1781 Van Biesbroeck

1781 Van Biesbroeck (prov. designation: ) is a Vesta asteroid from the inner regions of the asteroid belt, approximately 8.5 kilometers in diameter. It was discovered on 17 October 1906, by German astronomer August Kopff at Heidelberg Observatory in southern Germany. It was named after astronomer George Van Biesbroeck.

Orbit and classification
Van Biesbroeck orbits the Sun in the inner main-belt at a distance of 2.1–2.7 AU once every 3 years and 9 months (1,354 days). Its orbit has an eccentricity of 0.11 and an inclination of 7° with respect to the ecliptic. It is not known whether the member of the Vesta family of asteroids is in fact a V/J-type, or if it is an unrelated interloper, as currently assumed to be more likely. The asteroid's observation arc begins with its official discovery observation, as no precoveries were taken, and no previous identifications were made.

Physical characteristics
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Van Biesbroeck measures 8.5 kilometers in diameter, and its surface has an albedo of 0.203. A generic absolute magnitude-to-diameter conversion gives an inferred diameter between 8 and 14 kilometers, assuming an albedo in the range of 0.05 to 0.25 for an absolute magnitude of 12.8. As of 2017, Van Biesbroeck's composition, rotation period and shape remain unknown.

Naming
This minor planet was named after renowned Belgian–born observational astronomer George Van Biesbroeck, who naturalized as U.S. citizens in 1922. He specialized in the observation of double stars, variable stars, comets and asteroids, of which he discovered sixteen at the U.S. Yerkes Observatory in Williams Bay, Wisconsin, between 1922 and 1939. The official was published by the Minor Planet Center on 1 January 1974 (M.P.C. 3569).

In 1961, he published the Van Biesbroeck's star catalog of low-mass, low-luminosity stars. The mountain Van Biesbroeck near the McDonald Observatory, the lunar crater Van Biesbroeck, and most notably the red dwarf Van Biesbroeck's Star, were also named in his honour. (There are very few stars named after people). The George Van Biesbroeck Prize, awarded by the American Astronomical Society for achievements in astronomy, also bears his name.