1646 Rosseland, provisional designation 1939 BG, is a stony asteroid from the inner regions of the asteroid belt, about 13 kilometers in diameter. It was discovered by Finnish astronomer Yrjö Väisälä at Turku Observatory on 19 January 1939. The S-type asteroid orbits the Sun at a distance of 2.1–2.6 AU once every 3.63 years (1,325 days). Its orbit shows an eccentricity of 0.12 and is tilted by 8 degrees to the plane of the ecliptic. It has a rotation period of 69 hours and an albedo of 0.18–0.23, according to the surveys carried out by the Akari and WISE/NEOWISE space-based missions.