Review

#01

We see a milky band that stretches across the night sky. There are more stars in this band than elsewhere in the sky.

#02

The dust in the interstellar medium significantly restricts our view of our galaxy.

#04

Halo.

#05

25 Mpc.

#09

Disk star orbit in nearly circular orbits, all in the same direction, and in the disk (of course). The orbits of halo stars can be quite elliptical, that are prograde or retrograde, and which are highly inclined to the disk.

#10

We can map out the arms, by looking at where OB stars live, and using radio observations to locate cold clouds of H gas.

#13

Refers to the case when the action of star formation itself triggers a subsequent star formation event, and this continues over and over again.

#19

There is too much dust to view the galactic center in the optical band.

#20

Radio, infrared, and X-rays, because the galaxy is far more transparent at the wavelengths.