A Star Cluster is a group of stars with many different masses
that were all formed (born) at the same time, from the same Giant
Molecular Cloud, and have continued to live together. Open
Star Clusters are some of the youngest groups of stars in our
galaxy, and consist of several hundred to several thousand stars.
The following are pictures of Open Star Clusters, roughly in
order of age; from youngest to oldest. The first few are still
embedded in the dust and gas they were forming out of. The youngest
clusters contain many massive, O- and B-type (blue colored) stars,
these stars evolve faster than lower mass stars so they are the first
ones in a cluster to "die". The last cluster has lost most
of these hot, blue stars, which have evolved to become Giant
stars (seen as bright yellow, orange, and red colored stars).
