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How did Johann Gottfried Galle and Heinrich Louis d’Arrest identify Neptune?

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Clouds in Neptune's atmosphere — Neptune A photograph of clouds in Neptune's atmosphere, taken by Voyager 2 in August 1989. The view is from below the planet's equator, and north is up. The Great Dark Spot (center left) is 13,000 km (8,100 miles)—about the diameter of Earth—in its longer dimension. Accompanying it are bright, wispy clouds thought to comprise methane ice crystals. At higher southern latitudes lies a smaller, eye-shaped dark spot with a light core (bottom left). Just above that spot is a bright cloud dubbed Scooter. Each of these cloud features was seen to travel eastward but at a different rate, the Great Dark Spot moving the slowest.

Johann Gottfried Galle and Heinrich Louis d’Arrest identified Neptune on September 23, 1846, by utilizing precise mathematical predictions provided by the French astronomer Urbain-Jean-Joseph Le Verrier.12

Le Verrier had calculated the planet's expected position based on the observed orbital irregularities of Uranus. Upon receiving these coordinates, Galle and d’Arrest—working at the Berlin Observatory—were able to conduct a highly efficient search because they possessed detailed star maps that were not available to other astronomers attempting the same task.12

Using these maps, they identified an object that did not appear on their charts, marking it as an uncharted star. They confirmed the discovery the following night by observing that the object had shifted its position relative to the background stars, thereby verifying it was a planet. While Galle and d’Arrest were the first to visually identify the planet, the scientific credit for the discovery is primarily attributed to the mathematical work of Le Verrier and, to a lesser extent, the British mathematician John Couch Adams.23