A young family of a few dozen stars formed simultaneously and still physically close together, sometimes called a galactic cluster. There are around 1000 open clusters in our Milky Way galaxy alone, the Pleiades being the one most readily visible to the naked eye.

The nearest open cluster is actually the Big Dipper, a well known asterism which is the tail of the constellation Ursa Major (or the Big Bear).

An open cluster is characterized by the fact that the stars are not gravitationally bound. Although the stars in an open cluster are believed to have formed together, they will eventually separate due to the rotation of the Milky Way.

Some open clusters (such as M11 in Scutum, or the double cluster in Perseus) have about 1,000 stars in them.

The Orion Nebula (the brightest nebula in the sky, located within his 'sword') is still such a 'star nursery', and even a pair of binoculars will allow one to see the illuminated dust and gas which surround the young stars at its center.

Another nearby open cluster, conveniently located almost exactly halfway between Orion and the Pleiades, looking at the sky, are the Hyades, which are the 'V' formed by the face of the constellation Taurus. The bright red star Aldebaran is at one corner - the bull's eye - though it is not actually in the cluster.

The Hyades are about twice as far from the solar system as the Big Dipper, and the Plieades are about 3 times further away than the Hyades. Similarly, the Orion association of stars (the nebula, as well as the stars of his 'belt') are about twice as far away, again.

Of these 4 clusters, the densest group is the Big Dipper. It's only becuase of greater distance from us, that the others appear to be more closely knit.

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