catalog, descriptive list, on cards or in a book, of the contents of a library. Assurbanipal's library at Nineveh was cataloged on shelves of slate. The first known subject catalog was compiled by Callimachus at the Alexandrian Library in the 3d cent. B.C. The library at Pergamum also had a catalog. Early in the 9th cent. A.D. the catalogs of the libraries of the monastery at Reichenau and of the abbey at Saint-Riquier, N France, included summaries of the works cataloged. In 1472 the monastic library at Clairvaux was recataloged and one of the earliest union catalogs was made—of the contents of 160 Franciscan monastery libraries in England. In 1475 the Vatican librarian, Platina, cataloged that library's 2,527 volumes. About 1660 Clement, librarian of the Bibliothèque du Roi under Louis XIV, compiled a subject catalog and inventory of manuscripts. The printing of the British Museum catalog was begun by Panizzi as keeper (1837-56) of printed books. Charles A. Cutter devised the modern dictionary catalog (with author, title, and subject arranged in one alphabet) for the Boston Athenaeum library. Melvil Dewey devised his decimal system in the 1870s; the system was widely applied in smaller libraries and many large ones. In 1901 the Library of Congress began the practice of printing its catalog entries on cards 3 by 5 in. (7.6 by 12.7 cm) and distributing them to other libraries for a small fee. The National Union Catalogue, begun in 1952 by the Library of Congress, collated the card catalog entries of the larger American libraries and printed the results in book form. The advent of the computer has dramatically expanded the ability of libraries to provide extensive bibliographic services. By consulting an electronic catalog, such as the WorldCat of the OCLC Online Computer Library Center, a person can access more than 35 million catalog records in some 25,000 libraries around the world.

New General Catalog (NGC), standard reference list of nebulae (see nebula). It is based on the General Catalog, published in 1864, which included 2,500 nebulae cataloged by William Herschel and an additional 2,500 cataloged by his son, John Herschel. The General Catalog was combined with work of other observers and the resulting total of more than 7,800 entries was published as the New General Catalog of Nebulae by J. Dreyer in 1888. This work was updated by publication of two Index Catalogs (IC), in 1895 and 1910. More than 13,000 objects are listed in these works, of which more than 12,000 are extragalactic nebulae (galaxies). Some nebulae listed in the NGC are also listed in the Messier catalog, e.g., the Andromeda Galaxy is listed both as NGC 224 and as M31.

Messier catalog, systematic list of nebulae and star clusters. A first list, compiled and published in 1771 by Charles Messier, contained 45 objects. The final list, published in 1784, contained 103 objects; some of these were later removed from the list. Of the remaining objects, about 50 are extragalactic nebulae, i.e., galaxies. Designations from Messier's catalog are frequently used to refer to the brighter nebulae and star clusters; for example, M31 is the Andromeda Galaxy, M1 the Crab Nebula, M42 the Great Nebula in Orion, and M45 the Pleiades.

List of about 109 star clusters, nebulae, and galaxies compiled by the French astronomer Charles Messier (1730–1817), who discovered many of them. Still a valuable guide to amateur astronomers, it was superseded by the New General Catalogue (NGC); both NGC and M reference numbers remain in common use.

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