Praesepe

Praesepe is not a star at all but a cluster of hundreds of stars, the open cluster known as the Beehive or Messier 44, lying at about 600 light years in the constellation Cancer. To the naked eye it is a faint hazy patch, the ancients called it the Manger, and the two stars flanking it, Asellus Borealis and Asellus Australis, the two Donkeys feeding at it. It is one of the nearest star clusters to the Sun and among the first objects Galileo turned his telescope on, resolving the little cloud into a swarm of separate stars. Its inclusion among the fixed stars of the astrological tradition reflects the old habit of treating any named point of light, cluster or nebula alike, as a star.

Praesepe's status as a genuine open cluster, several hundred stars gravitationally bound together and formed from the same collapsing cloud, was established well before its distance could be measured precisely; modern parallax work places it at almost exactly the same distance and age as the Hyades in Taurus, and the two clusters are now thought to share a common origin, having formed from related material at roughly the same time some six to seven hundred million years ago. Praesepe's designation as Messier 44 places it among Charles Messier's eighteenth-century catalogue of nebulous objects, compiled originally so that comet hunters would not mistake such fixed, non-moving fuzzy patches for a new discovery.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy

Ptolemy in the Tetrabiblos treats the nebulous mass in the breast of Cancer as of the nature of Mars and the Moon, and the tradition that follows gives Praesepe that nature and reads it in a notably grim key, associating this misty cluster above all with the eyes and eyesight, with weak sight and, in the lurid manner of the older sources, with blindness, together with a general reputation for misfortune and disorder. The association of the faint cloud with clouded vision is old and probably owes something to the difficulty of resolving it with the naked eye. It is one of the very few deep-sky objects, rather than single stars, to hold a fixed place in the astrological catalogue.

The Latin name Praesepe, manger, and the two flanking donkeys, Asellus Borealis and Asellus Australis, form a coherent small tableau, the animals feeding at their manger, that is considerably older than the telescope; Ptolemy already describes the "nebulous mass" and its flanking stars in these terms, so the naked-eye picture the name preserves long predates any understanding of what the haze actually was. The blindness and eye-trouble reading Ptolemy attaches to nebulous objects generally recurs for the Pleiades in Taurus elsewhere in this set of tables, part of a single consistent analogical rule rather than a coincidence of two unrelated traditions.