Ursa Major I Dwarf (UMa I dSph) is a dwarf spheroidal galaxy orbiting the Milky Way galaxy. The discovery by Beth Willman et al. was announced in 2005.[2]
Being a small dwarf galaxy, it measures only a few thousand light-years in diameter. As of 2006, it is the second least luminous galaxy known (discounting dark galaxies such as VIRGOHI21 in the Virgo cluster of galaxies), to the Boötes Dwarf (absolute magnitude -5.7). The absolute magnitude of the galaxy is estimated to be only -6.75,[2] meaning that it is less luminous than some stars, like Deneb in the Milky Way. It is comparable in luminosity to Rigel. It has been described as similar to the Sextans Dwarf Galaxy.[2] 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.[2] That is about twice the distance to the Large Magellanic Cloud; the largest and most luminous satellite galaxy of the Milky Way.
There was another object called Ursa Major Dwarf, discovered by Edwin Hubble in 1949.[3] It was designated as Palomar 4. Due to its peculiar look, it was temporary suspected to be either a dwarf spheroidal or elliptical galaxy. However, it has since been found to be a very distant (about 360,000 ly) globular cluster belonging to our galaxy.
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