Name: John
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Question:
How much is known about the nearest cluster of stars?
Replies:
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 approx-
imately 300 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 open 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 forces
acting on them." That is why their component stars are young. By contrast,
globular clusters "are much more massive, more tightly packed, more symmet-
rical, and very old. They typically contain 20,000 to several million
stars." The closest is several thousand light-years away.
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