<-- Back to list
A lecture on Anders Johan Lexell, his life and his discoveries.

The Finnish mathematician and astronomer Anders Johan Lexell (1740–1784) was a long-time close collaborator as well as the academic successor of Leonhard Euler at the Imperial Academy of Sciences in Saint Petersburg. Lexell was initially invited by Euler from his native town of Abo (Turku) in Finland to Saint Petersburg to assist in the mathematical processing of the astronomical data of the forthcoming transit of Venus of 1769. A few years later he became an ordinary member of the Academy. This is the first-ever full-length biography devoted to Lexell and his prolific scientific output. His rich correspondence especially from his grand tour to Germany, France and England reveals him as a lucid observer of the intellectual landscape of enlightened Europe. In the skies, a comet, a minor planet and a crater on the Moon named after Lexell also perpetuate his memory (Source:

Lexell also was the first to compute the orbit of Uranus and to actually prove that it was a planet rather than a comet.[18] He made preliminary computations while travelling in Europe in 1781 based on Hershel's and Maskelyne's observations. Having returned to Russia, he computed the orbit more precisely based on new observations, but due to the long orbital period it was still not enough data to prove that the orbit was not parabolic. Lexell then found the record of a star observed in 1759 by Christian Mayer in Pisces that was neither in the Flamsteed catalogues nor in the sky by the time Bode sought it. Lexell presumed that it was an earlier sighting of the same astronomical object and using this data he calculated the exact orbit, which proved to be elliptical, and proved that the new object was actually a planet. In addition to calculating the parameters of the orbit Lexell also estimated the planet's size more precisely than his contemporaries using Mars that was in the vicinity of the new planet at that time. Lexell also noticed that the orbit of Uranus was being perturbed. He then stated that, based on his data on various comets, the size of the Solar system can be 100 AU or even more, and that it could be other planets there that perturb the orbit of Uranus (Source: Wikipedia)

Johan Stén is the author of A Comet of Enlightenment
View via Facebook page -->