Seen edge on. Here is the same picture with names for the parts. We have seen the disk stars in visible and near infrared pictures. We have seen the 21 cm radiation from hydrogen gas in the disk. We have seen the far infrared radiation from dust in the disk.
Some stars are halo stars.
Here is M5 . We first study motion and gravity . Application to the Galaxy. The stars and other matter that make up the Galaxy would just move off into space if it weren't for the gravitational force created by all the mass in the Galaxy. The objects in the disk of the galaxy have orbits in the plane of the disk.