Messier 13, or M13 (also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules, the Hercules Globular Cluster, or the Great Hercules Cluster), is a

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

of several hundred thousand

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

Discovery and visibility

Messier 13 was discovered by

Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Hal ...

in 1714, and cataloged by

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...

on June 1, 1764, into his list of objects not to mistake for

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

s; Messier's list, including Messier 13, eventually became known as the

Messier catalog The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of thos ...

. It is located at

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

16^h 41.7^m,

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

+36° 28'. Messier 13 is often described by astronomers as the most magnificent globular cluster visible to northern observers. About one third of the way from Vega to Arcturus, four bright stars in

form the Keystone asterism, the broad torso of the hero. M13 can be seen in this asterism of the way north ( by west) from

Zeta Zeta (, ; uppercase Ζ, lowercase ζ; , , classical or ''zē̂ta''; ''zíta'') is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived from the Phoenician alphabet, Phoenician letter zay ...

to Eta Herculis. With an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 5.8, Messier 13 may be visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

with averted vision on dark nights. Messier 13 is prominent in traditional

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

as a bright, round patch of light. Its diameter is about 23 arcminutes and it is readily viewable in small telescopes. At least four inches of telescope aperture resolves stars in Messier 13's outer extent as small pinpoints of light. However, only larger telescopes resolve stars further into the center of the cluster. The cluster is visible throughout the year from latitudes greater than 36 degrees north, with the longest visibility during

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

spring and summer. Nearby to Messier 13 is NGC 6207, a 12th-magnitude edge-on galaxy that lies 28 arcminutes directly northeast. A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center. At low powers the cluster is bracketed by two seventh-magnitude stars.

Characteristics

About 145

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

, M13 is composed of several hundred thousand

s, with estimates varying from around 300,000 to over half a million. The brightest star in the cluster is a

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

, the

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

V11, also known as V1554 Herculis, with an apparent visual magnitude of 11.95. M13 is 22,200 to 25,000 light-years away from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, and the globular cluster is one of over one hundred that orbit the center of the Milky Way. The stars in this cluster are firmly in the Population II category, markedly lower in

metals A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against no ...

than Population I stars like the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

and most other stars in the Sun's close proximity. M13 as a whole has only about 4.6% as much

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

as the Sun does. Single stars in this globular cluster were first resolved in 1779. Compared to the stars in the neighborhood of the

, the stars of the M13 population are more than a hundred times more densely packed. They are so close together that they sometimes collide and produce new stars. The newly formed, young stars, known as "

blue straggler A blue straggler is a type of star that is more luminous and bluer than expected. Typically identified in a stellar cluster, they have a higher effective temperature than the main sequence turnoff point for the cluster, where ordinary stars b ...

s", are particularly interesting to astronomers. The last three variables (V63, V64 and V65) were discovered from Spain in April 2021, March 2022 and January 2024, respectively.

Arecibo message

The 1974

Arecibo message The Arecibo message is an interstellar radio message carrying basic information about humanity and Earth that was sent to the globular cluster Messier 13 in 1974. It was meant as a demonstration of human technological achievement, rather than ...

, which contained encoded information about the human race, DNA, atomic numbers, Earth's position and other information, was beamed from the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

radio telescope towards Messier 13 as an experiment in contacting potential extraterrestrial civilizations in the cluster. M13 was chosen because it was a large, relatively close star cluster that was available at the time and place of the ceremony. The cluster will move through space during the transit time; opinions differ as to whether or not the cluster will be in a position to receive the message by the time that it arrives.

Literary references

* The

science fiction Science fiction (often shortened to sci-fi or abbreviated SF) is a genre of speculative fiction that deals with imaginative and futuristic concepts. These concepts may include information technology and robotics, biological manipulations, space ...

novellas " Sucker Bait" by

Isaac Asimov Isaac Asimov ( ; – April 6, 1992) was an Russian-born American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. H ...

and the novel ''Question and Answer'' by

Poul Anderson Poul William Anderson ( ; November 25, 1926 – July 31, 2001) was an American fantasy and science fiction author who was active from the 1940s until his death in 2001. Anderson also wrote historical novels. He won the Hugo Award seven times an ...

take place on Troas, a world within M13. * In the German science fiction series '' Perry Rhodan'', M13 is the location of Arkon, the homeworld of the race of Arkonides. * In author

Dan Simmons Dan Simmons (born April 4, 1948) is an American science fiction and horror writer. He is the author of the Hyperion Cantos and the Ilium/Olympos cycles, among other works that span the science fiction, horror, and fantasy genres, sometimes ...

' '' Hyperion Cantos'' the Hercules cluster is where a copy of Earth was secretly recreated after the original was destroyed. * In his novel ''

The Sirens of Titan ''The Sirens of Titan'' is a comic science fiction novel by Kurt Vonnegut Jr., first published in 1959. His second novel, it involves issues of free will, omniscience, and the overall purpose of human history, with much of the story revolving ...

'',

Kurt Vonnegut Kurt Vonnegut ( ; November 11, 1922 – April 11, 2007) was an American author known for his Satire, satirical and darkly humorous novels. His published work includes fourteen novels, three short-story collections, five plays, and five nonfict ...

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." * Messier 13 is the home of the antagonistic aliens in the 1977

space opera Space opera is a subgenre of science fiction that emphasizes Space warfare in science fiction, space warfare, with use of melodramatic, risk-taking space adventures, relationships, and chivalric romance. Set mainly or entirely in outer space, i ...

'' The War in Space'', who hail from the third planet of a system orbiting a star called Yomi. * Deliberately engineering a star in Messier 13 to go

nova A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...

was part of the Cybermen's complicated plot in the 1968 ''

Doctor Who ''Doctor Who'' is a British science fiction television series broadcast by the BBC since 1963. The series, created by Sydney Newman, C. E. Webber and Donald Wilson (writer and producer), Donald Wilson, depicts the adventures of an extraterre ...

'' story '' The Wheel in Space''.

Gallery

File:Hercules constellation map.png, M13 is in the "armpit" of the constellation Hercules. File:Heart of M13 Hercules Globular Cluster.jpg, Heart of the Hercules Globular Cluster, Hubble image File:Hubble’s Views of M13 (2010) and M3 (2019).jpg, Hubble images comparing M13 and M3

References

External links

Messier 13, SEDS Messier pages

L199 (V63), a new variable star in M13

Variability of L261 in M13 (V64)

Study of the variable stars V10 and C6 in M13 (V65)

Messier 13, Galactic Globular Clusters Database page

* ttp://www.astrovox.gr/forum/album_pic.php?pic_id=16664 Messier 13, Amateur astrophotographer (hgg) photo using the 9.25" Celestron Telescope (85-min. exposure)
M13 Hercules Globular photo detail Dark Atmospheres

* ttps://ui.adsabs.harvard.edu/abs/2019AcA....69..101O/abstract Variable Stars in M13. III. The Cepheid Variables and their Relation to Evolutionary Changes in Metal-Poor BL Her Stars.
Messier 13, Image by Waid Observatory

NightSkyInfo.com – M13, the Hercules Globular Cluster

Photometric study of the V2 cepheid in M13

Period, Amplitude and Light Curve of V38 in M13

* {{DEFAULTSORT:Messier 13 Messier 013 Messier 013 013 Milky Way Messier 013 ?