| Messier 13 | |
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The heart of Hercules Globular Cluster; Credit: ESA/Hubble and NASA |
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| Observation data (J2000 epoch) | |
| Class | V |
| Constellation | Hercules |
| Right ascension | 16h 41m 41.44s[1] |
| Declination | +36° 27′ 36.9″[1] |
| Distance | 25,100 light years |
| Apparent magnitude (V) | +5.8[1] |
| Apparent dimensions (V) | 20 arcmins |
| Physical characteristics | |
| Mass | 6×105 [2] M☉ (1036 kg) |
| Radius | 84 ly[3] |
| Estimated age | 1.4×1010 yr |
| Notable features | one of the best-known clusters of the northern hemisphere |
| Other designations | NGC 6205[1] |
| 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 or the Hercules Globular Cluster) is a globular cluster of about 300,000 stars in the constellation of Hercules.
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M13 was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764.
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. 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.
M13 is about 145 light-years in diameter, and it is composed of several hundred thousand stars, the brightest of which is the variable star V11 with an apparent magnitude of 11.95. M13 is 25,100 light-years away from Earth.
The Arecibo message of 1974, designed to communicate the existence of human life to hypothetical extraterrestrials, was transmitted toward M13. The reason was that with a higher star density, the chances of a life harboring planet with intelligent life forms, were believed to be higher. Even though the message was transmitted, M13 will no longer be in that location when it arrives. The sending of the message was more of a technological demonstration, rather than an actual attempt to contact life.
Coordinates: 16h 41m 41.44s, +36° 27′ 36.9″
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