A) Deneb, the Sun, Sirius B, Procyon B
B) Sirius B, Deneb, Procyon B, the Sun
C) Sun, Procyon B, Deneb, Sirius B
D) Procyon B, Sirius B, the Sun, Deneb
166. In the Hertzsprung-Russell diagram in Figure 12-7 in the text, which of these lists is the correct sequence of stars in order of INCREASING temperature?
A) Sirius B, Deneb, Procyon B, the Sun
B) Deneb, the Sun, Sirius B, Procyon B
C) Sun, Procyon B, Deneb, Sirius B
D) Procyon B, Sirius B, the Sun, Deneb
167. Using Figures 12-7 and 12-8 from the text, determine which of these lists is the correct sequence of stars in order of INCREASING size or stellar radius.
A) Sirius B, the Sun, Betelgeuse, Mira
B) Mira, Betelgeuse, the Sun, Sirius B
C) Betelgeuse, Mira, the Sun, Sirius B
D) Sirius B, the Sun, Mira, Betelgeuse
168. As one moves upward and to the left on the H-R diagram, the stars become
A) cooler and redder.
B) hotter and redder.
C) cooler and bluer.
D) hotter and bluer.
169. Compared with a star in the middle of the Hertzsprung–Russell diagram, a star in the lower left of the diagram is
A) larger.
B) cooler.
C) smaller.
D) brighter.
170. As one moves upward and to the right on the H-R diagram, stars become
A) hotter and brighter.
B) hotter and dimmer.
C) cooler and dimmer.
D) cooler and brighter.
171. Compared with a star in the middle of the Hertzsprung–Russell diagram, a star in the upper right of the diagram is
A) fainter.
B) hotter.
C) larger.
D) nonexistent because there are no stars that appear in the upper right of the diagram.
172. Where on the Hertzsprung–Russell diagram do MOST stars near the Sun congregate?
A) white dwarf area
B) supergiant area
C) giant area
D) main sequence
173. The equation for the luminosity of a star in terms of its surface temperature is
L = (surface area) σT4 where σ is the Stefan–Boltzmann constant. This suggests that when a plot is made of luminosities versus temperature
A) stars of the same temperature but different radii should occupy different points on the plot.
B) all stars should plot along the line.
C) larger stars must have higher temperatures.
D) smaller stars must have higher temperatures.
174. What fraction of the stars surrounding the Sun are main-sequence stars?
A) almost all, about 90%
B) There are no main-sequence stars close to the Sun.
C) roughly half, about 55%
D) very few, about 20%
175. If the surface temperatures of white dwarf stars are 4 times that of the Sun, and energy output per unit area of a star depends on the fourth power of the temperature by the Stefan–Boltzmann relation, why are white dwarfs intrinsically so faint?
A) White dwarfs are very small.
B) White dwarfs have very thin atmospheres that do not emit continuum radiation but only line emissions, like a low-density gas.
C) White dwarfs are shrouded in very thick atmospheres.
D) White dwarfs are moving rapidly away from the Sun and their spectra are extremely redshifted, hence they appear faint at visible wavelengths.
176. Measurements indicate that a certain star has a very high luminosity (100,000 times as bright as the Sun) and yet is relatively cool (3500 K). How can this be?
A) The star must be quite small.
B) The star must be very large.
C) There must be an error in observation because no star can have these properties.
D) The star must be in the upper part of the main sequence.
177. Listed below are parameters of stars that astronomers obtained from their measurements. Which of these conclusions is obviously NOT possible, based on the positions of these stars on the Hertzsprung–Russell diagram in Figure 12-8 in the text? (Ls and Rs are the luminosity and radius of the Sun, respectively.)
A) luminosity = Ls, radius = Rs, temperature = 6000 K; conclusion: main-sequence star
B) luminosity = 104 Ls, radius = 100 Rs, temperature = 5000 K; conclusion: red giant star
C) luminosity = Ls, radius = 1/10 Rs, temperature = 20,000 K; conclusion: white dwarf star
D) luminosity = 1/100 Ls, radius = 1/100 Rs, temperature = 20,000 K; conclusion: white dwarf star
178. Using the Hertzsprung–Russell diagram (Figure 12-7 in the text), determine which type of star has these characteristics: surface temperature of 40,000 K and luminosity 100,000 times that of the Sun.
