- M 73 (NGC 6994)
M 73 is an object that Charles Messier included in his list as a result of observations on the night of the 4th of October, 1780. On that night, he was looking to confirm his colleague's (Pierre Mechain) previous observation of the nearby M 72 in the constellation Aquarius, an object we now know as a globular cluster. He came across a "cluster of three or four faint stars, which resembles a nebula at first glance, contains some nebulosity." Modern observations reveal no nebulosity, but a small grouping of four faint stars (as evident in my image). The visual magnitudes of the stars are 10.5, 11.3, 11.9 and 11.9. So, is M 73 a sparse open cluster, the remains of a old open cluster, or just a chance alignment of physically unrelated stars? Recent observations give the distances to the four stars (in the order of their magnitudes) as 2590, 1080, 900 and 2475 LY. Based on these distances, it is apparent that the four stars are physically unrelated. So, M 73 is just an asterism. Still, this object made it into John Herschel's "General Catalog", later receiving the designation NGC 6994.
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