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What is the approximate chemical compositon with which all stars are born?
Three quarters hydrogen, one quarter helium, and no more than 2% heavier elements.
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The total amount of power that a star radiates into space is called its _____.
Luminosity.
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According to the invers 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 9.
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Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?
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 Sta A's parallax angle is _____.
Larger than that of Star B
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Ten parsecs is about _____.
32.6 light-years.
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Star A has and apparent magnitude of 3 and star B has an apparent magnitude of 5. Which star is brighter in our sky?
Star A.
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From hottest to Coolest, the order of the spectral types of stars is _____.
OBAFGKM
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OUr Sun is a star of spectral type_____.
G.
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Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
The star is a member of the binary star system.
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What term is given to a pair of stars that we can determine are orbitiong each other only by measuring their periodic Doppler shifts?
Spectroscopic binary.
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The axes on a Hertzsprung-Russell diagram represent _____.
Luminosity and surface temperature.
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What can we infer, at least roughly, from a star's luminosity class?
Its size.
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On an H-R diagram, stellar radii _____.
Increase diagonally from the lower left to the upper right.
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On an H-R diagram, stellar masses _____.
Can be determined for main sequence stars but not for other types of stars.
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How is the lifetime of a star related to its mass?
More massive stars live much shorter lives than less massive stars.
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What spectral type and luminosity is a red supergiant?
Spectral type M2, luminosity class I.
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What is the common trait of all main sequence stars?
They generate energy through hydrogen fusion in their core.
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Suppose our Sun were suddenly replaced by a supergiant star. What would be true?
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.
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What statement comparing open and globular star clusters is not true?
Open and globular clusters each typically contain a few hundred stars.
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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.
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All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?
Its mass and its stage of life.
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Based on the definition of apparent brightness, which units are appropriate for its measurements?
Watts per square meter.
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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 luminosity, but the apparent brightness of Star B is four times that of Star A.
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A star with a parallax angle of 1/20 arcsecond is _____.
20 parsecs away.
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The star Vega has an absolute magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that _____.
Vega is nearer than 10 parsecs from Earth.
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What statement about spectral types of stars is not generally true?
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 star and Rigel is a star with spectral type B star. What can we conclude?
Rigel has a higher surface temperature than Sirius.
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To calculate the masses of stars ina binary system, we must measure their_____.
Orbital period and average orbital distance.
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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 most likely explanation is that _____.
The star is a member of an ecliosing binary star system.
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You observe a star and you want to plot it on an H-R ndiagram. You will need not measure the star's _____.
Mass.
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The approximate main-sequence lifetime of a star of spectral type O is _____.
3 million years.
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How did astronomers discover the relationship between spectral type and mass for main sequence stars?
by measuring the masses and spectral types of main-sequence stars in binary systems.
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What describes the youngest star cluster on the H-R diagram?
The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.
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On the H-R diagram, which cluster is most likely to be located in the halo of our galaxy?
The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.
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