A) cool, red, main-sequence star
B) hot, blue, main-sequence star
C) white dwarf
D) red giant
179. Using the Hertzsprung–Russell diagram (Figure 12-7 in the text), determine which type of star has these characteristics: surface temperature 10,000 K and luminosity 1/100 times that of the Sun.
A) red supergiant
B) main-sequence star
C) white dwarf
D) red giant
180. A red supergiant star is found to have a surface temperature of 2500 K and a luminosity 100,000 times that of the Sun. Use the Hertzsprung–Russell diagram in Figure 12-8 in the text to determine its approximate radius compared with that of the Sun.
A) about 10 times larger
B) about 100 times larger
C) about 1000 times larger
D) almost the same
181. What will be the intrinsic brightness or luminosity of a white dwarf star that has the same temperature as the Sun? See Figure 12-7 in the text.
A) 4 times the Sun’s luminosity
B) Because it has the same surface temperature, the white dwarf will have the same brightness.
C) 10–2 of the Sun’s luminosity
D) 10–4 of the Sun’s luminosity
182. See Figure 12-8 in the text. A white dwarf star whose temperature is the same as that of the Sun will have a radius that is
A) 10 times smaller than that of the Sun.
B) the same size as the Sun’s.
C) 2 times smaller than that of the Sun.
D) 100 times smaller than that of the Sun.
183. Two stars are found to have the same luminosity. However, one star has twice the surface temperature of the other. From this information, what can one determine about their radii?
A) The hotter star has half the radius of the cooler star.
B) The cooler star has half the radius of the hotter star.
C) The hotter star has a quarter the radius of the cooler star.
D) Nothing can be determined about the radii from this information.
184. A typical white dwarf has a surface temperature about 4 times that of the Sun and a radius about 1 percent that of the Sun. What can one determine about the luminosity of a typical white dwarf from this information?
A) The white dwarf will be less luminous than the Sun.
B) The white dwarf and the Sun will have about the same luminosity.
C) The white dwarf will be more luminous than the Sun.
D) Nothing can be concluded about the relative luminosities from this information.
185. Spica (in Virgo) and Hador (in Centaurus) have about the same temperature. However, Hador has roughly 4 times the luminosity of Spica. What can one determine about the relative radii of these two stars? Spica is about
A) the same diameter as Hador.
B) half the diameter of Hador.
C) one-quarter the diameter of Hador.
D) twice the diameter of Hador.
186. Two stars have the same luminosity (or absolute magnitude). One star is spectral class B and the other is spectral class K. From this information, one knows that the
A) K-type star is larger than the B-type star.
B) B-type star is larger than the K-type star.
C) B-type star is hotter but can be larger, smaller, or the same size as the K-type star.
D) K-type star is hotter but can be larger, smaller, or the same size as the B-type star.
187. The star Canis Majoris has an absolute magnitude of –2.4 and a spectral class of B2. Using Figures 12-7 and 12-8 from the text, how would Canis Majoris be classified?
A) B-type white dwarf
B) B2 III
C) B2 V
D) B2 I
Section: 12-8
188. A particular star has an absolute magnitude of +12 and a spectral class of A5. Using Figures 12-7 and 12-10 from the text, how would this star be classified?
A) A5 I
B) A-type white dwarf
C) A5 V
D) A5 III
189. By what standard technique did astronomers in the 1930s originally determine the luminosity class (I, II, III, IV, or V) of a star?
A) combining the apparent magnitude with the measured distance to the star
B) observing the diameter of the star on a photographic plate or CCD image
C) timing how long it takes for the star to be eclipsed by a companion in an eclipsing binary star system
D) studying the absorption lines in the star’s spectrum
190. What is the physical reason astronomers can find the luminosity class (I, II, III, IV, or V) of a star using the star’s spectrum?
