Pleiades

The Pleiades is a group of the seven prominent stars that has been recognized for millennia. Though extremely recognizable and well-known, the grouping is much smaller than a constellation, thus can be termed an asterism. These are now known to be seven B-type stars of an open cluster (named the Pleiades) which consists 1000+ stars in all. The cluster is thought to be on the order of 100 million years old.