Messier object

A deep-sky object included in the catalogue compiled by French astronomer Charles Messier. The catalogue contains star clusters, nebulae, and galaxies, not comets.

Deep-sky object: An astronomical object beyond the Solar System that is not an individual star. Messier objects are a famous subset of this broad class.
Charles Messier: An eighteenth-century French astronomer known for compiling a catalogue of non-cometary celestial objects. He observed and published the list that defines Messier objects.
Andromeda Galaxy: The nearest large spiral galaxy to the Milky Way, also designated Messier 31. It is one of the catalogue’s most prominent galaxies.
New General Catalogue: A nineteenth-century catalogue of nebulae, star clusters, and other non-stellar objects compiled by John Louis Emil Dreyer. Its thousands of entries extend far beyond the smaller Messier list.
Open cluster: A loosely bound group of stars formed from the same molecular cloud. Many Messier entries, including the Pleiades, are open clusters.
Comet: A small Solar System body of ice, dust, and rock that can form a coma and tail near the Sun. Messier’s catalogue began as a practical aid for avoiding confusion with comets.
Orion Nebula: A nearby star-forming region in the constellation Orion, also designated Messier 42. Its bright gas and young stars exemplify the catalogue’s nebula entries.
Index Catalogue: Two supplements to the New General Catalogue that list additional nebulae and star clusters. It provides further designations for deep-sky objects absent from Messier’s catalogue.
Globular cluster: A dense, roughly spherical group of old stars bound by gravity. The catalogue includes prominent examples such as Messier 13.
Nebulae and Star Clusters: A 1784 catalogue by William Herschel listing nebulae and star clusters observed with telescopes. Herschel’s later work expanded the systematic cataloguing of fuzzy celestial objects.

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