A) The wavelength of maximum emission (given by Wien’s law) is affected by the size of the star.
B) The relative amounts of hydrogen, helium, and other elements are different for stars of different luminosity classes.
C) The absorption lines in the spectrum are affected by the density and pressure of the star’s atmosphere.
D) The absorption lines in the spectrum are affected by the star’s surface temperature.
191. A star with a surface temperature of 5000 K and a luminosity greater than 104 times that of the Sun is a member of which luminosity class?
A) IV, subgiant
B) V, main sequence
C) III, giant
D) I, supergiant
192. Which of these CANNOT be determined by examining a star’s spectrum?
A) the star’s spectral class
B) the star’s neutrino flux
C) the star’s luminosity class
D) the star’s radial motion
193. It was discovered that stars of the same temperature can include stars of different radii. The response to this finding was
A) to refine the spectral classification scheme by introducing subheadings 0–9.
B) to revise the spectral classification to start with O rather than A.
C) to define the luminosity classes.
D) to invent the H-R diagram.
194. White dwarfs are NOT included in the luminosity classification because they are
A) not yet active stars; they have not yet begun nuclear reactions.
B) no longer producing energy by nuclear reactions.
C) no longer radiating energy away.
D) too small.
195. How are white dwarfs treated in the luminosity class definitions?
A) They are considered a subgroup of main sequence stars, class Vb.
B) They are class VI.
C) They are not given a classification because they have not yet begun to produce energy by nuclear fusion.
D) They are not given a classification because they no longer create energy by nuclear fusion.
196. A star with a surface temperature of 4000 K and a luminosity of about 10–2 times that of the Sun is a member of which luminosity class? See Figure 12-10 from the text.
A) III, giant
B) I, supergiant
C) II, bright giant
D) V, main sequence
197. The star Hadar is classified as B1 II, which means that it is a
A) cool supergiant.
B) hot dwarf.
C) cool giant.
D) hot supergiant.
198. The star Arcturus is classified as K2 III, which means that it is a
A) hot giant.
B) cool supergiant.
C) cool giant.
D) cool main-sequence star.
199. The star Spica is classified as B1 V, which means that it is a
A) hot main-sequence star.
B) cool giant.
C) hot supergiant.
D) cool main-sequence star.
200. Barnard’s star, one of Earth’s near neighbors, is classified as M5 V. This means that it is a
A) cool main-sequence star.
B) hot main-sequence star.
C) cool giant.
D) cool supergiant, a huge star.
201. Which of these spectral luminosity classes corresponds to a red supergiant?
A) M2 I
B) B7 I
C) M3 V
D) G2 III
202. The star Elnath is classified as B7 III and the star Al Na’ir is classified as B7 IV. Compared with Al Na’ir, Elnath has about the same
A) surface temperature but is intrinsically much fainter.
B) intrinsic brightness but is considerably cooler.
C) surface temperature but is intrinsically much brighter.
D) intrinsic brightness but is considerably hotter.
203. The spectral luminosity class of the star Spica is B1 V, and that of the star Ceti is G8 V. From this information, one knows that Ceti is _____ Spica.
A) cooler but has the same luminosity as
B) cooler and has a lower luminosity than
C) hotter but has the same luminosity as
D) hotter and has a lower luminosity than
204. A particular star has an absolute magnitude of 0 and a spectral class similar to that of the Sun. Using Figure 12-10 in the text, how would this star be classified?
A) G2 V
B) G-type white dwarf
C) G2 I
D) G2 III
205. See Figure 12-10 in the text. The star Canis Majoris has an absolute magnitude of –2.4 and a spectral luminosity class of B2 V. The star Crucis has a spectral class of M4 and the same absolute magnitude as Canis Majoris. The spectral luminosity class of Crucis is probably
A) M-type white dwarf.
B) M4 II.
C) M4 Ia.
D) M4 V.
206. Two stars, one classified A4 V and the other A4 III, have the same apparent magnitude. There is no significant amount of absorption of starlight by interstellar material. From this information one knows that the A4 V star is _____ than the A4 III star.
