Messier 13

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Messier 13
Heart of M13 Hercules Globular Cluster.jpg
The heart of Hercules Globular Cluster
Credit: ESA/Hubble and NASA
Observation data (J2000 epoch)
Class V[1]
Constellation Hercules
Right ascension 16h 41m 41.24s[2]
Declination +36° 27′ 35.5″[2]
Distance 22.2 kly (6.8 kpc)[3]
Apparent magnitude (V) +5.8[4]
Apparent dimensions (V) 20 arcmins
Physical characteristics
Mass 6×105[5] M
Radius 84 ly[6]
Metallicity  = –1.33[7] dex
Estimated age 11.65 Gyr[7]
Notable features one of the best-known clusters of the northern hemisphere
Other designations NGC 6205[4]
See also: Globular cluster, List of globular clusters
M13 from an 8" SCT in San Diego, CA

Messier 13 (M13), also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules or the Hercules Globular Cluster, is a globular cluster of about 300,000 stars in the constellation of Hercules.

Discovery and visibility[edit]

M13 was discovered by Edmond Halley in 1714, and cataloged by Charles Messier on June 1, 1764. Charles had a list of more than a 100 objects that later became known as the Messier Catalog. The French astronomer mistook these objects for comets, but compiled them into a list to help future scientists.[8]

Less than halfway from Arcturus to Vega, four bright stars in the constellation of Hercules form the Keystone. M13 can be seen in the middle of Zeta Herculis and Eta Herculis. Only telescopes with a great light-gathering capability can best show the Hercules Globular Cluster. M13 is not clearly visible to the naked eye. With a low-power telescope, the Messier 13 looks like a comet. The cluster can be seen all year long at latitudes greater than 36 degrees north, on some nights more than others. However, in the months of August and September it brightens the sky for a longer period of time.[9]

It is located at right ascension 16h 41.7m and declination +36° 28'. With an apparent magnitude of 5.8, it is barely visible with the naked eye on a very clear night. Its diameter is about 23 arc minutes and it is readily viewable in small telescopes.[10] Nearby is NGC 6207, a 12th magnitude edge-on galaxy that lies 28 arc minutes directly north east. A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center.

Traditional binoculars make the Hercules Globular Cluster look similar to a round patch of light. A four to six inch telescope is recommended to observe M13 as the stars will be seen as small pinpoints of light. Larger telescopes provide a closer look and improve the view.[11]

Wide field image of Messier 13.


M13 is about 145 light-years in diameter, and it is composed of several hundred thousand stars, the brightest of which is a red giant, the variable star V11, with an apparent visual magnitude of 11.95. M13 is 22,200 light-years away from Earth.

It wasn't until 1779 that the single stars in this globular cluster were resolved. Compared to the stars surrounding the vicinity of the sun, M13 stellar population is more than a hundred times greater. These stars are so densely packed together that they often collide and produce new stars. The newly-formed, young stars, so-called "blue stragglers," are particularly interesting to astronomers.[12]

The Arecibo message of 1974, 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 M13 as an experiment in contacting potential extraterrestrial civilizations in the cluster. While the cluster will move through space during the transit time, the proper motion is small enough that the cluster will only move 24 light years, only a fraction of the diameter of the cluster. Thus, the message will still arrive near the center of the cluster.[13]

Literary references[edit]

  • The science fiction novellas "Sucker Bait" by Isaac Asimov and "Question and Answer" by Poul Anderson take place on Troas, a world within M13.
  • In the science fiction series Perry Rhodan, M13 is the location of Arkon, the home world of the race of Arkonides.
  • In author Dan Simmon's Hyperion Cantos the Hercules cluster is where a copy of Earth was secretly recreated after the original was destroyed.
  • In the fantasy fiction series The Sphere's Legend, M13 is the location of Zim, the home world of the Zimians.
  • In 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."
  • Deliberately engineering a star in Messier 13 to go nova was part of the Cybermen’s complicated plot in the 1968 Doctor Who story The Wheel in Space.
  • In Bill Amend's popular comic strip FoxTrot, Jason Fox mentions observing the M13 Globular Cluster.
M13 is in "armpit" of Hercules constellation

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 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:1008.2755Freely accessible, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830. 
  3. ^ 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. 
  4. ^ a b "M 13". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15. 
  5. ^ 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. 
  6. ^ distance × sin( diameter_angle / 2 ) = 84 ly radius
  7. ^ 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:1001.4289Freely accessible, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x. 
  8. ^ "Messier 13 (M13) - The Great Hercules Cluster - Universe Today". Universe Today. 2016-05-09. Retrieved 2018-04-23. 
  9. ^ "M13: Great Cluster in Hercules |". Retrieved 2018-03-26. 
  10. ^ "M 13". Messier Objects Mobile -- Charts, Maps & Photos. 2016-10-16. Retrieved 2018-04-23. 
  11. ^ "How to See the Great Hercules Cluster of Stars". Retrieved 2018-04-23. 
  12. ^ Garner, Rob (2017-10-06). "Messier 13 (The Hercules Cluster)". NASA. Retrieved 2018-04-23. 
  13. ^ "Science 2.0". In regard to the email from. Retrieved 2015-04-15. 

External links[edit]

Coordinates: Sky map 16h 41m 41.44s, 36° 27′ 36.9″