Urbain Le Verrier ( March 11 , 1811 â `` September 23 , 1877 ) was a French mathematician who was famous for co-discovering the planet , Neptune . Urbain Jean Joseph Le Verrier ( 11 March 1811 â `` 23 September 1877 ) was a French mathematician who specialized in celestial mechanics and is best known for his part in the discovery of Neptune .