Note: The word "brightness" is used in this quiz to mean how bright a star appears in the sky. The word "luminosity" refers to how bright a star is (independent of its distance from us).
1.What happens when a stationary observer views a moving light
source?
a. the speed, frequency, and wavelength of the light all change
b. the frequency of the light doesn't change, but its wavelength and
speed do
c. the speed of the light doesn't change, but its frequency and wavelength
do
d. the wavelength and brightness of the light change, and the speed and
frequency stay the same
2. Because of the Doppler shift, a light source emits light that is
_________ when it is moving ____________ than when it is at rest.
a. redshifted (at longer wavelengths); away from us
b. redshifted (at longer wavelengths); across our line of sight
c. redshifted (at longer wavelengths); toward us
d. blueshifted (at shorter wavelengths); in any direction
3. What is a parsec?
a. a unit of time equal to about 3.26 million seconds
b. a unit of angle equal to 1/3600 of a degree
c. the distance light travels in one year
d. the distance at which the parallax angle is 1 arcsecond
4. The trigonometric parallaxes of Stars A and B are measured. Star A has
a parallax angle of 1 arcsecond, and Star B has a parallax angle of 0.5
arcsecond. Which of the following is true?
a. Star A is twice as far away as Star B
b. Star B is twice as far away as Star A
c. Star A is twice as large as Star B
d. Star B is twice as large as Star A
5. We move two stars, Vega and the sun, so that both are 10 parsecs from
Earth. We find that Vega's magnitude is 0 (zero), and the sun's is +5.
Now move the stars back to their original places. Suppose that Vega has
a planet orbiting it at a distance of 1 AU. How bright will Vega appear
from that planet?
a. 100 times as bright as the sun
b. 5 times as bright as the sun
c. 1/5 as bright as the sun
d. 1/100 as bright as the sun
6. What do you need to know to determine a star's luminosity?
a. brightness and color
b. brightness and distance
c. color and distance
d. distance and radius
7. Why do hot O stars have weaker hydrogen lines in their visible-light
spectra than cooler A stars do?
a. O stars contain a lower percentage of hydrogen than A stars
b. The hydrogen in O stars' atmospheres is all in the ground state,
and absorption lines starting from the ground state aren't in the visible
c. O stars do have hydrogen lines in the visible, but they're emission lines
d. Most hydrogen atoms in O stars are ionized, so they can't absorb photons
9. The star Spica is hotter and more luminous than the sun. Where on the
H-R diagram would it be found?
a. above and to the right of the sun
b. above and to the left of the sun
c. below and to the right of the sun
d. below and to the left of the sun
10. What is the Main Sequence on the H-R diagram?
a. the clump of stars in the upper right part of the diagram
b. the clump of stars in the lower left part of the diagram
c. the diagonal line running from the top left to bottom right
d. all the stars brighter than the sun
11. Which of the following is the mass and luminosity of a possible Main
Sequence star?
a. mass = 1 solar mass, luminosity = 10 solar luminosities
b. mass = 2 solar masses, luminosity = 11 solar luminosities
c. mass = 2 solar masses, luminosity = 0.5 solar luminosities
d. mass = 10 solar masses, luminosity = 1 solar luminosity
12. The star Capella is the same color as the sun, but it is much more
luminous. What can be inferred from this?
a. Capella is bigger than the sun and has a lower surface temperature
b. Capella is bigger than the sun and has a higher surface temperature
c. Capella is smaller than the sun and has the same surface temperature
d. Capella is bigger than the sun and has the same surface temperature
13. Stars A and B are the same size. The temperature of Star A is twice
the temperature of Star B. Which of the following is true?
a. Stars A and B have the same luminosity
b. Star A is twice as luminous as Star B
c. Star A is 4 times as luminous as Star B
d. Star A is 16 (24) times as luminous as Star B
For questions 14 and 15: Sirius A is twice as massive as its white dwarf companion, Sirius B.
14. The equation for the location of the center of mass is
M1*R1 = M2*R2.
Where is their center of mass?
a. at the center of Sirius A
b. halfway between Sirius A and Sirius B
c. between the two stars, but closer to Sirius A
d. between the two stars, but closer to Sirius B
15. The orbital period of Sirius B is 50 years. What is the orbital period
of Sirius A?
a. 25 years
b. 50 years
c. 100 years
d. 200 years
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