Chapter 12

25 July 2022
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question
Before we can use parallax to measure the distance to a nearby star, we first need to know __________. the month in which the star is observed the Earth-Sun distance the Sun's mass the distance to the nearest star besides the Sun
answer
the Earth-Sun distance
question
Which of the following is a valid way of demonstrating parallax for yourself? Get a camera, and photograph a person who is running back and forth. Look up at a star, and notice how it moves toward the western horizon during the night. Hold up your hand in front of your face, and move it slowly back and forth. Hold up your hand in front of your face, and alternately close your left and right eyes
answer
Hold up your hand in front of your face, and alternately close your left and right eyes
question
What is the cause of stellar parallax? Stellar parallax is caused by the gradual motion of stars in the local solar neighborhood. the gradual change in the patterns of the constellations over thousands of years. Earth's orbit around the Sun. the varying speed of Earth in its orbit around the Sun.
answer
Earth's orbit around the Sun
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The more distant a star, the __________. slower its parallax occurs larger its parallax angle faster its parallax occurs smaller its parallax angle
answer
smaller its parallax angle
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Approximately what is the parallax angle of a star that is 20 light-years away? 0.33 arcsecond 4.5Γ—10βˆ’5 arcsecond 0.0072 arcsecond 0.16 arcsecond
answer
0.16 arcsecond
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Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years? 8.7 light-years 2.1 light-years 1 light-year 3.3 light-years
answer
3.3 light-years
question
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________. more luminous, hotter, larger, and more massive more luminous, hotter, smaller, and less massive less luminous, cooler, larger, and more massive less luminous, cooler, smaller, and less massive
answer
less luminous, cooler, smaller, and less massive
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Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________. hotter and larger in radius cooler and larger in radius cooler and smaller in radius hotter and smaller in radius
answer
cooler and larger in radius
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Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________. hotter and larger in radius cooler and larger in radius cooler and smaller in radius hotter and smaller in radius
answer
hotter and smaller in radius
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If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would get larger. get smaller. stay the same.
answer
get smaller
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What do we need to measure in order to determine a star's luminosity? apparent brightness and mass apparent brightness and temperature apparent brightness and distance
answer
apparent brightness and distance
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What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system? the time between eclipses and the average distance between the stars the period of the binary system and its distance from the Sun the velocities of the stars and the Doppler shifts of their absorption lines
answer
the time between eclipses and the average distance between the stars
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Which of these stars has the coolest surface temperature? an A star an F star a K star
answer
a K star
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Which of these stars is the most massive? a main-sequence A star a main-sequence G star a main-sequence M star
answer
a main-sequence A star
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Which of these stars has the longest lifetime? a main-sequence A star a main-sequence G star a main-sequence M star
answer
a main-sequence M star
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Which of these stars has the largest radius? a supergiant A star a giant K star a supergiant M star
answer
a supergiant M star
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Which of these stars has the greatest surface temperature? a 30 MSun main-sequence star a supergiant A star a Cepheid variable star
answer
a 30 MSun main-sequence star
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Which of these star clusters is oldest? a cluster whose brightest main-sequence stars are white a cluster whose brightest main-sequence stars are yellow a cluster containing stars of all colors
answer
a cluster whose brightest main-sequence stars are yellow
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The total amount of power (in watts, for example) that a star radiates into space is called its _________. absolute magnitude flux luminosity apparent brightness
answer
luminosity
question
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples? Its apparent brightness will decrease by a factor of 3. Its apparent brightness will increase by a factor of 3. Its apparent brightness will increase by a factor of 9. Its apparent brightness will decrease by a factor of 9.
answer
Its apparent brightness will decrease by a factor of 9.
question
Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do? Determine both the star's distance and luminosity from its apparent brightness. Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity. Calculate the star's surface temperature if we know either its luminosity or its distance. Determine the distance to the star from its apparent brightness.
answer
Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity.
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If star A is closer to us than star B, then Star A's parallax angle is _________. larger than that of Star B fewer parsecs than that of Star B smaller than that of Star B hotter than that of Star B
answer
larger than that of Star B
question
How is the lifetime of a star related to its mass? More massive stars live slightly shorter lives than less massive stars. More massive stars live much longer lives than less massive stars. More massive stars live slightly longer lives than less massive stars. More massive stars live much shorter lives than less massive stars.
answer
More massive stars live much shorter lives than less massive stars.
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What is the common trait of all main sequence stars? They are all spectral type G. They are in the final stage of their lives. They all have approximately the same mass. They generate energy through hydrogen fusion in their core.
answer
They generate energy through hydrogen fusion in their core.
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What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us? It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster's distance. It is the mass of the most massive star in the star cluster, and it tells us the cluster's size. It is the faintest and coldest main sequence star in a cluster, and it tells us the cluster's age.
answer
It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.
question
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore, ________. both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A
answer
both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A
question
Which of the following statements about spectral types of stars is not generally true? The spectral type of a star can be used to determine its color. The spectral type of a star can be used to determine its surface temperature. The spectral type of a star can be used to determine its distance. The spectral type of a star can be determined by identifying lines in its spectrum.
answer
The spectral type of a star can be used to determine its distance.
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Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude? Rigel has a higher surface temperature than Sirius. Rigel has a higher core temperature than Sirius. Sirius has a higher surface temperature than Rigel. Sirius has a higher core temperature than Rigel.
answer
Rigel has a higher surface temperature than Sirius.
question
Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The change in brightness alternates between a small change and a large change. The most likely explanation is that ________. the star is periodically ejecting gas into space, every 73 hours the star is a Cepheid variable the star is a white dwarf the star is a member of an eclipsing binary star system
answer
the star is a member of an eclipsing binary star system
question
The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest? The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs. The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants.
answer
The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.
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Star A has an apparent magnitude of 3, and Star B has an apparent magnitude of 5. Which star is brighter in our sky? Star A Star B The two stars have the same brightness in our sky, but Star A is closer to us than Star B. There is not enough information to answer the question.
answer
Star A
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Our Sun is a star of spectral type ________. G M S F
answer
G
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Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true? Earth would fly off into interstellar space. The supergiant's surface temperature would be much hotter than the surface temperature of our Sun. Earth would be inside the supergiant. The supergiant would appear as large as the full Moon in our sky.
answer
Earth would be inside the supergiant.
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What is a white dwarf? the remains of a star that ran out of fuel for nuclear fusion a type of star that produces energy by gravitational contraction a star that follows a period-luminosity relation a main-sequence star of spectral type F, which tends to look white in color
answer
the remains of a star that ran out of fuel for nuclear fusion
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The faintest star visible to the naked eye has an apparent magnitude of about 0. 1. 6. 10. -1.
answer
6
question
The stellar spectral sequence, in order of decreasing temperature, is OBAGFKM. OBAFGKM. BAGFKMO. OFBAGKM. ABFGKMO.
answer
OBAFGKM.