[1] While the Messier catalogue is used by amateur astronomers as a list of deep-sky objects for observation, Moore noted that Messier's list was not compiled for that purpose and excluded many of the sky's brightest deep-sky objects,[1] such as the Hyades, the Double Cluster (NGC 869 and NGC 884), and the Sculptor Galaxy (NGC 253).

Moore also observed that since Messier compiled his list from observations in Paris, it did not include bright deep-sky objects visible in the Southern Hemisphere, such as Omega Centauri, Centaurus A, the Jewel Box, and 47 Tucanae.

Unlike objects in the Messier catalogue, which are listed roughly in the order of discovery by Messier and his colleagues,[5] the Caldwell catalogue is ordered by declination, with C1 being the most northerly and C109 being the most southerly,[1] although two objects (NGC 4244 and the Hyades) are listed out of sequence.

[1] The Caldwell Catalogue has generated controversy in the amateur astronomy community for several reasons.

[6] Caldwell advocates, however, see the catalogue as a useful list of some of the brightest and best known non-Messier deep-sky objects.