Let us look firstly at open clusters to understand why this is so. Star clusters are particularly important because they allow astronomers to check models of stellar evolution and the ages of stars.

Prominent examples include 47 Tuc, M4 and Omega Centauri although there is some debate as to whether this may in fact be a captured dwarf spheroidal galaxy. Our Milky Way has about 200 globular clusters. The stars within them are not dispersed out of the cluster. Unlike open clusters, globular clusters normally remain gravitationally coherent throughout their lives. The stars are about 10 billion years old so many are red giants or white dwarfs.Īs with open clusters, stars in globular clusters probably had a common origin. The globular cluster 47 Tuc from the ground-based AAT and the HST. Clusters typically contain a few hundred stars though this can vary from as low as a few dozen up to a few thousand. Stars in an open cluster have a common origin - they formed from the same initial giant molecular cloud. They are sometimes called galactic clusters due to their location on the dusty spiral arms on the plane of spiral galaxies. Some examples such as the Hyades and Pleiades are so close that the individual stars can be clearly distinguished by the naked eye. Open clusters are so-named due to the fact that the individual component stars are easily resolved through a telescope. Cluster Ages and Zero-Age Main Sequence.The two basic categories of stellar clusters are open clusters, also known as galactic clusters, and globular clusters. They are are particularly useful to astronomers as they provide a way to study and model stellar evolution and ages. A star cluster is a group of stars that share a common origin and are gravitationally bound for some length of time.