hat is the approximate chemical composition (by mass) with which all stars are b |
Three-quarters hydrogen, one-quarter helium, no more than about 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 |
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 star system.The star is a member of a binary star 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 represent _________. |
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 _________. |
can be determined for main-sequence stars but not for other types of stars |
More massive stars have __________ lives than less massive stars. |
much shorter |
Each choice that follows lists a spectral type and luminosity 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. |
All stars are born with the same basic composition, yet stars can differ greatly in appearance. Which two factors are most important in determining the current appearance of a star? |
Mass and stage of life |
Which units are appropriate for measurement of apparent brightness? |
Watts per square meter |
Star A is identical to Star B, but 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 |
A star with a parallax angle of 1/20 arcsecond is _________. |
20 parsecs away |
A star’s color is related to it’s surface temperature because _________. |
stars emit thermal radiation |
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 distance. |
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. |
To calculate the masses of stars in a binary system, we must measure their _________. |
orbital period and average orbital distance |
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 significantly dimmer for about 2 hours. The most likely explanation is that _________. |
the star is a member of an eclipsing binary star system |
You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star’s _________. |
mass |
The approximate main-sequence lifetime of a star of spectral type O is _________. |
3 million years |
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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Astronomy Chapter 12
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