Discovery of Neptune - Discovery Observation: September 24, 1846

Discovery Observation: September 24, 1846

Le Verrier was unaware that his public confirmation of Adams' private computations had set in motion a British search for the purported planet. On 31 August, Le Verrier presented a third memoir, now giving the mass and orbit of the new body. Having been unsuccessful in his efforts to interest any French astronomer in the problem, Le Verrier finally sent his results by post to Johann Gottfried Galle at the Berlin Observatory. Galle received Le Verrier's letter on 23 September and immediately set to work observing in the region suggested by Le Verrier. Galle's student, Heinrich Louis d'Arrest, suggested that a recently drawn chart of the sky, in the region of Le Verrier's predicted location, could be compared with the current sky to seek the displacement characteristic of a planet, as opposed to a stationary star.

Neptune was discovered just after midnight, after less than an hour of searching and less than 1 degree from the position Le Verrier had predicted, a remarkable match. After two further nights of observations in which its position and movement were verified, Galle replied to Le Verrier with astonishment: "the planet whose place you have really exists" (emphasis in original). The discovery telescope was an equatorial mounted achromatic refractor by Joseph Fraunhofer's firm Merz und Mahler.