Question 1

Which of the following best describes the process by which stars generate energy in their cores?

Accepted Answer

Nuclear fusion of hydrogen into helium

Question 2

The luminosity $$L of a $$star is given by the Stefan-Boltzmann law: $$L = 4\pi R^2$ \sigma T^4$. If a star's radius doubles and its temperature triples, by what factor does its luminosity increase?

Accepted Answer

324

Question 3

If two stars have the same luminosity but one appears dimmer than the other from Earth, what is the most likely explanation?

Accepted Answer

The dimmer star is farther away

Question 4

The apparent brightness $$b of a $$star as seen from Earth is related to its luminosity $$L$$ and distance $$r by$$ $$b \propto \frac{L}{r^2$}. If a $$star is moved to twice its original distance, how does its apparent brightness change?

Accepted Answer

It becomes one-fourth as bright

Question 5

Which of the following statements about the magnitude scale is correct?

Accepted Answer

A star with magnitude 6 is 100 times fainter than a star with magnitude 1

Question 6

The color of a star is most closely related to which of the following properties?

Accepted Answer

Its surface temperature

Question 7

Which spectral class corresponds to the hottest stars?

Accepted Answer

O

Question 8

Why do the spectra of stars with similar compositions look different?

Accepted Answer

Because their temperatures are different

Question 9

A brown dwarf is best described as:

Accepted Answer

A failed star that cannot sustain hydrogen fusion

Question 10

Which of the following is NOT a type of binary star system?

Accepted Answer

Optical double

Question 11

The mass-luminosity relation for main sequence stars is approximately $$L \sim M$$^{3.9}$$. If a star has twice the mass of the Sun, what is its luminosity compared to the Sun?

Accepted Answer

About 30 times the Sun's luminosity

Question 12

The H-R diagram plots which two stellar properties against each other?

Accepted Answer

Temperature and luminosity

Question 13

A star's parallax angle is measured to be 0.2 arcseconds. What is its distance in parsecs?

Accepted Answer

$$D = \frac{1}{0.2} = 5$$ parsecs

Question 14

Cepheid variable stars are important in astronomy because:

Accepted Answer

Their period of variability is related to their luminosity

Question 15

Which of the following is true about RR Lyrae stars?

Accepted Answer

They have nearly the same luminosity

Question 16

If a star's spectrum is blue-shifted, what does this indicate about its motion?

Accepted Answer

It is moving toward Earth

Question 17

Which property can be determined by observing the broadening of spectral lines in a star's spectrum?

Accepted Answer

Rotation speed

Question 18

What is the main reason that the spectra of O-type stars show weak hydrogen lines?

Accepted Answer

Hydrogen is mostly ionized at high temperatures

Question 19

Which of the following best describes the method of spectroscopic parallax?

Accepted Answer

Determining a star's distance by using its spectral and luminosity class to estimate luminosity, then comparing to apparent brightness

Question 20

Which of the following statements about the composition of stars is correct?

Accepted Answer

All stars are composed primarily of hydrogen and helium

Stars: Properties, Classification, and Measurement

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