Messier 12 or M 12 (also designated NGC 6218) is a

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

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Ophiuchus Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constellati ...

. It was discovered by the French astronomer

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 ...

on May 30, 1764, who described it as a "nebula without stars". In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an

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 ...

of or greater. In a scope, the granular core shows a diameter of 3 (

arcminute A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s) surrounded by a 10 halo of stars. M12 is roughly 3° northwest from the cluster M10 and 5.6° east southeast from star

Lambda Ophiuchi λ Ophiuchi, Latinized as Lambda Ophiuchi, is a quadruple star system in the equatorial constellation of Ophiuchus. It has the traditional name Marfik , which now applies exclusively to the primary component. The system is visible to ...

. It is also located near the 6th magnitude 12 Ophiuchi. The cluster is about from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

and has a spatial diameter of about 75 light-years. The brightest stars of M12 are of 12th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

. M10 and M12 are only a few thousand light-years away from each other and each cluster would appear at about magnitude 4.5 from the other. With a Shapley-Sawyer rating of IX, it is rather loosely packed for a globular and was once thought to be a tightly concentrated

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

. Thirteen

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

s have been recorded in this cluster. M12 is approaching us at a velocity of 16 km/s. A study published in 2006 concluded that this cluster has an unusually low number of low-mass stars. The authors surmise that they were stripped from the cluster by passage through the relatively matter-rich plane of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. Image:M12 Hubble.jpg, Messier 12 core by HST Image:ESO-Messier 12-Phot-04a-06.jpg, The Central Part of Messier 12. Credit:

ESO The European Southern Observatory is an astronomical research organisation. ESO may also refer to: *Employee stock option (also: executive stock option) *'' Ether Saga Odyssey'', a fantasy massively multiplayer online role-playing game *''The Elde ...

Image:M12map.png, Map showing the location of M12

Notes

References

External links

Messier 12, SEDS Messier pagesMessier 12, Galactic Globular Clusters Database pageMessier 12, Amateur astrophotographer (hgg) with a Celestron 9.25"
* {{DEFAULTSORT:Messier 012 Globular clusters Ophiuchus

012 012 may refer to: * Tyrrell 012, a Formula One racing car * The dialing code for Pretoria Pretoria ( ; ) is the Capital of South Africa, administrative capital of South Africa, serving as the seat of the Executive (government), executive br ...

NGC objects 17640530 Discoveries by Charles Messier

See also

Notes

References

External links