731 Sorga (prov. designation: or ) is a highly elongated background asteroid from the outer regions of the asteroid belt, approximately in diameter. It was discovered on 15 April 1912, by German astronomer Adam Massinger at the Heidelberg-Königstuhl State Observatory in southwest Germany. The C-type (CD) and X-type asteroid (Xe) has a rotation period of 8.2 hours. It was named Sorga, meaning "the heavens" in the Indonesian language. Orbit and classification Sorga is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. It orbits the Sun in the outer asteroid belt at a distance of 2.6–3.4 AU once every 5 years and 2 months (1,886 days; semi-major axis of 2.99 AU). Its orbit has an eccentricity of 0.14 and an inclination of 11° with respect to the ecliptic. The body's observation arc begins at Heidelberg Observatory on 21 October 1919, more than seven years after its official discovery observation. Naming This minor planet was named Sorga, the word for "the heavens" in the Indonesian language, also transliterated as "surga". The was not mentioned in The Names of the Minor Planets by Paul Herget. Physical characteristics In the Tholen classification, Sorga is closest to a common, carbonaceous C-type asteroid and somewhat similar to a dark D-type asteroid (CD), while in the Bus–Binzel SMASS classification, it is an Xe-subtype which transitions from the X-type to the bright E-type. Sorga has also been classified as a metallic M-type asteroid. Rotation period and poles In April 2005, a rotational lightcurve of Sorga was obtained from photometric observations by Brian Warner at his Palmer Divide Observatory in Colorado. Analysis gave a classically shaped bimodal lightcurve with a well-defined rotation period of () hours and a high brightness variation of () magnitude, indicative of its elongated shape (). In February 2009, Warner revisited Sorga and determined a very similar period of () hours though with a much lower amplitude of () magnitude (). In January 2010, astronomers at the Palomar Transient Factory measured a period of hours with an amplitude of magnitude (). Additional observations by Christophe Demeautis in September 2017, and by Bruno Christmann in April 2020, gave a period of () and () hours with an amplitude of and magnitude, respectively (). In 2016, a modeled lightcurve rendered a concurring sidereal period of hours using data from the Uppsala Asteroid Photometric Catalogue, the