There are several astronomical catalogues referred to as Nebulae and Star Clusters. A Nebula is a cloud of dust and gas inside a galaxy. Nebulae become visible if the gas glows, or if the cloud reflects starlight or obscures light from more distant objects. The catalogues that it may refer to: Catalogue des nébuleuses et des amas d'étoiles (Messier "M" catalogue) first published 1771 Catalogue of Nebulae and Clusters of Stars (William Herschel 'CN'/"H" catalogue) first published 1786 General Catalogue of Nebulae and Clusters of Stars (John Herschel 'GC'/"h" catalogue) first published 1864 New General Catalogue of Nebulae and Clusters of Stars (Dreyer "NGC" catalogue) first published 1888 Index Catalogue of Nebulae and Clusters of Stars (JLE Dreyer's "IC" catalogue) See also Nebula, a type of celestial body Galaxy, a type of celestial body formerly referred to as nebulae Star cluster or cluster of stars, a type of celestial body Lists of books Astronomical catalogues