Lexell, Anders Jean

(in Russian, Leksel’, Andrei Ivanovich). Born Dec. 24, 1740, in Äbo, Finland, of Swedish parents; died Nov. 30, 1784, in St. Petersburg. Russian astronomer. Academician of the St. Petersburg Academy of Sciences (1771).

Lexell came to St. Petersburg in 1768 and began working under the direction of L. Euler. Lexell calculated the orbits of the comets 1769 and 1770 I and showed that the perturbing influence of the planet Jupiter was the cause of the radical change in the orbit of comet 1770 I. He also determined that the new celestial object discovered by W. Herschel in 1781 was not a comet, as Herschel assumed, but the planet Uranus. By investigating the irregularities in its motion, Lexell concluded that a still more distant planet existed.