The Pleiades are among those objects which are known since the earliest times. At least 6 member stars are visible to the naked eye, while under moderate conditions this number increases to 9, and under clear dark skies jumps up to more than a dozen.  Modern observing methods have revealed that at least about 500 mostly faint stars belong to the Pleiades star cluster.  This image, which was taken by David Malin with the UK Schmidt Telescope, is copyrighted by the Royal Observatory Edinburgh and the Anglo-Australian Observatory. 

The Pleiades also carry the name "Seven Sisters".   According to Greek mythology, the main, visible stars are named for the seven daughters of "father" Atlas and "mother" Pleione: Alcyone, Asterope (a double star), Electra, Maia, Merope, Taygeta and Celaeno. 

This information was taken from the The Messier Catalog web site, which descries over 100 diffuse astronomical objects that are not planets, comets, or single stars.  Though Charles Messier did not know what these objects were when he described them in the 19th century, we have now discovered that these objects are beautiful nebulae, star clusters, and galaxies.