The New General Catalogue of Nebulae and Clusters of Stars (abbreviated as NGC) is a catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, known as the NGC objects. It is one of the largest comprehensive catalogues, as it includes all types of deep space objects, including galaxies, star clusters, emission nebulae and absorption nebulae.
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NGC 6331
NGC 6331 is a type E elliptical galaxy located in the Ursa Minor constellation. It is located 737 million light-years from the Solar System and was discovered by German-British astronomer William Herschel on December 20, 1797, utilizing an 18.7-inch f/13 spectrum telescope but also observed by Guillaume Bigourdan. With an approximate diameter of 345,000 light-years, NGC 6331 is well considered one of the largest galaxies. It is the brightest group member of Abell 2256 and first in 6' string to the east, making up of 6 galaxies. NGC 6331 also makes up a part of the galactic triplet CGCG 355-024 which comprises two other elliptical galaxies in the cluster, CGCG 355-024 NED03 (PGC 59513) and CGCG 355-024 NED01 (PGC 84827).
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Wikipedia Page: NGC 6331
NGC 6331 at In-The-Sky website