In astronomy, "IC" stands for Index Catalogue. It's a supplemental catalogue to the New General Catalogue (NGC) that lists additional astronomical objects, primarily nebulae, star clusters, and galaxies, according to several astronomy websitesIn astronomy, "IC" stands for Index Catalogue. It's a supplemental catalogue to the New General Catalogue (NGC) that lists additional astronomical objects, primarily nebulae, star clusters, and galaxies, according to several astronomy websites