Ursa Major I Dwarf (UMa I dSph) is a

dwarf spheroidal galaxy A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are com ...

that

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy. It was discovered in 2005 within the

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

constellation and is the third least luminous known galaxy.

Discovery

It was discovered by Beth Willman, Julianne J. Dalcanton, David Martinez-Delgado, and Andrew A. West in 2005.

Properties

Being a small

dwarf galaxy A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

, it measures only a few thousand light-years in diameter. As of 2006, it is the third least luminous galaxy known (discounting possible dark galaxies such as VIRGOHI21 in the

Virgo cluster The Virgo Cluster is a large cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo. Comprising approximately 1,300 (and possibly up to 2,000) member galaxies, the cluster forms the heart of the la ...

of galaxies), after the Boötes Dwarf (absolute magnitude −5.7) and the more recently discovered

Ursa Major II Dwarf Ursa Major II Dwarf (UMa II dSph) is a dwarf spheroidal galaxy situated in the Ursa Major constellation and discovered in 2006 in the data obtained by the Sloan Digital Sky Survey. The galaxy is located approximately 30 kpc from the Sun and ...

(absolute magnitude −3.8). The

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...

of the galaxy is estimated to be only −6.75, meaning that it is less luminous than some stars, like Deneb in the Milky Way. It is comparable in luminosity to

Rigel Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand ...

. It has been described as similar to the Sextans Dwarf Galaxy. Both galaxies are ancient and metal-deficient. It estimated to be located at a distance of about 330,000 light-years (100 kpc) from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. That is about twice the distance to the Large Magellanic Cloud; the largest and most luminous satellite galaxy of the Milky Way.

Related objects

There was another object called "Ursa Major Dwarf", discovered by Edwin Hubble in 1949. It was designated as Palomar 4. Due to its peculiar look, it was temporarily suspected to be either a dwarf spheroidal or

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

. However, it has since been found to be a very distant (about 360,000 ly)

globular cluster 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 ...

belonging to our galaxy. The

was discovered in 2006 in the Ursa Major constellation and is also extraordinarily dim.

References

External links

* {{Sky, 10, 34, 52.8, +, 51, 55, 12, 330000 Dwarf spheroidal galaxies Local Group Milky Way Subgroup Ursa Major (constellation) ?

Discovery

Properties

Related objects

See also

References

External links