University of Edinburgh

BSL Astronomy Glossary - open cluster - definition

Definition: An Open Cluster is a group of stars that appears as a small fuzzy patch of light in the night sky. Each Open Cluster contains between 100 to 1000 stars, which were created long ago from the same cloud of hydrogen gas (H2). After the hydrogen gas exploded, forming the stars, the stars gradually started to move away from each other creating an Open Cluster.