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'''Messier 13''' or '''M13''', also designated '''NGC 6205''' and sometimes called the '''Great Globular Cluster in Hercules''' or the '''Hercules Globular Cluster''', is a [[globular cluster]] of several hundred thousand [[star]]s in the [[constellation]] of [[Hercules (constellation)|Hercules]] of the [[Milky Way]] galaxy.
==Discovery and visibility==
Messier 13 was discovered by [[Edmond Halley]] in 1714,<ref name=Thompson2007 /> and cataloged by [[Charles Messier]] on June 1, 1764,<ref name="garner" /> into his list of objects not to mistake for [[comet]]s; Messier's list, including Messier 13, eventually became known as the [[Messier object|Messier catalog]].<ref>{{Cite news|url=https://www.universetoday.com/31430/messier-13/|title=Messier 13 (M13) - The Great Hercules Cluster - Universe Today|date=2016-05-09|work=Universe Today|access-date=2018-04-23|language=en-US}}</ref> It is located at [[right ascension]] 16<sup>h</sup> 41.7<sup>m</sup>, [[declination]] +36° 28'. Messier 13 is often described by astronomers as the most magnificent globular cluster visible to northern observers.<ref name=Thompson2007 />
About one third of the way from [[Vega]] to [[Arcturus]], four bright stars in [[Hercules (constellation)|Hercules]] form the Keystone [[Asterism (astronomy)|asterism]], the broad torso of the hero. M13 can be seen in this asterism {{frac|2|3}} of the way north ([[boxing the compass|by west]]) from [[Zeta Herculis|Zeta]] to [[Eta Herculis]]. With an [[apparent magnitude]] of 5.8,<ref name=Thompson2007 /> Messier 13 may be visible to the [[naked eye]] with [[averted vision]] on dark nights.<ref name=Thompson2007 /> Messier 13 is prominent in traditional [[binoculars]] as a bright, round patch of light.<ref name=Thompson2007 /> Its diameter is about 23 arcminutes and it is readily viewable in small telescopes.<ref>{{Cite news|url=https://messierobjects101.com/messier-object-m-13/|title=M 13|date=2016-10-16|work=Messier Objects Mobile -- Charts, Maps & Photos|access-date=2018-04-23|language=en-US}}</ref> At least four inches of telescope aperture resolves stars in Messier 13's outer extent as small pinpoints of light. However, only larger telescopes resolve stars further into the center of the cluster.<ref>{{Cite news|url=https://www.space.com/12021-hercules-star-cluster-night-sky-m13-messier.html|title=How to See the Great Hercules Cluster of Stars|work=Space.com|access-date=2018-04-23}}</ref> The cluster is visible throughout the year from latitudes greater than 36 degrees north, with the longest visibility during [[Northern Hemisphere]] spring and summer.<ref>{{Cite web|url=http://earthsky.org/clusters-nebulae-galaxies/m13-finest-globular-cluster-in-northern-skies#how|title=M13: Great Cluster in Hercules {{!}} EarthSky.org|website=earthsky.org|language=en-US|access-date=2018-03-26}}</ref>
Nearby to Messier 13 is [[NGC 6207]], a 12th-magnitude edge-on galaxy that lies 28 arcminutes directly northeast.<ref>{{cite web|title=NGC 6207|url=http://observing.skyhound.com/archives/jun/NGC_6207.html|website=Skyhound|access-date=26 March 2023}}</ref> A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center. At low powers the cluster is bracketed by two seventh–magnitude stars.<ref name=OMeara1998 />
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