Ursa Major I Dwarf, or UMa I dSph, is a dwarf spheroidal galaxy which belongs to the Local Group and is satallite of the Milky Way galaxy. It measures only a few thousand light-years in diameter. The Ursa Major Dwarf is the second least luminous galaxy known to the Boötes Dwarf (absolute magnitude -5.7). The absolute magnitude of the galaxy is estimated to be only -6.75, meaning that it is less luminous than some stars in the Milky Way. It has been described as similar to the Sextans Dwarf Galaxy. Both galaxies are ancient and metal-deficient.
Ursa Major Dwarf galaxy lies at 330,000 light-years (100 Kpc) away from the Earth; twice the distance to the Large Magellanic Cloud; the largest and most luminous satellite galaxy of the Milky Way. It was discovered by Beth Willman in 2005.
One must not mistake the other celestial object which is also called Ursa Major Dwarf, discovered by Edwin Hubble in 1949. It was designated as Palomar 4, which, due to its peculiar look, was temporary suspected to be either a dwarf spheroidal or elliptical galaxy. Nevertheless, it has since been found to be a very distant (about 360,000 ly) globular cluster belonging to our galaxy.