Anders Johan Lexell (December 24, 1740 – December 11, 1784 (Julian calendar: November 30)) was a Swedish-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. December 24 is the 358th day of the year in the Gregorian Calendar (359th in leap years). ... Events May 31 - Friedrich II comes to power in Prussia upon the death of his father, Friedrich Wilhelm I. October 20 - Maria Theresia of Austria inherits the Habsburg hereditary dominions (Austria, Bohemia, Hungary and present-day Belgium). ... December 11 is the 345th day (346th in leap years) of the year in the Gregorian calendar. ... 1784 was a leap year starting on Thursday (see link for calendar). ... The Julian calendar was introduced by Julius Caesar in 46 BC, taking force in 45 BC or 709 ab urbe condita. ... November 30 is the 334th day (335th on leap years) of the year in the Gregorian calendar, with 31 days remaining, as the final day of November. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... A mathematician is a person whose area of study and research is mathematics. ...

He emigrated to Russia in 1768. He studied the motions of comets. He computed the orbit of comet D/1770 L1 (Lexell), 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 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. 1768 was a leap year starting on Friday (see link for calendar). ... Comet Hale-Bopp, showing a white dust tail and blue gas tail (February 1997) A comet is a small astronomical object similar to an asteroid but composed largely of ice. ... Charles Messier Charles Messier (June 26, 1730 – (April 12, ]) was a French astronomer who in 1774 published a catalogue of 45 deep sky objects such as nebulae and star clusters. ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ... An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earths orbit and which may therefore pose a collision danger. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... 1767 was a common year starting on Thursday (see link for calendar). ... 1779 was a common year starting on Friday (see link for calendar). ... Mosaic of Solar System planets except Pluto, including Earths Moon (not to scale). ...

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. Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1. ... A planet (from the Greek πλανήτης, planētēs which means wanderer or more forcefully vagrant, tramp) is an object in orbit around a star that is not a star in its own right. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... Urbain Le Verrier. ...

The asteroid 2004 Lexell is named in his honour.

External links

• Biography
• Comet Lexell