Messier 72
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Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the very mildly southern constellation of Aquarius.
Observational history and guide
M72 was discovered by astronomer Pierre Méchain in 1780.Template:Efn His countryman Charles Messier looked for it 36 days later, and included it in his catalog.[1] Both opted for the then-dominant of the competing terms for such objects, considering it a faint nebula rather than a cluster. With a larger instrument, astronomer John Herschel called it a bright "cluster of stars of a round figure". Astronomer Harlow Shapley noted a similarity to Messier 4 and 12.[2]
It is visible in a good night sky as a faint nebula in a telescope with a Script error: No such module "convert". aperture. The surrounding field stars become visible from a Script error: No such module "convert".-aperture device. One of Script error: No such module "convert". will allow measurement of an angular diameter of 2.5 [[arcminutes|Template:Prime]]. At Script error: No such module "convert". the core is clear: its 1.25 [[arcminutes|Template:Prime]] diameter, meaning a broad spread; and small parts scarcer in stars to the south and east.[3]
Properties
Based upon a 2011 census of variable stars, the cluster is Script error: No such module "convert". away from the Sun.[4] It has an estimated combined mass of 168,000[5] solar masses (Template:Solar mass) and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times solar luminosity (Template:Lo) per cubic parsec.[6] There are 43 identified variable stars in the cluster.[4]
Image Gallery
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M72 imaged by the Hubble Space Telescope
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See also
References and footnotes
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External links
- Messier 72, SEDS Messier pages
- Messier 72, Galactic Globular Clusters Database page
- Messier 72, LRGB CCD image based on two hours total exposure
- M-72 Information
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