Section 14.C More on Motions in the Galaxy

Question 1

Realize the galaxy, like the Sun and some layers of the Earth, rotates ______, not like a solid object, so further stars _____ make the same progress around the galaxy as do stars closer to the center. They _____ other stars that are closer to the center

Answer 1

• differentially
• do not
• lag behind

Question 2

the correct time it takes for the Sun to orbit our galaxy

Answer 2

225 million years

Question 3

Identify _______ as being waves of density or crowding material in the galaxy. It is similar to a weather front or a traffic jam. Clouds of gas and dust get squeezed together in the wave and this can lead the clouds to make what kind of objects?

Answer 3

• spiral arms or spiral density waves

Question 4

The reason spiral arms shine brightest: They have younger stars, which means the short-lived heavy stars are there.

Answer 4

• Those stars can glow millions of times brighter than the Sun, so it only takes a few to make the spiral arms bright.
• The arms do NOT contain a lot more stars total than the rest of the galaxy.