16. If you know the velocities of the stars in a binary system, but you do
NOT know the distance from the stars to us, which of the following can you
find?
a. the luminosities of the stars
b. the masses of the stars
c. the distance between the stars
d. the radii of the stars
17. How can you tell that the star you are observing is actually an
eclipsing binary?
a. large telescopes reveal stellar disks eclipsing each other
b. the moon eclipses the star at least twice a year
c. sometimes the star appears red, and sometimes it appears blue
d. its brightness varies regularly
18. What is the energy source for a star like the sun?
a. burning a fuel such as coal (combining it with oxygen)
b. gravitational potential energy released by the contraction of the sun
c. nuclear fission of uranium into thorium and helium
d. nuclear fusion of hydrogen into helium
19. Which of the following elements is most common in the sun?
a. carbon
b. uranium
c. hydrogen
d. helium
20. What must you do to fuse two protons?
a. overcome the nuclear force, which makes the protons repel each other
b. collide the protons with two neutrinos, then with each other
c. overcome the electric force, which makes the protons repel each other
d. wait until the gravitational attraction of the protons makes them collide