The farthest out of the four giant planets. Neptune is almost a twin of Uranus in size, mass and composition. It opened in 1846, within a specific position in the theoretically predicted was one of the greatest achievements of celestial mechanics. Difficulties in accounting for the observed motion of Uranus on perturbations from other planets, led in the early 19th century, the suspicion that a new planet beyond the orbit of Uranus, may cause deviation from the projected track. In 1845-1846, I. c. Adams in Cambridge, England, and then u. d. Leverrier in Paris solved the problem, difficult flowing mass and orbital elements of an unknown planet. Adams is not received immediate attention and Leverrier, a decision that led to the discovery of Neptune, j. Halle, Berlin, who found the planet September 23, 1846, only 55 foot from its intended position.