Utah Skies: Star Clusters
High concentrations of stars viewed in binoculars or a telescope are always exciting to see. These sometimes appear as star clusters. There are two main types of star clusters—open clusters and globular clusters.
Open clusters are groups of stars that are usually very young stars, most less than a billion years old. They may have a few hundred stars in the cluster, and they are usually confined to the galactic plane of the galaxy. Most of what we will view with our binoculars or telescope is within the Milky Way. Pleiades, the Seven Sisters, is an open cluster. Visually, most people can see seven stars. However, there are more than 800 stars in this cluster. In binoculars, it is easy to identify more than 30 stars.
Globular clusters range from 10,000 to several million stars. Those in the Milky Way are outside the galactic plane in the halo region of the galaxy. If you think of the galaxy as a dish, they are above and below the dish. They are normally made up of very old stars, some of these stars formed almost 13 billion years ago. Our galaxy has more than 100 globular custers. Some of these may have been captured, as a result of mergers between the Milky Way Galaxy and other galaxies. The Hercules Cluster, Messier Object M13, is very bright and easy to see in binoculars or a telescope. It has several hundred thousand stars on it. Another is the Messier Object M22 in Sagittarius. It has 70,000 stars.
In dark skies, it is easy to see several of these clusters. A printed star chart or an app on a cell phone can help you find many of these objects. They are beautiful to see with binoculars or telescopes.