Messier 13

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**Messier 13**
Observation data (Epoch J2000)
Globular cluster	List of globular clusters

Class	V
Constellation	Hercules
Right ascension	16^h 41^m 41.44^s^[1]
Declination	+36° 27′ 36.9″^[1]
Distance	25.1 kly ()
Apparent magnitude (V)	+5.8^[1]
Apparent dimensions (V)	23′
Physical characteristics
Mass	( M_☉)
Radius	84 ly^[2]
V_HB
Estimated age	1.4×10¹⁰ yr
Notable features	one of the best well-known clusters of the northern hemisphere
Other designations	NGC 6205^[1]

The Great Globular Cluster in Hercules (also known as the Hercules Globular Cluster, Messier Object 13, Messier 13, M13, or NGC 6205) is a globular cluster in the Hercules constellation at right ascension 16^h 41.7^m and declination +36° 28'.

It was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764.

With an apparent magnitude of 5.8, it is barely visible with the naked eye on a very clear night. Its real diameter is about 145 light-years, and 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.

Its diameter is about 23 arc minutes and is readily viewable in small telescopes. Nearby is NGC 6207, a 12th magnitude edge on galaxy that lies 28 arc minutes directly north east. The J2000 coordinates are RA: 16h 41m 41.5s and Dec: +36° 27' 37".

The Arecibo message of 1974 was transmitted toward this globular cluster.

1 Literary references
2 See also
3 External links
4 References

[edit] Literary references

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 Earth was secretly moved to after it was supposedly destroyed.