M72 was discovered by astronomerPierre Méchain in 1780.[a] His countrymanCharles Messier looked for it 36 days later, and included it in his catalog.[8] Both opted for the then-dominant of the competing terms for such objects, considering it a faintnebula rather than a cluster. With a larger instrument, astronomerJohn Herschel called it a bright "cluster of stars of a round figure". AstronomerHarlow Shapley noted a similarity toMessier 4 and12.[9]
It is visible ina good night sky as a faint nebula in a telescope with a 6 cm (2.4 in)aperture. The surrounding field stars become visible from a 15 cm (5.9 in)-aperture device. One of 25 cm (9.8 in) will allow measurement of anangular diameter of 2.5 ′. At 30 cm (12 in) the core is clear: its 1.25 ′ diameter, meaning a broad spread; and small parts scarcer in stars to the south and east.[10]
Based upon a 2011 census of variable stars, the cluster is 54.57 ± 1.17 kly (16.73 ± 0.36 kpc) away from theSun.[3] It has an estimated combined mass of 168,000[5]solar masses (M☉) and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times solar luminosity (L☉) per cubicparsec.[6] There are 43 identified variable stars in the cluster.[3]
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters",Harvard College Observatory Bulletin,849 (849):11–14,Bibcode:1927BHarO.849...11S.
^abcdFiguera Jaimes, R.; et al. (October 2011), Henney, W. J.; Torres-Peimbert, S. (eds.), "XIII Latin American Regional IAU Meeting: (item) The Globular Cluster NGC 6981: Variable stars population, physical parameters and astrometry",Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias, vol. 40, pp. 235–236,Bibcode:2011RMxAC..40..235F.
^"Messier 72".SEDS Messier Catalog. Archived fromthe original on 1 July 2022. Retrieved30 April 2022.
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