6. The wavelength of blue light is about half that of red light. The frequency of blue light is ______________ that of red light, and the energy of a blue light photon is ______________ that of a red light photon.
a. half, half
b. two times, four times
c. two times, two times
d. four times, four times

7. The Keck telescope has four times the diameter of the Hubble Space Telescope. Ignoring the effects of Earth's atmosphere, the Keck telescope has _____________ angular resolution and _____________ the light-collecting power of the Hubble Space Telescope.
a. one fourth as good; one sixteenth
b. one half as good; four times
c. four times better; sixteen times
d. four times better; four times

8. Mars orbits the sun at a distance of approximately 1.5 AU. What is its orbital period in years?
a. the cube root of 1.5, which is about 1.14
b. the square root of 1.5, which is about 1.22
c. the cube root of 1.5 squared, which is about 1.31
d. the square root of 1.5 cubed, which is about 1.84

9. Proxima Centauri, the nearest star to the sun, is a Main Sequence star that is cooler 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

For questions 10, 11, and 12: Alpha Centauri is a binary, consisting of two Main Sequence stars, Alpha Centauri A and Alpha Centauri B. Alpha Centauri A is a one-solar-mass star, and Alpha Centauri B is a one-half-solar-mass star. They are separated by about 10 AU, the distance between the sun and Saturn.

10. Alpha Centauri A is yellow. What color is Alpha Centauri B?
a. orange
b. yellow
c. blue
d. a one-half-solar-mass star is too cool to fuse hydrogen, so it doesn't emit any visible light

11. Alpha Centauri A takes 30 years to orbit the binary's center of mass. How long does Alpha Centauri B take to orbit the center of mass?
a. 15 years
b. 30 years
c. 60 years
d. 900 years