Anders Johan Lexell

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Anders Johan Lexell

Anders Johan Lexell (December 24, 1740 – December 11, 1784 (Julian calendar: November 30)) was a Finland-Swedish-born Russian astronomer and mathematician. In Russian he is known as Andrei Ivanovich Leksel (Андрей Иванович Лексель). His name is also given as Anders Johann Lexell or even Johann Anders Lexell.

He emigrated to Russia in 1768. He studied the motions of comets. He computed the orbit of comet "D/1770 L1" (Lexell) discovered on June 14, 1770, and it is named after him although it was discovered by Charles Messier. This comet made the closest known approach to Earth by any comet in history (although asteroids have come closer), making it the first known near-Earth object; the exact distance is not known but has been estimated to have been within 3 million km. Lexell showed that the comet had had a much larger perihelion distance until an encounter with Jupiter in 1767, and he predicted that, after encountering Jupiter again at an even closer distance two revolutions later, in 1779, it would be altogether expelled from the inner solar system.

He was also the first to compute the orbit of Uranus soon after its discovery and realized from its orbit that it was a planet rather than a comet. He also found that Uranus was being perturbed and deduced the existence of another planet (the eventual Neptune), although the position of Neptune was not calculated until much later by Urbain Le Verrier.

The asteroid 2004 Lexell is named in his honour.

[edit] Literature

Alexander Moutchnik, Forschung und Lehre in der zweiten Hälfte des 18. Jahrhunderts. Der Naturwissenschaftler und Universitätsprofessor Christian Mayer SJ (1719-1783) (Algorismus, Studien zur Geschichte der Mathematik und der Naturwissenschaften, Bd. 54), Erwin Rauner Verlag, Augsburg, 523 Seiten mit 8 Tafeln, 2006. ISBN 3-936905-16-9 Scientific Research and University Teaching in the 2nd half of the 18th century. Natural Scientist and University Professor Christian Mayer SJ (1719-1783)] Inhaltsverzeichnis: PDF