Anders Johan Lexell (December 24, 1740 - December 11, 1784)

Anders Johan (sometimes in Russian: Andrei Ivanovich) Lexell was born on December 24, 1740 in Abo, then Sweden (now Turku, Finland), where he lived until 1763, and graduated at the university of Abo im 1760. In 1763, he became assistant professor at Uppsala Nautical School, in 1766 professor of mathematics. In 1768 he was invited to the St. Petersburg Academy of Science where he was appointed as professor of astronomy in 1771, and in succession of Euler, to the chair of mathematics in 1783. He died at St. Petersburg a year later, on December 11, 1784. From 1780 to 1782 he had undertaken a travel through Europe and visited Germany, France and England.

Besides significant work in mathematics, mainly analysis and geometry, he contributed to astronomy his calculation of the solar parallax and the calculation of the orbits of several comets. Among these comets was one discovered by Charles Messier, the first for which a short period (5 1/2 years) was found. Lexell also found that it had passed very close to Jupiter and its moons, but while the comet changed its orbit significantly and could not be found later, the moons were uneffected; this led him to the conclusion that the comet's mass was extremely low.

He also was among the first to calculate an orbit for planet Uranus as it was newly discovered by William Herschel on March 13, 1781.

Lexell was honored in 1935 by naming Moon crater Lexell (35.8 S, 4.2 W, 62 km diam) after him.



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