A) cooler
B) closer to the Sun
C) farther from the Sun
D) hotter
207. Two stars, one classified A4 V and the other F8 V, have the same apparent magnitude. There is no significant amount of absorption of starlight by interstellar material. From this information one knows that the A4 V star is _____ the F8 V star.
A) farther from the Sun than
B) at the same distance from the Sun as
C) smaller than
D) closer to the Sun than
Section: 12-9
208. What is spectroscopic parallax?
A) apparent change in position of the absorption lines in a star’s spectrum due to the Doppler shift caused by Earth’s motion around the Sun
B) apparent change in position of a nearby star compared with distant background stars due to the motion of Earth around the Sun
C) change in position of the absorption lines in a star’s spectrum due to the Doppler shift caused by the star’s motion around the center of mass in a binary star system
D) distance to a star measured using the spectral luminosity class of the star and the inverse-square law
209. Which one of these is NOT needed to compute a distance to a star by the spectroscopic parallax method?
A) the mathematical relationship among distance, absolute magnitude, and apparent magnitude
B) the star’s stellar parallax
C) the star’s apparent magnitude
D) the star’s luminosity
210. Which of these possible factors MOST seriously limits the accuracy of spectroscopic parallax?
A) Stars of the same spectral luminosity class can have a range of temperatures.
B) It is difficult to accurately measure angular displacement for distant stars.
C) Stars of the same spectral luminosity class can have a range of absolute magnitudes.
D) It is not possible to accurately classify the spectral luminosity of even a nearby star.
Section: 12-10
211. Two stars in a binary system orbit around a common point that is
A) exactly midway between the two stars.
B) closer to the less massive star.
C) closer to the more massive star.
D) inside one of the stars.
212. Which of these is not a type of true binary system, or, in other words, that the stars are NOT physically associated with each other?
A) optical double
B) visual binary
C) spectroscopic binary
D) eclipsing binary
213. When two stars of unequal mass orbit each other under their mutual gravitational attraction, where is the center of mass of the system located?
A) point halfway between the centers of the stars
B) point between the stars, closer to the less massive star
C) center of the more massive star
D) point between the two stars, closer to the more massive star
214. What proportion of visible stars in Earth’s nighttime sky are members of multiple-star systems, such as binary stars?
A) less than 1 percent
B) More than 50 percent
C) only about 1/4, or 25 percent
D) close to 100 percent
215. Which of these statements about measuring the mass of an isolated star (a star that is not in a binary star system) is CORRECT?
A) The mass of the star can be measured accurately in several ways.
B) The mass of the star can be measured accurately only if its luminosity and temperature can be measured.
C) The mass of the star can be measured accurately only if its distance can be found.
D) The mass of the star cannot be measured accurately.
216. What is the only way to measure directly the mass of a star accurately?
A) Measure its distance using trigonometric parallax and its brightness using photometry.
B) It is not possible to measure the mass of a star.
C) Measure its spectral type and luminosity class, then use the H-R diagram.
D) Measure its gravitational effect on another object.
217. How do astronomers measure the masses of stars directly?
A) by observing the star’s brightness at different wavelengths (colors)
B) by observing the motion of two stars in a binary star system
C) by measuring the star’s brightness, temperature, and distance
D) by measuring the star’s brightness and obtaining its radius using the H-R diagram
218. Which important stellar parameter can be derived from the study of binary stars mutually bound to each other by gravitational forces?
A) stellar masses
B) distances of the stars from Earth
C) ages of the stars
D) surface temperatures of the stars
219. Which important property of stars can be BEST determined by observations of binary stars systems?
A) stellar mass
B) surface temperature
C) distance from Earth
D) pulsation period
220. One important aspect of the study of binary star systems, as distinct from single stars, is that it provides a
A) measurement of the masses of stars.
B) measurement of the surface temperatures of stars.
C) verification of the Doppler equation for wavelength shift of light from moving objects.
D) measurement of the composition (abundances of elements) inside stars.
221. How do two unequal-mass stars in a binary star system move around each other, in general?
A) The stars move in a single circular orbit around the same center and always on opposite sides from each other.
