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Messier 13

Coordinates: Sky map 16h 41m 41.44s, 36° 27′ 36.9″
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Messier 13
Globular cluster Messier 13 in Hercules
Observation data (J2000 epoch)
Right ascension16h 41m 41.24s[3]
Declination+36° 27′ 35.5″[3]
Distance22.2 kly (6.8 kpc)[4]
Apparent magnitude (V)5.8[5]
Apparent dimensions (V)20 arcminutes
Physical characteristics
Absolute magnitude–8.5
Mass6×105[6] M
Radius84 ly[7]
Metallicity = –1.33[8] dex
Estimated age11.65 Gyr[8]
Notable featuresOne of the best-known clusters of the Northern Hemisphere
Other designationsNGC 6205[5]
See also: Globular cluster, List of globular clusters

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[edit]

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 23 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]


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]

The stars in this cluster are firmly in the Population II category, markedly lower in metals than Population I stars like the Sun and most other stars in the Sun's close proximity. M13 as a whole has only about 4.6% as much iron as the Sun does.

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.

Arecibo message[edit]

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]

Literary references[edit]


See also[edit]


  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
  2. ^ a b c d e f Thompson, Robert; Thompson, Barbara (2007). Illustrated Guide to Astronomical Wonders: From Novice to Master Observer. DIY science. O'Reilly Media, Inc. p. 258. ISBN 978-0596526856.
  3. ^ a b Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830, S2CID 119183070.
  4. ^ Paust, Nathaniel E. Q.; et al. (February 2010), "The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions", The Astronomical Journal, 139 (2): 476–491, Bibcode:2010AJ....139..476P, doi:10.1088/0004-6256/139/2/476, hdl:2152/34371, S2CID 120965440.
  5. ^ a b "M 13". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.
  6. ^ Leonard, Peter J. T.; Richer, Harvey B.; Fahlman, Gregory G. (1992), "The mass and stellar content of the globular cluster M13", Astronomical Journal, 104: 2104, Bibcode:1992AJ....104.2104L, doi:10.1086/116386.
  7. ^ distance × sin(diameter_angle / 2) = 84 ly radius
  8. ^ a b Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x, S2CID 51825384.
  9. ^ a b c d e f Garner, Rob (2017-10-06). "Messier 13 (The Hercules Cluster)". NASA. Retrieved 2018-04-23.
  10. ^ "Messier 13 (M13) - The Great Hercules Cluster - Universe Today". Universe Today. 2016-05-09. Retrieved 2018-04-23.
  11. ^ "M 13". Messier Objects Mobile -- Charts, Maps & Photos. 2016-10-16. Retrieved 2018-04-23.
  12. ^ "How to See the Great Hercules Cluster of Stars". Space.com. Retrieved 2018-04-23.
  13. ^ "M13: Great Cluster in Hercules | EarthSky.org". earthsky.org. Retrieved 2018-03-26.
  14. ^ "NGC 6207". Skyhound. Retrieved 26 March 2023.
  15. ^ a b O'Meara, Stephen James; Levy, David H. (1998), Deep-Sky Companions: The Messier Objects, Cambridge University Press, p. 69, ISBN 978-0521553322.
  16. ^ Samus, N.N.; Pastukhova, E.N.; Durlevich, O.V.; Kazarovets, E.V.; Kireeva, N.N. (2020), "The 83rd Name-List of Variable Stars. Variables in Globular Clusters and Novae", Peremennye Zvezdy (Variable Stars) 40, No. 8, 40 (8): 8, Bibcode:2020PZ.....40....8S, doi:10.24411/2221-0474-2020-10009
  17. ^ "Control Telescope :: Stars & Nebulae". Retrieved 2021-11-22.
  18. ^ "Star Cluster". Retrieved 2021-11-22.
  19. ^ Larry Klaes (2005-11-30). "Making Contact". Ithaca Times. Archived from the original on 2009-01-07. Retrieved 2007-07-27.
  20. ^ "It's the 25th anniversary of Earth's first attempt to phone E.T." 1999-11-12. Archived from the original on 2008-08-02. Retrieved 2018-06-28.
  21. ^ "Science 2.0". In regard to the email from. Archived from the original on 2015-09-24. Retrieved 2015-04-15.

External links[edit]