Like the Messier Catalog, The Caldwell Catalogue is an astronomical index of 109 star clusters, nebulae, and galaxies for observation by amateur astronomers. The list was compiled by Patrick Moore to enhance to observable objects listed in the Messier catalogue, which was originally created to discern these deep-space objects from comets.
The Caldwell Catalogue also includes bright deep-sky objects visible in the Southern Hemisphere, such as Omega Centauri, Centaurus A, the Jewel Box, and 47 Tucanae, not found in the Messier collection which only focused on the Northern Hemisphere.
The objects Caldwell catalogue are listed by declination, with C1 being the most northerly and C109 being the most southerly.
The Caldwell catalogue was published in December 1995, making it a more contemporary listing than the Messier Catalog created in the late 1700s. The advancements in optics made the observable celestial space much more resolvable.
The items referenced in the Caldwell Catalog can also be found by their NGC (New General Catalog) numbers.
Like the Messier chasers, there are astronomers that seek to observe or photograph all 109 Caldwell Catalogue objects.