German astronomer Johann Gottfried Galle, with assistance from Heinrich Louis d’Arrest, made the first telescopic observations of Neptune, the eighth planet in the Solar System, on this date in 1846. Neptune had been mathematically predicted to exist since 1781, as irregularities in the orbit of Uranus were observed and theories of a planet whose orbit was outside Uranus’ were postulated. Also, there is evidence that Neptune was observed as far back as 1612 (by Galileo), 1795 (by Lalande), and 1830 (by Herschel), but none recognized it as a planet.

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