The Ursa Major Cluster (also known as Collinder 285)
comprises the central part of the
Big Dipper, itself a part of
Ursa Major, the Greater Bear. The major stars
in the picture are, from left to right,
Dubhe (which is
not part of the cluster),
Merak, Phecda,
Megrez, Alioth,
and Mizar. Alcor, next
to Mizar, is a member as well, as are several other stars in the picture.
Averaging 80 light years away, 250 to 500 million years old,
the cluster sprawls over a line
some 30 light years long. It is at the heart of the much larger Ursa Major Stream,
or Moving Group.
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