  anders johan lexell (24 december 1740 &ndash; 11 december 1784 (julian calendar: november 30)) was a finnish-swedish astronomer, mathematician, and physicist who spent most of his life in russia, where he is known as andrei ivanovich leksel (ÐÐ½Ð´ÑÐµÐ¹ ÐÐ²Ð°Ð½Ð¾Ð²Ð¸Ñ ÐÐµÐºÑÐµÐ»Ñ). lexell made important discoveries in polygonometry and celestial mechanics; the latter led to a comet named in his honour. la grande encyclopÃ©die states that he was the prominent mathematician of his time who contributed to spherical trigonometry with new and interesting solutions, which he took as a basis for his research of comet and planet motion. his name was given to a theorem of spherical triangles. lexell was one of the most prolific members of the russian academy of sciences at that time, having published 66 papers in 16 years of his work there. a statement attributed to leonhard euler expresses high approval of lexell's works: "besides lexell, such a paper could only be written by d'alambert or me". daniel bernoulli also praised his work, writing in a letter to johann euler "i like lexell's works, they are profound and interesting, and the value of them is increased even more because of his modesty, which adorns great men". lexell was unmarried, and kept up a close friendship with leonhard euler and his family. he witnessed euler's death at his house and succeeded euler to the chair of the mathematics department at the russian academy of sciences, but died the following year. the asteroid 2004 lexell is named in his honour, as 
1740_births 1784_deaths 18th-century_Russian_mathematicians 18th-century_astronomers 18th-century_mathematicians Finnish_astronomers Full_Members_of_the_St_Petersburg_Academy_of_Sciences Geometers Imperial_Russian_astronomers Members_of_the_French_Academy_of_Sciences Members_of_the_Royal_Swedish_Academy_of_Sciences Russian_people_of_Swedish_descent Transit_of_Venus