1646 Rosseland

1646 Rosseland, provisional designation, is a stony asteroid from the inner regions of the asteroid belt, approximately 12 kilometers in diameter. It was discovered on 19 January 1939, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland. It was later named after Norwegian astrophysicist Svein Rosseland.

Orbit and classification
The S-type asteroid orbits the Sun in the inner main-belt at a distance of 2.1–2.6 AU once every 3 years and 8 months (1,324 days). Its orbit has an eccentricity of 0.12 and an inclination of 8° with respect to the ecliptic. Rosseland was first observed at Johannesburg Observatory as, extending the body's observation arc by 2 years prior to its official discovery observation in 1939.

Photometry
American astronomer Richard Binzel obtained the first rotational lightcurve of Rosseland in the early 1980s. It gave a rotation period of 69.2 hours with a brightness variation of 0.13 magnitude (U=2). During a survey of presumed slow rotators, photometric observations by Brazilian Cláudia Angeli and colleges gave a period of 69.2 hours and an amplitude of 0.45 magnitude (U=1).

Diameter and albedo
According to the surveys carried out by the Japanese Akari satellite and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Rosseland measures between 11.48 and 13.49 kilometers in diameter and its surface has an albedo between 0.18 and 0.2253. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 12.85 kilometers with an absolute magnitude of 11.82.

Naming
This minor planet was named in honor of renowned Norwegian astrophysicist Svein Rosseland (1894–1985), founder and first director of the Institute for Theoretical Astrophysics in Oslo. His work on the theory of stellar interiors included studies of stellar rotation and stability and the derivation of the Rosseland mean opacity. The lunar crater Rosseland is also named after him. The official was published by the Minor Planet Center on 20 February 1976 (M.P.C. 3932).