940?-1000

Central Asian astronomer and mathematician who calculated the latitude for the city of Rayy, near modern Tehran, Iran, and developed a relatively accurate sextant. Born in what is now Tajikistan, al-Khujandi was a Mongol, but spent most of his career in Arab lands controlled by the Buyid dynasty, who seized control of the Abbasid capital at Baghdad in 940. Working at the observatory in Rayy, al-Khujandi developed a large mural sextant that indicated seconds, providing a level of accuracy beyond that of most existing instruments. He also calculated the obliquity of the ecliptic with less than perfect accuracy, and is sometimes incorrectly credited with discovering the sine theorem.