Messier 13 or M13 (also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules, the Hercules Globular Cluster, or the Great Hercules Cluster), is a
globular cluster of several hundred thousand
stars in the
constellation of
Hercules.
Discovery and visibility
Messier 13 was discovered by
Edmond Halley in 1714,[2] and cataloged by
Charles Messier on June 1, 1764,[9] into his list of objects not to mistake for
comets; Messier's list, including Messier 13, eventually became known as the
Messier catalog.[10] It is located at
right ascension 16h 41.7m,
declination +36° 28'. Messier 13 is often described by astronomers as the most magnificent globular cluster visible to northern observers.[2]
About one third of the way from Vega to Arcturus, four bright stars in
Hercules 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. With an
apparent magnitude of 5.8,[2] Messier 13 may be visible to the
naked eye with
averted vision on dark nights.[2] Messier 13 is prominent in traditional
binoculars as a bright, round patch of light.[2] Its diameter is about 23 arcminutes and it is readily viewable in small telescopes.[11] 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.[12] The cluster is visible throughout the year from latitudes greater than 36 degrees north, with the longest visibility during
Northern Hemisphere spring and summer.[13]
Nearby to Messier 13 is
NGC 6207, a 12th-magnitude edge-on galaxy that lies 28 arcminutes directly northeast.[14] 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.[15]
Characteristics
About 145
light-years in
diameter, M13 is composed of several hundred thousand
stars, with estimates varying from around 300,000 to over half a million.[15] The brightest star in the cluster is a
red giant, the
variable star V11, also known as V1554 Herculis,[16] with an apparent visual magnitude of 11.95. M13 is 22,200–25,000 light-years away from
Earth,[9] and the globular cluster is one of over one hundred that orbit the center of the Milky Way.[17][18]
Single stars in this globular cluster were first resolved in 1779.[9] Compared to the stars in the neighborhood of the
Sun, the stars of the M13 population are more than a hundred times more densely packed.[9] They are so close together that they sometimes collide and produce new stars.[9] The newly formed, young stars, known as "
blue stragglers", are particularly interesting to astronomers.[9]
The last three variables (V63, V64 and V65) were discovered from Spain in April 2021, March 2022 and January 2024 respectively.
The 1974
Arecibo message, which contained encoded information about the human race, DNA, atomic numbers, Earth's position and other information, was beamed from the
Arecibo Observatory radio telescope towards Messier 13 as an experiment in contacting potential extraterrestrial civilizations in the cluster. M13 was chosen because it was a large, relatively close star cluster that was available at the time and place of the ceremony.[19] The cluster will move through space during the transit time; opinions differ as to whether or not the cluster will be in a position to receive the message by the time that it arrives.[20][21]
In the German science fiction series Perry Rhodan, M13 is the location of Arkon, the homeworld of the race of Arkonides.
In author
Dan Simmons' Hyperion Cantos the Hercules cluster is where a copy of Earth was secretly recreated after the original was destroyed.
In his novel The Sirens of Titan,
Kurt Vonnegut writes "Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules—and still there are some misfits who insist that there is no such thing as progress."
Messier 13 is the home of the antagonistic aliens in the 1977
space operaThe War in Space, who hail from the third planet of a system orbiting a star called Yomi.
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14,
Bibcode:
1927BHarO.849...11S.