Anders Johan Lexell

Anders Johan Lexell (24 December 1740 to 11 December 1784 in the new style calendar) was a Swedish-speaking Finnish astronomer, mathematician and physicist who spent most of his life in Imperial Russia, where he was known as Andrei Ivanovich Leksel. Born in Turku, he made important discoveries in polygonometry and celestial mechanics, the latter leading to a comet being named after him, and he contributed new solutions in spherical trigonometry, which he used in studying the motion of comets and planets. A theorem on spherical triangles bears his name. One of the most prolific members of the Russian Academy of Sciences, he published 66 papers there in sixteen years, and he was a close friend of Leonhard Euler and his family, witnessed Euler's death and succeeded him in the academy's chair of mathematics. He is regarded as the first Finnish-born researcher to make a significant international contribution to mathematics and astronomy. An asteroid and a lunar crater carry his name.