B) The stars move in straight lines, back and forth past each other.
C) The low-mass star moves in a circular orbit around the high-mass star, which remains stationary.
D) The stars move in elliptical orbits about a common center of mass.
222. Which of these statements is NOT true about the center of mass of a binary star system?
A) The center of mass is always on the line joining the two stars.
B) The center of mass is simultaneously a focus of the ellipse of each star’s motion.
C) The center of mass is always more distant from the more massive star.
D) The center of mass can move with respect to the more distant background stars.
223. To determine the sum of the masses of a visual binary star system, what needs to be measured?
A) temperatures and periods of the stars
B) distance from Earth and the semimajor axis of the orbit of one star relative to the other
C) periods and the semimajor axes of the stars
D) temperatures and distances from Earth of the stars
224. Which one of these properties is NOT needed to determine individual masses in a binary star system?
A) the distance to the binary system
B) the plane of the orbit of the two stars
C) the relative sizes of the orbits of the two stars
D) the absolute magnitude of at least one star
225. What is the difference between an optical double star and a visual binary star?
A) An optical double is an illusion—the stars are at vast distances from each other and are not actually orbiting each other—whereas in a visual binary, the stars are actually orbiting each other.
B) There is no difference; they are two names for the same thing.
C) The stars in an optical double star are actually orbiting each other, whereas a visual binary is an illusion. The stars are at vast distances from each other and are not actually orbiting each other.
D) Optical double stars can be seen as separate stars only through a telescope, whereas visual binaries can be seen with the unaided eye (e.g., the star Mizar in the Big Dipper’s handle).
226. For a pair of stars to be classified as an optical double, which one of these conditions must be true?
A) The stars must lie in almost the same direction from Earth but must not be orbiting around each other.
B) The stars must be orbiting around each other, and one must periodically cross in front of the other (i.e., it must eclipse the other) as seen from Earth.
C) The stars must be orbiting around each other, and absorption or emission lines from both stars must be visible in the spectrum.
D) The stars must be orbiting around each other, and both stars must be visible through telescopes from Earth.
227. For a pair of stars to be classified as a visual binary, which one of these conditions must be true?
A) The stars must be orbiting around each other, and both stars must be visible through telescopes from Earth.
B) The stars must be orbiting around each other, and absorption or emission lines from both stars must be visible in the spectrum.
C) The stars must be orbiting around each other, and one must periodically cross in front of the other (i.e., it must eclipse the other) as seen from Earth.
D) The stars must lie in almost the same direction from Earth but must not be orbiting around each other.
228. The star Algol in the constellation Perseus has these unusual characteristics. Every 68.75 hours its brightness dims suddenly from apparent magnitude 2.3 to apparent magnitude 3.5 and remains there for a few hours before returning just as suddenly to 2.3. In addition, halfway through this 68.75-hour period, the apparent magnitude becomes slightly dimmer than 2.3 for a few hours and then returns to 2.3. From this information alone it is possible to classify Algol as a(n)
A) optical double.
B) eclipsing binary.
C) totally eclipsing binary.
D) partially eclipsing binary.
229. In a particular binary star system, only one star is visible because the other star is too faint to see at that distance. An astronomer measures the size (semimajor axis) and period of the orbit of the visible star. From this information, the astronomer
A) cannot calculate anything about the mass—both stars have to be visible to do so.
B) can calculate the mass of each star.
C) can calculate the sum of the masses of the two stars but not the mass of each star separately.
D) can calculate the mass of the visible star but not that of the unseen star.
230. An astronomer is observing a binary system with two stars of masses M1 and M2. She determines a, the semimajor axis (also the average distance between the stars) and P, the period of their motion. Using this information in Kepler’s third law she can calculate
A) M1 or M2 but not both.
B) M1/M2.
C) M1 + M2.
D) both M1 and M2.
231. A particular star in a binary star system orbits the other in an elliptical orbit with a semimajor axis of 3 au and a period of 5 years. What is the sum of the masses of the two stars in the system?
