Page "Star cluster" Paragraph 16

Open clusters ( OC ) are very different from globular clusters.

Unlike the spherically distributed globulars, they are confined to the galactic plane, and are almost always found within spiral arms.

They are generally young objects, up to a few tens of millions of years old, with a few rare exceptions as old as a few billion years, such as Messier 67 ( the closest and most observed old open cluster ) for example.

They form from H II regions such as the Orion Nebula.