Messier Catalogue

A catalogue of about a hundred of the brightest galaxies, star clusters and nebulae, compiled by the French astronomer Charles Messier (1730-1817). His initial list, published in 1774, contained 45 objects but it was supplemented later with additional discoveries and contributions from Messier's colleague, Pierre Méchain. Objects in the catalogue, which is still widely used, are identified by the prefix "M" and their catalogue number. The list was not compiled systematically. Messier's prime interest was searching for comets, and he noted hazy objects spotted during comet searches. Some were first recorded by Messier, but others were already known. There are some errors and discrepancies in the list as published. M40 is a double star and M73 a group of four stars, but not a true cluster. The identification of M91 is uncertain from the original source, and M102 was a duplication of M101. Messier's own list stopped at number 103 but a further seven have been added in the twentieth century.