Chapter 12 Reading Quiz

What is the approximate chemical composition (by mass) with which all stars are born?

a.) three quarters hydrogen, one quarter helium, no more than about 2% heavier elements
b.) half hydrogen and half helium
c.) 95% hydrogen, 4% helium, no more than 1% heavier elements
d.) 98% hydrogen, 2% helium

a.) 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 _________.

a.) apparent brightness
b.) luminosity
c.) absolute magnitude
d.) flux

b.) luminosity

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

a.) Its apparent brightness will decrease by a factor of 3.
b.) Its apparent brightness will increase by a factor of 9.
c.) Its apparent brightness will decrease by a factor of 9.
d.) Its apparent brightness will increase by a factor of 3.

c.) 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?

a.) Determine both the star’s distance and luminosity from its apparent brightness.
b.) Calculate the star’s surface temperature if we know either its luminosity or its distance.
c.) Determine the distance to the star from its apparent brightness.
d.) Calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity.

d.) 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 _________.

a.) larger than that of Star B
b.) smaller than that of Star B
c.) hotter than that of Star B
d.) fewer parsecs than that of Star B

a.) larger than that of Star B

Ten parsecs is about _________.

a.) 150 million kilometers
b.) 10 parallax seconds of angle
c.) 32.6 light-years
d.) 10,000 seconds

c.) 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?

a.) There is not enough information to answer the question.
b.) The two stars have the same brightness in our sky, but Star A is closer to us than Star B.
c.) Star A
d.) Star B

c.) Star A

From hottest to coolest, the order of the spectral types of stars is _________.

a.) OMKGFBA
b.) ABCDEFG
c.) ABFGKMO
d.) OBAFGKM
e.) OBAGFKM

d.) OBAFGKM

Our Sun is a star of spectral type _________.

a.) M
b.) F
c.) G
d.) S

c.) 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?

a.) The star is of spectral type A.
b.) The star is a member of a binary star system.
c.) The star is of spectral type G.
d.) We know the star’s luminosity and distance.

b.) 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?

a.) eclipsing binary
b.) spectroscopic binary
c.) visual binary
d.) double star

b.) spectroscopic binary

The axes on a Hertzsprung-Russell (H-R) diagram represent _________.

a.) mass and luminosity
b.) mass and radius
c.) luminosity and surface temperature
d.) luminosity and apparent brightness

c.) luminosity and surface temperature

What can we infer, at least roughly, from a star’s luminosity class?

a.) its age in years
b.) its size (radius)
c.) its mass
d.) its surface temperature

b.) its size (radius)

On an H-R diagram, stellar radii _________.

a.) increase diagonally from the lower left to the upper right
b.) decrease from left to right
c.) are impossible to determine
d.) are greatest in the lower left and least in the upper right

a.) increase diagonally from the lower left to the upper right

On an H-R diagram, stellar masses _________.

a.) are impossible to determine
b.) can be determined for main sequence stars but not for other types of stars
c.) decrease from upper left to lower right
d.) are greatest in the lower left and least in the upper right

b.) can be determined for main sequence stars but not for other types of stars

How is the lifetime of a star related to its mass?

a.) More massive stars live slightly longer lives than less massive stars.
b.) More massive stars live much shorter lives than less massive stars.
c.) More massive stars live much longer lives than less massive stars.
d.) More massive stars live slightly shorter lives than less massive stars.

b.) More massive stars live much shorter lives than less massive stars.

Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?

a.) Spectral type G2, luminosity class V
b.) Spectral type M2, luminosity class I
c.) Spectral type M1, luminosity class V
d.) Spectral type O9, luminosity class I

b.) Spectral type M2, luminosity class I

What is the common trait of all main sequence stars?

a.) They are in the final stage of their lives.
b.) They generate energy through hydrogen fusion in their core.
c.) They are all spectral type G.
d.) They all have approximately the same mass.

b.) 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?

a.) The supergiant would appear as large as the full Moon in our sky.
b.) Earth would be inside the supergiant.
c.) The supergiant’s surface temperature would be much hotter than the surface temperature of our Sun.
c.) Earth would fly off into interstellar space.

b.) Earth would be inside the supergiant.

What is a white dwarf?

a.) It is a star that follows a period-luminosity relation.
b.) a main sequence star of spectral type F, which tends to look white in color
c.) is a type of star that produces energy by gravitational contraction.
d.) the remains of a star that ran out of fuel for nuclear fusion

d.) 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?

a.) Stars in open clusters are relatively young while stars in globular clusters are very old.
b.) For both open and globular clusters, we can assume that all the stars in a particular cluster are about the same age.
c.) Open clusters are found only in the disk of the galaxy while globular clusters may be found both in the disk and the halo of the galaxy.
d.) Open and globular clusters each typically contain a few hundred stars.

d.) 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?

a.) It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster’s age.
b.) It is the luminosity class of the largest star in a star cluster, and it tells us the cluster’s age.
c.) It is the mass of the most massive star in the star cluster, and it tells us the cluster’s size.
d.) It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster’s distance.

a.) It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster’s age.