Anders Johan Lexell

Anders Lexell
Silhouette by F. Anting (1784)
Born	(1740-12-24)24 December 1740 Åbo, Finland
Died	11 December 1784(1784-12-11) (aged 43) [OS: 30 November 1784] St. Petersburg, Russian Empire
Nationality	Swedish
Alma mater	The Royal Academy of Turku
Known for	Calculated the orbit of Lexell's Comet Calculated the orbit of Uranus
Scientific career
Fields	Mathematician Physicist Astronomer
Institutions	Uppsala Nautical School Imperial Russian Academy of Sciences
Doctoral advisor	Jakob Gadolin
Other academic advisors	M. J. Wallenius

Anders Johan Lexell (24 December 1740 – 11 December [O.S. 30 November] 1784) was a Finnish-Swedish astronomer, mathematician, and physicist who spent most of his life in Imperial Russia, where he was known as Andrei Ivanovich Leksel (Андрей Иванович Лексель).

Lexell made important discoveries in polygonometry and celestial mechanics; the latter led to a comet named in his honour. La Grande Encyclopédie states that he was the prominent mathematician of his time who contributed to spherical trigonometry with new and interesting solutions, which he took as a basis for his research of comet and planet motion. His name was given to a theorem of spherical triangles.

Lexell was one of the most prolific members of the Russian Academy of Sciences at that time, having published 66 papers in 16 years of his work there. A statement attributed to Leonhard Euler expresses high approval of Lexell's works: "Besides Lexell, such a paper could only be written by D'Alambert or me".^[1] Daniel Bernoulli also praised his work, writing in a letter to Johann Euler "I like Lexell's works, they are profound and interesting, and the value of them is increased even more because of his modesty, which adorns great men".^[2]

Lexell was unmarried, and kept up a close friendship with Leonhard Euler and his family. He witnessed Euler's death at his house and succeeded Euler to the chair of the mathematics department at the Russian Academy of Sciences, but died the following year. The asteroid 2004 Lexell is named in his honour, as is the lunar crater Lexell.