Star clusters or
star clouds are groups of
stars. Two types of star clusters can be distinguished:
globular clusters are tight groups of hundreds or thousands of very old stars which are
gravitationally bound, while
open clusters, more loosely clustered groups of stars, generally contain fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of
giant molecular clouds as they move through the
galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a
stellar association, sometimes also referred to as a
moving group.