Astronomy & Astrophysics 101: Open Cluster

What Is an Open Cluster?
Open clusters are loosely bound groups of a few tens to a few hundred stars. They are found in spiral and irregular galaxies.

Open clusters are significantly smaller and less densely populated than globular clusters. Open clusters may contain anything from a few dozen stars up to a few hundred stars. Open clusters have been observed with a range of ages — they may be made up of young stars or older stars.