Neptune was discovered by means of mathematics before being seen through a telescope. Astronomers had noticed that Uranus, which they thought was the most distant planet, was not always in the position they predicted for it. The force of gravity of some unknown planet seemed to be influencing Uranus.
In 1843, John C. Adams, a young English astronomer and mathematician, began working to find the location of the unknown planet. Adams predicted the planet would be about 1 billion miles (1.6 billion kilometers) farther from the sun than Uranus. He completed his remarkably accurate work in September 1845. Adams sent it to Sir George B. Airy, the Astronomer Royal of England. However, Airy did not look for the planet with a telescope. Apparently, he lacked confidence in Adams.
Meanwhile, Urbain J. J. Leverrier, a young French mathematician unknown to Adams, began working on the project. By mid-1846, Leverrier also had predicted Neptune's position. He sent his predictions, which were similar to those of Adams, to the Urania Observatory in Berlin, Germany. Johann G. Galle, the director of the observatory, had just charted the fixed stars in the area where the planet was believed to be. On Sept. 23, 1846, Galle and his assistant, Heinrich L. d'Arrest, found Neptune near the position predicted by Leverrier. Today, both Adams and Leverrier are credited with the discovery.