M13 was discovered by
Edmond Halley in 1714, and cataloged by
Charles Messier on June 1, 1764, into his list of objects.About one third of the way from Vega to Arcturus, four bright stars in
Herculēs form the Keystone
asterism, the broad torso of the hero. M13 can be seen in this asterism 2⁄3 of the way north (
by west) from
Zeta to
Eta Herculis. Although only telescopes with great light-gathering capability fully resolve the stars of the cluster, M13 may be visible to the
naked eye depending on circumstances. With a low-power telescope, Messier 13 looks like a comet or fuzzy patch. The cluster is visible throughout the year from latitudes greater than 36 degrees north, with the longest visibility during
Northern Hemisphere spring and summer.
About 145
light-years in
diameter, M13 is composed of several hundred thousand
stars, the brightest of which is a
red giant, the
variable star V11, also known as V1554 Herculis, with an apparent visual magnitude of 11.95. M13 is 22,200–25,000 light-years away from
Earth.
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