9936 Al-Biruni, provisional designation 1986 PN₄, is a carbonaceous asteroid from the outer region of the asteroid belt, approximately 24 kilometers in diameter. It was discovered on 8 August 1986, by Belgian and Bulgarian astronomers Eric Elst and Violeta Ivanova at the Rozhen Observatory, located in Bulgaria's Smolyan province near the border to Greece.^[9] It was named for Persian medieval scholar Al-Biruni.^[3]

Al-Biruni orbits the Sun in the outer main-belt at a distance of 2.5–3.7 AU once every 5 years and 5 months (1,976 days). Its orbit has an eccentricity of 0.19 and an inclination of 15° with respect to the ecliptic.^[1] It was first identified as 1981 UV₁₂ at Crimea-Nauchnij in 1981, extending the body's observation arc by 5 years prior to its official discovery at Rozhen.^[9]

A rotational lightcurve of Al-Biruni was obtained from photometric observations made at the U.S. Goodsell Observatory (741), Minnesota, in August 2002. The lightcurve gave a rotation period of 10.704±0.010 hours with a brightness amplitude of 0.14 in magnitude (U=2)^[8]

According to the space-based surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Al-Biruni measures between 23.9 and 27.8 kilometers in diameter, and its surface has a corresponding albedo of 0.048 to 0.065.^[5][6][7] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for carbonaceous asteroids of 0.057 and calculates a diameter of 22.2 kilometers with an absolute magnitude of 12.0.^[4]

The minor planet was named after the Persian scholar and polymath Al-Biruni (973–1048). Regarded as the founder of Indology and the father of geodesy, he made important contributions to anthropology, mathematics and astronomy. In particular, he is known for developing a method for the summation of series, for solving algebraic equations, and for the triangulation of distances on Earth's surface.^[3] The official naming citation was published by the Minor Planet Center on 26 September 2007 (M.P.C. 60728).^[10] The lunar crater Al-Biruni is also named in his honour.