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, such as the Hyades, the Double Cluster (NGC 869 and NGC 884), and the Sculptor Galaxy (NGC 253). The Messier catalogue was actually compiled as a list of known objects that might be confused with comets.
The Messier catalogue is commonly employed by amateur astronomers as a resource for observing deep-sky objects; however, its origins reveal that it was not designed with this purpose in mind. Rather, the catalogue's creator, Messier, compiled it to identify potential comet impostors, thereby excluding many notable deep-sky objects like the Hyades and the Double Cluster.