Caldwell Objects

Caldwell Objects

The Caldwell Catalogue is an astronomical catalog of 109 bright star clusters, nebulae, and galaxies for observation by amateur astronomers. The list was compiled by Sir Patrick Caldwell-Moore, better known as Patrick Moore, as a complement to the Messier Catalogue.

The Messier Catalogue is used frequently by amateur astronomers as a list of interesting deep-sky objects for observations, but Moore noted that the list did not include many of the sky's brightest deep-sky objects, including the Hyades, the Double Cluster (NGC 869 and NGC 884), and NGC 253. Moreover, Moore observed that the Messier Catalogue, which was compiled based on observations in the Northern Hemisphere, excluded bright deep-sky objects visible in the Southern Hemisphere such as Omega Centauri, Centaurus A, the Jewel Box, and 47 Tucanae. He quickly compiled a list of 109 objects (to match the number of objects in the Messier Catalogue) and published it in Sky & Telescope in December 1995.

Since its publication, the catalogue has grown in popularity and usage within the amateur astronomical community. Small compilation errors in the original 1995 version of the list have since been corrected. Moore used his other surname to name the list as M for Moore was already taken by Messier, and the catalogue adopts "C" numbers to rename objects with more common designations.

As stated above, the list was compiled from objects already identified by professional astronomers and commonly observed by amateur astronomers. Unlike objects in the Messier catalogue, which are listed in the order they were discovered, the Caldwell catalogue is ordered by declination, with C1 being the most northerly and C109 being the most southerly, although two objects (NGC 4244 and the Hyades) are listed out of sequence. The original list also incorrectly identified S Norma Cluster (NGC 6087) as NGC 6067 and incorrectly labelled the Lambda Centauri Cluster (IC 2944) as the Gamma Centauri Cluster.

A natural progression for the amateur astronomer wishing to observe deep sky objects would be to view the Messier catalogue, followed by the Caldwell catalogue, and then the Herschel 400 Catalogue. At the end of this exercise the observer would have viewed nearly 600 objects. Although there are 618 objects listed in these three catalogues the Herschel 400 Catalogue does contain some objects from the Messier and Caldwell catalogues.