Messier 72 (also known as M72 or NGC 6981) is a

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of memb ...

in the south west of the very mildly southern constellation of

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainment ...

Observational history and guide

M72 was discovered by astronomer

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was bo ...

in 1780. His countryman

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects''. Messier's purpose f ...

looked for it 36 days later, and included it in his catalog. Both opted for the then-dominant of the competing terms for such objects, considering it a faint

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

rather than a cluster. With a larger instrument, astronomer

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanic ...

called it a bright "cluster of stars of a round figure". Astronomer

Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to e ...

noted a similarity to

Messier 4 Messier 4 or M4 (also designated NGC 6121) is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first globular cluster in which ind ...

and 12. It is visible in a good night sky as a faint nebula in a telescope with a

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

. The surrounding field stars become visible from a -aperture device. One of will allow measurement of an

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it i ...

of 2.5 . At the core is clear: its 1.25 diameter, meaning a broad spread; and small parts scarcer in stars to the south and east.

Properties

Based upon a 2011 census of variable stars, the cluster is away from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

. It has an estimated combined mass of 168,000

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass o ...

es () and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times solar luminosity () per cubic

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, a ...

. There are 43 identified variable stars in the cluster. M72map

References and footnotes

External links

Messier 72, SEDS Messier pages

Messier 72, Galactic Globular Clusters Database page

* {{DEFAULTSORT:Messier 72 Messier 072 Messier 072 072 Messier 072 Astronomical objects discovered in 1780

Observational history and guide

Properties

See also

References and footnotes

External links