Parts of the Galaxy

Distinctive populations of stars are found in the various parts of the galaxy.

The thin disk contains metal rich stars which range in age from new born to almost the age of the galaxy. They move in almost circular orbits.

The central bulge contains mostly very old stars, though some star formation is still occurring. Metal abundances range from almost zero to well above the Sun's.

The thick disk contains uniformly old stars with relatively low metal abundances. They move in highly elliptical orbits that are confined to the region of the thick disk.

The halo contains uniformly old stars with low metal abundances. They move in highly elliptical, randomly orientated orbits.

The globular clusters contain the oldest stars in the galaxy. The stars in the disk globulars have moderately low metal abundances. The stars in the halo globulars have very low metal abundances. The disk globulars move in highly elliptical orbits confined to the thick disk region. The halo globulars move through the halo in highly elliptical randomly orientated orbits.