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

The H-R Diagram

9. 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

10. 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