Anders Johan Lexell
Anders Johan Lexell ( born December 24, 1740 in Turku, † December 11 1784 in St. Petersburg, according to Julian Calendar 30 November) was a Swedish -born finland, later emigrated to Russia astronomer and mathematician. The Russian spelling of his name is Andrei Ivanovich Leksel ( Андрей Иванович Лексель ). Other spelling variations are Anders Johann Lexell Anders Johann Lexell or.
Life and work
Lexell was born in Åbo ( Turku today ), the son of Johan Lexell, an administrative officer, and Madeleine -Catherine Björkegren. At his birth time, the city of the Swedish kingdom and his parents belonged were members of the Swedish population in Finland. After studying at the Academy at Åbo he received his doctorate with the thesis " Aphorismi mathematico - physici " Doctor of Philosophy. His doctor father was Jacob Gadolin. In 1763 he moved to Uppsala and taught as a mathematics lecturer at the local university and from 1766 as a professor of mathematics at the navigation school in Uppsala. With the work " Methodus integrandi nonnulis aequationum exemplis illustrata " Lexell was appointed in 1768 at the suggestion of Leonhard Euler as an adjunct professor to Saint Petersburg. In 1771 he became a full member of the Russian Academy of Sciences. 1780-81 he undertook a study tour of Germany, France, the Netherlands, England and Sweden. In St. Petersburg, he was a close friend of Leonhard Euler and, after his death in 1783, his successor in St. Petersburg, but died only a year later.
Lexells main area of work was the celestial mechanics. He calculated the movements of comets and other celestial bodies. In 1769 he examined together with Christian Mayer in St. Petersburg the transit of Venus. This made it possible to invoice the parallax of the sun. He calculated the orbit of the comet D/1770 L1 ( Lexell ), which was then named after him, although he was discovered by Charles Messier. This comet came the earth from all comets closest to only some asteroid came even closer. Comet Lexell was characterized for the first near-Earth object; its exact distance is not measured, but it is thought that he flew past at a distance of not more than 3 million kilometers of the Earth.
Lexell Euler helped in the development of the lunar theory and was co-authored with Euler in 1772 published " Theoria Lunae motuum ".
Lexell was the first determined the orbit of the planet Uranus shortly after its discovery by William Herschel in 1781. He recognized that it was it not, as initially suspected a comet, but is a planet. He also realized that the motion of Uranus was disturbed by another object, and suspected as the cause of a then unknown planet, but its position could not be calculated at this time. This more than 60 years later succeeded Urbain Le Verrier, whose calculations led to the discovery of the planet Neptune.
The lunar crater Lexell and the asteroid (2004) Lexell have been named after him.