Reading Quiz Chapter 11 – Flashcards
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What is the approximate chemical composition (by mass) with which all stars are born?
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Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
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The total amount of power (in watts, for example) that a star radiates into space is called its _______.
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Luminosity
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According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
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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?
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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 _____.
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Larger than that of Star B
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Ten parsecs is about _______.
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32.6 light-years
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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?
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Star A
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From hottest to coolest, the order of the spectral types of stars is _______.
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OBAFGKM (Oh Be A Fine Girl Kiss Me)
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Our Sun is a star of spectral type ______.
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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?
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The star is a member of a binary sar system.
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Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
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Spectroscopic binary
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The axes on a Hertzsprung-Russell (H-R) diagram represents _____.
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Luminosity and surface temperature
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What can we infer, at least roughly, from a star's luminosity class?
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Its size (radius)
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On an H-R diagram, stellar radii ______.
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Increase diagonally from the lower left to the upper right
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On an H-R diagram, stellar masses _______.
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Are impossible to determine
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How is the lifetime of a star related to its mass?
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More massive stars live much shorer lives than less massive stars
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Each choice below lists a spectral type and luminosiy class for a star. Which one is a red supergiant?
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Spectral type M2, luminosity class I
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What is the common trait of all main sequence stars?
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They generate energy through hydrogen fusion in their core.
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Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?
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Earth would be inside the supergiant
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What is a white dwarf?
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The remains of a star that ran out of fuel for nuclear fusion
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Which of the following statements comparing open and globular star clusters is not true?
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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?
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It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age