A) 0.9
B) 1.1
C) 13.9
D) 0.07
232. If the Sun were orbited by a star of 1.8 solar masses at Jupiter’s distance of 5.2 au (or, more precisely, the Sun and the other star were orbiting each other 5.2 au apart), what would be the orbital period of the system? (It might be useful to compare the answer with the actual orbital period of Jupiter, 11.9 years.)
A) 7.1 years
B) 9.4 years
C) 50.2 years
D) 11.3 years
233. Two stars of equal mass form a visual binary system. The separation between the two stars is 4 au and the period of the orbital motion is 8 years. What is the mass of each star relative to the mass of the Sun?
A) 1
B) 1/2
C) 1/4
D) 2
234. An eclipsing binary system consists of
A) a star that is periodically eclipsed by the Moon.
B) two stars that periodically eclipse each other, as seen from Earth.
C) two stars in which spectral lines move back and forth periodically due to Doppler shift, indicating mutually orbiting stars.
D) two mutually orbiting and gravitationally bound stars that are close enough to be resolved when viewed from Earth.
235. The light intensity from a particular star remains essentially constant except for short and regular decreases, after which it increases again to its constant value. What is the MOST plausible explanation for this phenomenon?
A) One star is regularly eclipsing its companion as they move in mutual orbits when the plane of those orbits is close to Earth’s line of sight.
B) A variable star is pulsating in size, temperature, and intensity.
C) The star is undergoing periodic supernova events.
D) Shells of absorbing gas and dust are being periodically ejected from the star’s surface and are subsequently dispersing into space.
236. Which of these observations would NOT be an indication of a binary star system?
A) The “star” appears to move in a straight line against a background field of stars.
B) A “star” appears to become periodically dimmer and then brighter for a few hours at a time.
C) A “star” image periodically separates into two distinct images and then blends again.
D) The “star” appears to wiggle in its path across Earth’s sky against the background stars.
237. What condition is necessary on Earth to see eclipses of stars in binary star systems?
A) The stars must have very similar surface temperatures, whatever the inclination of their orbital plane to the line of sight, to see a significant eclipse.
B) The line of sight from Earth to the star system must be very close to perpendicular to the orbital plane of the stars.
C) The line of sight from Earth to the star system must be in or very close to the orbital plane of the stars.
D) One of the stars must be much bigger than the other so that it can hide its smaller companion when the orbital plane is at a large angle to the line of sight.
238. An eclipsing binary system consists of
A) two stars orbiting each other in which periodic spectral line shifts due to Doppler shift are measured.
B) two stars that are clearly resolved as separate but orbiting each other and obviously gravitationally bound to each other.
C) a star that is periodically eclipsed by the Moon.
D) two stars whose combined light output toward Earth varies regularly as one star periodically moves in front of the other.
239. Which of these major perturbations can occur to a close binary system and radically alter the evolution and behavior of the two individual stars?
A) gravitational disturbance of one star’s motion by its companion to force it to move in an orbit
B) transfer of matter from one star to its companion
C) heating of the localized areas of the atmosphere of one star by its companion
D) eclipsing of the light from one star by the other when viewed from Earth
240. What particular and very important phenomenon frequently occurs in binary star systems where the stars are very close together?
A) The less massive star, in its elliptical orbit, repeatedly passes through the thin, extended atmosphere of the second star, producing periodic rises and falls in light output from the star system.
B) The radiation from the hotter star slowly heats and evaporates away the cooler star.
C) Mass lost from one star is deposited on its companion.
D) The less massive star spirals slowly into its more massive companion because of tidal interactions.
241. The light curve made of a pair of eclipsing binaries will exhibit dips in intensity. The bottoms of these dips can have different shapes. How do astronomers interpret this?
A) A flat bottom means that one is viewing the system along the long (semimajor) axis.
B) A flat bottom means that the stars are experiencing a total eclipse.
C) A rounded bottom means that the stars are exhibiting a partial eclipse.
D) A V-shaped bottom means that one is viewing the system along the short (semiminor) axis.
Section: 12-11
242. Use the Hertzsprung–Russell diagram (Figure 12-7) and the mass-luminosity relation (Figure 12-15) in the text, to estimate the mass of Vega, an AO V main-sequence star with a surface temperature of about 10,000 K.
