Neptune was discovered using mathematics. Before 1845, Uranus was widely believed to be the most distant planet. However, astronomers observed that Uranus was not always in the position predicted for it. The astronomers concluded that the gravitational attraction of a more distant planet was disturbing the orbit of Uranus.

In 1845, John Couch Adams, an English astronomer, calculated the location of this more distant planet. Urbain Leverrier, a French mathematician, independently did similar calculations. In 1846, John G. Galle and Heinrich d'Arrest of the Urania Observatory in Berlin, looked for the planet where Leverrier and Adams predicted it would be located. They saw the planet, which was later named Neptune, on September 23, 1846. Galileo, the noted Italian astronomer, may have been the first to see Neptune in 1613. However, Galileo did not recognize what he saw as a planet.

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