## 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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