A) between 1.5 and 5.0 solar masses
B) about 10 solar masses
C) less than 1.0 solar mass
D) between 5.0 and 10.0 solar masses
243. A simple relationship exists between mass and luminosity for
A) all stars.
B) main-sequence stars.
C) giant stars and main-sequence stars.
D) white dwarf stars.
244. Which sentence describes the relationship between mass and luminosity of stars on the main sequence?
A) The luminosity of stars increases with mass up to a peak around 1 solar mass, then decreases as the mass continues to increase.
B) Luminosity is independent of the stellar mass.
C) The larger the stellar mass, the larger is the luminosity.
D) The greater the stellar mass, the less is the luminosity.
245. As one moves along the main sequence, the masses of stars
A) show no obvious relationship to temperature.
B) increase with increasing temperature.
C) decrease with increasing temperature.
D) remain relatively constant.
246. Where are the MOST massive stars to be found in the main sequence of a Hertzsprung–Russell diagram?
A) upper left end
B) Main-sequence stars all have approximately the same mass, by definition.
C) center
D) lower right end
247. Which of these could plausibly be the mass of a main-sequence star that has a luminosity 1000 times greater than that of the Sun?
A) 105 solar masses
B) 5 solar masses
C) 0.1 solar mass
D) 1000 solar masses
248. Which of these types of main-sequence stars would have the LARGEST mass?
A) M
B) A
C) O
D) G
249. Using the Hertzsprung–Russell diagram in Figure 12-7 in the text, and the mass-luminosity relationship for main-sequence stars shown in Figure 12-15 in the text, which of these lists is the correct sequence of stars in INCREASING order of mass?
A) Regulus, Barnard’s Star, Sun, Altair
B) Barnard’s Star, Altair, Sun, Regulus
C) Barnard’s Star, Sun, Altair, Regulus
D) Regulus, Altair, Sun, Barnard’s Star
250. Is there a relationship between the mass of a main-sequence star and its luminosity?
A) No. Large masses can have low luminosities and vice versa.
B) Yes. Mass and luminosity are related linearly: A star twice as massive has twice the luminosity.
C) Yes. The mass and luminosity are related, but not linearly: A star twice as massive has more than twice the luminosity.
D) Yes, but surprisingly there is an anticorrelation: Larger masses have smaller luminosities.
Section: 12-12
251. The radial velocity curve of a star in a binary star system is a plot against time of the
A) speed of the star in a direction perpendicular to the line of sight to the star.
B) position of the star in celestial coordinates.
C) variation of Doppler shift of the star’s spectral lines and hence of its speed toward or away from Earth.
D) temperature of the star as determined from the movement of the peak wavelength of its spectrum.
252. An astronomer looks through a telescope and identifies a source that appears visually to be a single star. However, the source is later determined to be a binary system looking at its spectrum. Which of these spectral features would NOT characterize it as a binary?
A) The spectrum includes spectral lines associated with two different spectral types.
B) The sets of spectral lines move periodically to slightly higher frequencies and then slightly lower frequencies.
C) As the lines from one spectral type are moving toward higher frequencies, the lines from the other spectral type are moving toward lower frequencies.
D) The spectral lines from one spectral type become periodically brighter while the lines from the other spectral type become dimmer.
253. Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again. Explain.
A) The effect of the gravitational field of one star on the atoms of the second star periodically produces spectral line shifts.
B) The magnetic field of one star produces Zeeman periodic splitting of spectral lines in atoms of the second star.
C) Oscillations on the surfaces of the stars lead to Doppler-shifted lines.
D) Motion toward and away from Earth during their orbital motion results in Doppler shift of light from these stars at times and no shift when the stars are moving perpendicular to the line of sight.
254. What is a spectroscopic binary?
A) an instrument for taking spectra of two sources simultaneously
B) a binary system detected through the shifting spectral lines of its stars
C) a binary system in which one star moves directly in front of the other
D) a pair of stars that are very close to each other on the sky but are not physically related