Date: 1993 - 1999
How much is known about the nearest cluster of stars?
According to the text "Astronomy: the Cosmic Journey" by Wm. Hartmann,
the closest open cluster is the Ursa Major cluster, centered about 22 parsecs
(about 72 light years) away. This cluster contains (among others) most but not
all of the stars that make up the Big Dipper. Its total mass is approximately 30 0 solar masses and
it is about 200 million years old. It is a fairly typical loose open cluster.
There are about 900 open clusters in the Milky Way, concentrated in the plane of
the galaxy. Typically they contain 100 to 1000 members. The text says "...most o pen clusters have
prominent young stars or associated clouds of star-spawning gas." Stars
generally form in open clusters, but "most such clusters break apart into
individual stars within only a few hundred million years because of dynamic forc es acting on them." That's
why their component stars are young. By contrast, globular clusters "are much
more massive, more tightly packed, more symmetrical, and very old...They
typically contain 20,000 to several million stars." The closest is several thous and light-years away.
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Update: June 2012