# Messier 13

M13 from an 8" SCT in San Diego, CA
Messier 13
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
Metallicity ${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –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]

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

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.[8] 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.

Wide field image of Messier 13.

## Characteristics

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 25,100 light-years away from Earth.[citation needed]

## Arecibo message

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.[9]

## 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 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