Messier, Charles, meh SYAY, sharl (1730-1817), was a French astronomer. He prepared the first catalog of nonstellar objects visible from the Northern Hemisphere. Such objects include galaxies, nebulae (clouds of dust and gas), and star clusters. Messier began the catalog in the late 1750's and completed it in 1784. His listing, called the Catalogue of Nebulae and of Star Clusters, contains 103 nonstellar objects. Messier discovered most of these objects himself. Astronomers still specify the objects in his catalog by their catalog numbers, placing an M for Messier before the number.