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 6540
NGC 6540 is a globular cluster of stars in the souther constellation Sagittarius, positioned about 4.66° away from the Galactic Center. It was discovered by German-British astronomer Wilhelm Herschel on May 24, 1784, with an 18.7-inch mirror telescope, who described the cluster as "pretty faint, not large, crookedly extended, easily resolvable". It has an apparent visual magnitude of 9.3 with an angular diameter of about 9.5 arcminutes. The cluster is located at a distance of 12 kly (3.7 kpc) from the Sun, and 14 kly (4.4 kpc) from the Galactic Center. It was originally thought to be an open cluster before being designated a globular. The cluster includes a peculiar X-ray source of uncertain type.
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Wikipedia Page: NGC 6540
NGC 6540 at In-The-Sky website