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The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. [4] [5] [6] The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, [7] then finally as a globular cluster in the early 19th century ...
This cluster is one of the largest and brightest, and is made up of around 500,000 stars. [11] It is estimated to be 11.4 billion years old. [ 8 ] It is centered at 32,600 light-years (10.0 kpc ) away from Earth .
It is at a distance of 28,000 light years away from Earth, and is currently part of the Galactic bulge. [3] NGC was discovered by the German-born British astronomer William Herschel on 24 May 1784. [6] It was initially thought to be an open cluster, but its true nature as a globular cluster was later confirmed. It is a core-collapse cluster. [3]
These new-found star clusters contain hundreds of thousands of stars, a similar number to globular clusters. The clusters also share other characteristics with globular clusters, e.g. the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across ...
Moving cluster parallax is a technique where the motions of individual stars in a nearby star cluster can be used to find the distance to the cluster. Only open clusters are near enough for this technique to be useful.
The brightest stars in M56 are of 13th magnitude, while it contains only about a dozen known variable stars, such as V6 (RV Tauri star; period: 90 days) or V1 (Cepheid: 1.510 days); [12] other variable stars are V2 (irregular) and V3 (semiregular). In 2000, a diffuse X-ray emission was tentatively identified coming from the vicinity of the cluster.
Home to over 100,000 stars, [11] the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15-C. It also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. [13] [14] Just three others have been found in globular clusters since ...
Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius.It was discovered by French astronomer Charles Messier in 1764. [11] [a] He briefly described it as a "nebula containing no star... round, seen with difficulty in 3 1 ⁄ 2-foot telescope; Diam 2′."