Messier 28 or M28, also known as NGC 6626, 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 ...
of stars in the center-west of
Sagittarius. It was discovered by 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 ...
in 1764.
[ He briefly described it as a "nebula containing no star... round, seen with difficulty in 3-foot telescope; Diam 2]′
The prime symbol , double prime symbol , triple prime symbol , and quadruple prime symbol are used to designate units and for other purposes in mathematics, science, linguistics and music.
Although the characters differ little in appearance fr ...
."[
In the sky it is less than a degree to the northwest of the 3rd ]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 ...
star Kaus Borealis
Lambda Sagittarii (Romanization of Greek, Latinized from λ Sagittarii), formally named Kaus Borealis , is a star in the southern constellation of Sagittarius (constellation), Sagittarius. The star marks the top of the Archer's bow.
...
(Lambda ). This cluster is faintly visible as a hazy patch with a pair of binoculars[ and can be readily found in a small 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 ...
, showing as a nebulous feature spanning 11.2 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. Using an aperture of , the core becomes visible and a few distinct stars can be resolved, along the periphery. Larger telescopes will provide greater resolution,[ one of revealing a dense 2′ core, with more density within.][
It is about 18,300 ]light-year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s away 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 ...
.[ It is about ][ and its metallicity (averaging −1.32 which means more than 10 times less than our own star), coherency and preponderence of older ]stellar evolution
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...
objects, support its dating to very roughly 12 billion years old.[ 18 RR Lyrae type ]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 found within.
It bore the first discovery of a millisecond pulsar
A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...
in a globular cluster – PSR B1821–24. This was using the Lovell Telescope
The Lovell Telescope ( ) is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire, in the north-west of England. When construction was finished in 1957, the telescope was the largest steerable dish radio telescope in the world a ...
at Jodrell Bank Observatory
Jodrell Bank Observatory ( ) in Cheshire, England hosts a number of radio telescopes as part of the Jodrell Bank Centre for Astrophysics at the University of Manchester. The observatory was established in 1945 by Bernard Lovell, a radio as ...
, England.Green Bank Observatory
The Green Bank Observatory (previously National Radio Astronomy Observatory, Green Bank) is an Observatory, astronomical observatory located in the United States National Radio Quiet Zone, National Radio Quiet Zone in Green Bank, West Virginia, G ...
, West Virginia
West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...
. As of 2011, these number the third-most in a cluster tied to the Milky Way, following Terzan 5 and 47 Tucanae
47 Tucanae or 47 Tuc (also designated as NGC 104 and Caldwell 106) is a globular cluster located in the constellation Tucana. It is about from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magni ...
.[
]
Gallery
File:Nebulous, but no nebula Messier 28.jpg, Messier 28 taken by Hubble.2MASS
The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...
; wide angle
File:M28map.png, Map showing location of M28
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
References
Footnotes
External links
Globular Cluster M28 @ SEDS Messier pages
Messier 28, Galactic Globular Clusters Database page
*
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Discoveries by Charles Messier