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Globular cluster Messier 75 (M75, NGC 6864) is one of the apparently fainter globular clusters in Messier's catalog, due to its large distance. It is situated in the eastern part of Sagittarius.
After its discovery in the night of August 27-28, 1780 by Pierre Méchain, globular cluster M75 was observed by Charles Messier on October 5 and October 18, 1780, and added to his catalog after obtaining a position. William Herschel resolved it into stars in 1784 and described it as a "miniature of M3."
At a distance of about 67,500 light years, M75 is one of the more remote of Messier's globular clusters, lying well beyond the Galactic center (from which it is 47,600 light years distant). Some sources give even larger distances, up to as much as 100,000 light years ! (E.g., Burnham has 95,000) This would make it the most remote Messier globular, and the most remote galactic Messier object at all. But W.E. Harris' database has it with 67,500 light years.
M75 is one of the more compact, concentrated globulars, classified as class I. Because of this and its distance, larger scopes are required to resolve it into stars. Its angular diameter of 6.6' corresponds to a linear extension of well almost 130 light years, and it is of high luminosity, perhaps about 180,000 times that of the Sun
