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Messier 72 (also known as M72 or NGC 6981) is a
File:A glittering cluster shines again (potw2516a).jpg, M72 imaged by the
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 Discoveries by Pierre Méchain
globular cluster
A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
in the south west of the very mildly southern constellation of Aquarius.
Observational history and guide
M72 was discovered by astronomerPierre 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'', referred to with th ...
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 (; 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 regions, such as in the Pillars of Creation in ...
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 and experimental photographer who invented the blueprint and did botanical work. ...
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 astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal.
Shapley used Cepheid var ...
noted a similarity to Messier 4
Messier 4 or M4 (also known as NGC 6121 or the Spider Globular Cluster) 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 g ...
and 12.
It is visible in a good night sky as a faint nebula in a telescope with a aperture
In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
. 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 separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...
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 theSun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. It has an estimated combined mass of 168,000 solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
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, and ...
. There are 43 identified variable stars in the cluster.
Image Gallery
Hubble Space Telescope
The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
See also
*List of Messier objects
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of th ...
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 Discoveries by Pierre Méchain