Leverrier, Urbain Jean Joseph (ürbăNˈ zhäN zhôzĕfˈ ləvĕryāˈ) [key], 1811–77, French astronomer who made calculations that led to the discovery of the planet Neptune. In considering the perturbations of Uranus, Leverrier made calculations indicating the presence of an unknown planet in an orbit outside that of Uranus. At the time, this was considered the crowning achievement of mathematical astronomy. The same conclusion had been reached by John Couch Adams a little earlier but had not been published, so Leverrier was initially given sole credit for the discovery of Neptune, which was actually first observed, as a result of Leverrier's instructions, by Johann Galle in 1846. After much controversy both Adams and Leverrier were honored as responsible for the planet's discovery. In 1854, Leverrier became director of the Paris Observatory.
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