1663 van den Bos

1663 van den Bos, provisional designation, is a stony Florian asteroid and an exceptionally slow rotator from the inner regions of the asteroid belt, approximately 12 kilometers in diameter. It was discovered on 4 August 1926, by English astronomer Harry Edwin Wood at Johannesburg Observatory in South Africa. It was later named after astronomer Willem Hendrik van den Bos.

Orbit and classification
The S-type asteroid is a member of the Flora family, a large group of stony asteroids in the main-belt. It orbits the Sun at a distance of 1.8–2.6 AU once every 3 years and 4 months (1,224 days). Its orbit has an eccentricity of 0.18 and an inclination of 5° with respect to the ecliptic.

In March 2082, van den Bos will pass 29 Amphitrite at a distance of 0.0065 AU. The body's observation arc begins with a post-recovery observation taken at Johannesburg in 1936, when it was also identified as, which is a full decade after its official discovery observation from 1926.

Slow rotator
In October 2010, a rotational lightcurve of van den Bos was obtained from photometric observations by astronomers Robert Stephens and David Higgins. It gave a rotation period of 740 hours with a brightness variation of 0.80 magnitude (U=3-). It is one of the slowest rotating minor planets (see list) and a suspected tumbler, that has a non-principal axis rotation. At the same time, photometric observations at the Shadowbox Observatory gave an alternative, yet ambiguous period of 155 hours with an amplitude of 0.5 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, van den Bos measures between 7.58 and 13.54 kilometers in diameter, and its surface has an albedo between 0.171 and 0.255. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2045 and a diameter of 12.25 kilometers using an absolute magnitude of 11.9.

Naming
This minor planet was named in honor of Dutch-born, South African astronomer Willem Hendrik van den Bos (1896–1974), former director of the Union Observatory (1941–1956) and president of the Astronomical Society of South Africa (1943–1955). He made visual micrometric observations and discovered thousands of double stars. The official was published by the Minor Planet Center on 1 July 1972 (M.P.C. 3297).