This open cluster contains about 500 stars, in an area that is only 12 light years in diameter. Globular clusters, in contrast, are generally about 12 times larger and can contain over a million stars. Unlike globular clusters, open clusters consist of later-generation stars and are formed inside, not outside, the galactic disk.
M67 is one of the oldest known open clusters (about 10 billion years); because of the clusterΓÇÖs age, its stars are similar in appearance to those in globular clusters. There are, however, subtle differences: open-cluster stars contain greater quantities of heavier elements.
