Ursa Major cluster [`ǝr·sǝ `mā·jǝr ´klǝs·tǝr] ASTRONOMY 1. A group of about 126 stars, including 5 stars of the constellation Ursa Major; the sun is passing through this cluster which occupies a spherical space of about 450 light-years in diameter. 2. A cluster of galaxies in the constellation Ursa Major having a redshift of about 0.051. |