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Reading Quiz Chapter 11

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What is the approximate chemical composition (by mass) with which all stars are born?
Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
The total amount of power (in watts, for example) that a star radiates into space is called its _______.
Luminosity
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 9
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
If star A is closer to us than star B, then Star A's parallax angle is _____.
Larger than that of Star B
Ten parsecs is about _______.
32.6 light-years
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
From hottest to coolest, the order of the spectral types of stars is _______.
OBAFGKM (Oh Be A Fine Girl Kiss Me)
Our Sun is a star of spectral type ______.
G
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 a binary sar system.
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?
Spectroscopic binary
The axes on a Hertzsprung-Russell (H-R) diagram represents _____.
Luminosity and surface temperature
What can we infer, at least roughly, from a star's luminosity class?
Its size (radius)
On an H-R diagram, stellar radii ______.
Increase diagonally from the lower left to the upper right
On an H-R diagram, stellar masses _______.
Are impossible to determine
How is the lifetime of a star related to its mass?
More massive stars live much shorer lives than less massive stars
Each choice below lists a spectral type and luminosiy class for a star. Which one is a red supergiant?
Spectral type M2, luminosity class I
What is the common trait of all main sequence stars?
They generate energy through hydrogen fusion in their core.
Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?
Earth would be inside the supergiant
What is a white dwarf?
The remains of a star that ran out of fuel for nuclear fusion
Which of the following statements comparing open and globular star clusters is not true?
Open and globular clusters each typically contain a few hundred stars.
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