1585 Union, provisional designation 1947 RG, is a dark background asteroid from the outer regions of the asteroid belt, approximately 52 kilometers in diameter. It was discovered on 7 September 1947, by South African astronomer Ernest Johnson at the Union Observatory in Johannesburg, South Africa.^[13] The asteroid was named after the discovering observatory.^[2]

Union is not a member of any known asteroid family. It orbits the Sun in the outer main belt at a distance of 2.0–3.8 AU once every 5.01 years (1,830 days). Its orbit has an eccentricity of 0.31 and an inclination of 26° with respect to the ecliptic.^[1]

In 1929, the asteroid was first identified as 1929 DB at the Uccle Observatory in Belgium. The body's observation arc begins at the Finnish Turku Observatory in February 1939, more than 17 years prior to its official discovery observation at Johannesburg.^[13]

Union has been characterized as a P-type asteroid by the Wide-field Infrared Survey Explorer (WISE), while the LCDB assumes a generic carbonaceous C-type.^[3][9]

This minor planet was named after the discovering Union Observatory, also known as the Johannesburg Observatory, Transvaal Observatory (1909–1912) and Republic Observatory (1961–1971). The official naming citation was published by the Minor Planet Center in June 1953 (M.P.C. 941).^[14]