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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 in the constellation of Hercules.
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.
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