Open Clusters Photo Gallery
An open cluster is a loose collection of stars that formed together from the same interstellar cloud. Thus all the stars in an open cluster are about the same age and distance, and have a similar initial elemental composition. Of course, the masses, temperatures and the stage of stellar evolution can vary considerably from star to star within an open cluster.
The typical open cluster contains several hundred stars that are loosely bound by gravity. Over time, the gravitational tug of outside stars and gas in the galaxy disperse an open cluster within several hundred million years.
Over 1100 open clusters are known in the Milky Way. They are found primarily within the galaxy's disk along with the Sun and the naked-eye stars. We can only see a small fraction (1% to 2%) of the open clusters in the Milky Way since most are hidden behind the intervening gas and dust in other parts of the galaxy.
The 18th-century French astronomer Charles Messier recorded 26 open clusters in his Messier Catalog of deep sky objects. For more information, see the Wikipedia entry about open clusters.
Click on each thumbnail to see a larger image.
