Messier 93 or M93, also known as NGC 2447 or the Critter Cluster, is an

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

in the modestly southern

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 ...

Puppis Puppis ("poop deck, stern") is a constellation in the southern sky. It was originally part of the Former constellations, traditional constellation of Argo Navis (the ship of Jason and the Argonauts), which was divided into three parts, the other ...

, the imagined poop deck of the legendary ''

Argo In Greek mythology, the ''Argo'' ( ; ) was the ship of Jason and the Argonauts. The ship was built with divine aid, and some ancient sources describe her as the first ship to sail the seas. The ''Argo'' carried the Argonauts on their quest fo ...

''.

Observational history and appearance

It was discovered 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 ...

then added to his catalogue of

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 ...

-like objects in 1781.

Caroline Herschel Caroline Lucretia Herschel ( , ; 16 March 1750 – 9 January 1848) was a German astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigollet, which b ...

, the younger sister of

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

, independently discovered it in 1783, thinking it had not yet been catalogued by Messier.

Walter Scott Houston Walter Scott Houston (May 30, 1912–December 23, 1993) was an American popularizer of amateur astronomy. He wrote the " Deep-Sky Wonders" column in ''Sky and Telescope'' magazine from 1946 to 1993. Biography Houston was born in Tippecanoe, ...

(died 1993) described its appearance:

Some observers mention the cluster as having the shape of a starfish. With a fair-sized telescope, this is its appearance on a dull night, but four-inch refractorshows it as a typical star-studded galactic cluster.

Properties

It has a

Trumpler class An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

of , indicating it is strongly concentrated (I) with a large range in brightness (3) and is rich in stars (r). M93 is about 3,380

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 from the

solar radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957 ...

and has a great spatial radius of 10 light-years, a

tidal radius 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 , and a core radius of . Its age is estimated at 387.3 million years. It is nearly on the

galactic plane The galactic plane is the plane (geometry), plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galac ...

and has an orbit that varies between from the

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

over a period of Myr. Fifty-four

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 ...

s have been found in M93, including one

slowly pulsating B-type star A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 ...

, one

rotating ellipsoidal variable Rotating ellipsoidal variables are a class of close binary variable star systems whose components are ellipsoidal. They are not eclipsing, but fluctuations in apparent magnitude occur due to changes in the amount of light emitting area visible to ...

, seven

Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a class of pulsating star, comprising several sub-classes of object with A- or F-type spectra. The variables follow a period-luminosity ...

s, six

Gamma Doradus variable Gamma Doradus variables are variable stars which display variations in luminosity due to non-radial pulsations of their surface. The stars are typically young, early F or late A type main sequence In astronomy, the main sequence is a classifi ...

s, and one hybrid δ Sct/γ Dor pulsator. Four

spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

systems within include a yellow straggler component.

Gallery

Image:Messier object 093.jpg, Messier 93 atlas image Image:M93map.png, Finder chart for M93

References

External links

SEDS: Open Star Cluster M93
* * {{Ngc25 Messier 093 Orion–Cygnus Arm Messier 093 093 Messier 093 Astronomical objects discovered in 1781 Discoveries by Charles Messier

Observational history and appearance

Properties

Gallery

See also

References

External links