NGC 1931 open star cluster. An open star cluster is a loose grouping of stars within a galaxy. The closest open star cluster to Earth is the Hyades open star cluster, which is 150 light years away and in the constellation of Taurus. NGC 1931 is located in the constellation of Auriga, just west of the M36 star cluster, about 10,000 light years from earth. It is a relatively small, young open star cluster and reflection nebula, with a core of new white hot stars. Over time, due to the gravitational forces exerted by other stars in the galaxy, the stars of an open star cluster will drift apart.