Messier 45 or as it is often called, The Pleiades. The name is possibly derived from ancient Greek word "plein" meaning to sail. It is often called the Seven Sisters as the brightest stars are named for the Greek mythological sisters of Atlas and Pleione, Alcyone, Electra, Maia, Merope, Taygeta, Celaeno, and Asterope or Sterope.
The reflection nebula around the cluster was originally thought to be left over dust from the clusters formation, but due to the age of the cluster, that nebulosity would have been dispersed. It seems it is just passing through an dusty region.
The cluster is an estimated 444 light years away, contains over 1,000 members and a large number of brown dwarf objects. Like most clusters, it will slowly disperse over millions of years. The cluster's age is estimated to be between 75 and 150 million years old.