Messier 7 or M7, also designated NGC 6475 and sometimes known as the Ptolemy Cluster, is an open cluster of

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 origins of the e ...

of Scorpius. The cluster is easily detectable with the naked eye, close to the "stinger" of Scorpius. With a

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. Declination's angle is measured north or south of the ...

of −34.8°, it is the southernmost Messier object. M7 has been known since

antiquity Antiquity or Antiquities may refer to: Historical objects or periods Artifacts *Antiquities, objects or artifacts surviving from ancient cultures Eras Any period before the European Middle Ages (5th to 15th centuries) but still within the histo ...

; it was first recorded by the 2nd-century Greek-Roman astronomer Ptolemy, who described it as a

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

in 130 AD. Italian astronomer

Giovanni Batista Hodierna Giovanni Battista Hodierna, also spelled as Odierna (April 13, 1597 – April 6, 1660) was an Italian astronomer at the court of Giulio Tomasi, Duke of Palma (Palma di Montechiaro). He compiled a catalogue of comets and other celestial object ...

observed it before 1654 and counted 30

s in it. In 1764, French astronomer Charles Messier catalogued the cluster as the seventh member in his list of comet-like objects. English astronomer

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...

described it as "coarsely scattered clusters of stars".

Telescopic A telescope is an instrument designed for the observation of remote objects. Telescope(s) also may refer to: Music * The Telescopes, a British psychedelic band * ''Telescope'' (album), by Circle, 2007 * ''The Telescope'' (album), by Her Space H ...

observations of the cluster reveal about 80 stars within a field of view of 1.3° across. At the cluster's estimated distance of 980

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s this corresponds to an actual diameter of 25 light years. The

tidal radius A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

of the cluster is and it has a combined mass of about 735 times the mass of the Sun. The age of the cluster is around 200 million years while the brightest member star is of magnitude 5.6. In terms of composition, the cluster contains a similar abundance of elements other than hydrogen and helium as the Sun. On August 29, 2006, Messier 7 was used for first light image of the Long Range Reconnaissance Imager (LORRI) telescope on the Pluto-bound

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...

spacecraft. As of January 2022, Messier 7 is one of the few remaining Messier objects not photographed by the Hubble Space Telescope. This is mainly due to those objects' angular diameter or lack of scientific significance. Most such objects are open clusters of large angular diameter that would require thousands of photos due to Hubble's small field of view. (For comparison, Hubble's well known panoramic photo of the Andromeda Galaxy, covering less than half of our galactic neighbor, required approximately 400 individual movements and 7400 exposures.)

Gallery

Messier 7.jpg, Broader view of M7, with the cluster at the center of the image

References

External links

Messier 7, SEDS Messier pages
* *
New Horizons probe captures M7
* {{DEFAULTSORT:Messier 007 Astronomical objects known since antiquity

007 The ''James Bond'' series focuses on a fictional British Secret Service agent created in 1953 by writer Ian Fleming, who featured him in twelve novels and two short-story collections. Since Fleming's death in 1964, eight other authors have ...

NGC objects Open clusters Orion–Cygnus Arm Scorpius (constellation)

Gallery

See also

References

External links