Although some stars travel alone in galaxies, most are grouped in star clusters.
There are two types of star clusters, open clusters and globular clusters.
Open clusters contain between 10 and 10,000 stars loosely distributed over 15 to 40 light-years.
Most of the stars are relatively young, bright, and hot.
Open clusters appear within the galactic plane, the nucleus and spiral arms.
Globular clusters have between 100,000 and 1 million stars, densely packed within the space of 75 to 400 light-years.
There are only about 150 globular clusters in the Milky Way and they inhabit a spherical region around the galaxy called the galactic halo.
Stars in the globular clusters are some of the oldest stars discovered in the galaxy.
