Six Stars Visible, Seven Named

Most people looking at the Pleiades on a clear night count six stars, yet an odd number of traditions, from Greece to Australia, name seven and then tell a story about the one that is missing. The Greeks said the seventh sister hid in shame or grief, and the lost Pleiad became a commonplace of classical poetry, repeated so widely that astronomers have wondered ever since whether one member of the cluster genuinely faded within human memory. Nothing in the modern record settles it: the cluster contains hundreds of stars, and which ones a sharp eye separates depends on darkness, altitude and the observer. What the eye cannot resolve, the telescope reads plainly. The Pleiades are a true open cluster, a family of young hot blue stars that formed together and are still travelling together, some four hundred light years away, wrapped in faint wisps of dust that photographs show as blue reflection nebulosity.

Charles Messier gave the group the forty fifth place in his catalogue, so the cluster carries the designation Messier 45 alongside all its older names. Its brightest member is Alcyone, which this atlas holds as a star in its own right among the fixed stars of the astrological tradition. The tension between what is seen and what is named, six lights and seven sisters, is part of why the cluster has held human attention for as long as records exist.