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A '''globular cluster''' is a spherical grouping of [[star|stars]] that share a common origin and orbits the galactic core of a [[galaxy]] as a satellite.  They are very tightly bound by [[gravity]] and contain anywhere from tens of thousands to million of stars in an area that is only some 300 light years across or less, and are generally oblate spheroids in shape.  The density of the clusters are on average around 0.4 stars per cubic [[parsec]], but increases toward to the center of the cluster, reaching as high as 100 or even a 1000 stars per cubic parsec.<ref>http://www.astro.keele.ac.uk/workx/globulars/globulars.html</ref>

A '''globular cluster''' is a spherical grouping of [[star]]s that share a common origin and orbits the galactic core of a [[galaxy]] as a satellite.  They are very tightly bound by [[gravity]] and contain anywhere from tens of thousands to million of stars in an area that is only some 300 light years across or less, and are generally oblate spheroids in shape.  The density of the clusters are on average around 0.4 stars per cubic [[parsec]], but increases toward to the center of the cluster, reaching as high as 100 or even a 1000 stars per cubic parsec.<ref>http://www.astro.keele.ac.uk/workx/globulars/globulars.html</ref>

Unlike [[open cluster|open clusters]], which contain [[metallicity|population I stars]] and reside in the [[galactic disk]], globular clusters are made up of population II stars and are found in either the [[galactic bulge]] or [[galactic halo]].  Some globular clusters are found as far out as 131,000 light years from the core of the galaxy.<ref>http://adsabs.harvard.edu/abs/1996A&A...313..119D</ref>  Current, there are 158 known globular clusters around the [[Milky Way]], with several more perhaps yet to be discovered, all moving in highly eccentric orbits.<ref>http://www.seds.org/~spider/spider/MWGC/mwgc.html</ref>  Beyond the Milky Way, most other galaxies in the Local Group and beyond have globular clusters.  [[Andromeda_galaxy|Andromeda]] is known to have some 500.

Unlike [[open cluster]]s, which contain [[metallicity|population I stars]] and reside in the [[galactic disk]], globular clusters are made up of population II stars and are found in either the [[galactic bulge]] or [[galactic halo]].  Some globular clusters are found as far out as 131,000 light years from the core of the galaxy.<ref>http://adsabs.harvard.edu/abs/1996A&A...313..119D</ref>  Current, there are 158 known globular clusters around the [[Milky Way]], with several more perhaps yet to be discovered, all moving in highly eccentric orbits.<ref>http://www.seds.org/~spider/spider/MWGC/mwgc.html</ref>  Beyond the Milky Way, most other galaxies in the Local Group and beyond have globular clusters.  [[Andromeda galaxy|Andromeda]] is known to have some 500.

==History==

==History==