Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Which of these forms of radiation passes most easily through the disk of the Milky Way?
(a) red light
(b) blue light
(c) infrared light

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Which part of the galaxy has gas with the hottest average temperature?
(a) the disk
(b) the halo
(c) the bulge

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
How do we determine the Milky Way’s mass outside the Sun’s orbit?
(a) from the Sun’s orbital velocity and its distance from the center of our galaxy
(b) from the orbits of halo stars near the Sun
(c) from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Why do disk stars bob up and down as they orbit the galaxy?
(a) because the gravitational pull of other disk stars always pulls them toward the disk
(b) because of friction with the interstellar medium
(c) because the halo stars keep knocking them back into the disk

Describe the basic characteristics of stars’ orbits in the disk, halo, and bulge of our galaxy.

Use the following questions to check your understanding of what the images show and what we can learn by comparing them.
How do regions showing strong radio emission from molecules look in the visible-light image? Are they bright or are they dark?

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Where are most of the Milky Way’s globular clusters found?
(a) in the disk
(b) in the bulge
(c) in the halo

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
What is the shape of the Milky Way’s halo?
(a) round like a ball
(b) flat like a disk
(c) flat like a disk but with a hole in the center

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
Halo stars orbit the center of our galaxy much faster than the disk stars.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
The star–gas–star cycle will keep the Milky Way looking just as bright in 100 billion years as it looks now.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
If we could watch a time-lapse movie of a spiral galaxy over millions of years, we’d see many stars being born and dying within the spiral arms.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
We know that a black hole lies at our galaxy’s center because numerous stars near it have vanished over the past several years, telling us that they’ve been sucked in.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
The Sun’s velocity around the Milky Way tells us that most of our galaxy’s dark matter lies near the center of the galactic disk.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
The carbon in my diamond ring was once part of interstellar dust grains.