Discovery of Neptune

Johann Friedrich Galle

Johann Galle Encke was given an assistant for the new Observatory and the post was filled by Johann Friedrich Galle. In 1845, Galle sent his doctoral thesis to Le Verrier, director of the Paris Observatory, and Le Verrier had sent back details of his calculations of a new planet based on perturbations of Uranus. Within one hour of starting a search for this planet, on 23. September 1846, Galle and his colleague Heinrich d'Arrest had found the planet, 8 minutes of arc away from the predicted position (they had found it because it was absent from Encke's charts). The Fraunhofer telescope used to discover Neptune is now on display in the Deutsches Museum, München.

Apparently, Galle was also the first to identify the Crepe ring (Ring C) around Saturn, in 1838, although it was forgotten and re-discovered independently a few years later. In 1875, although by this time at Breslau, he was the first person to use an asteroid (Flora) to measure the distance to the Sun, calculating a value of 148.290 million kilometers.

Heinrich D'Arrest

Heinrich D'Arrest

Soon after his part in the Neptune discovery, he discovered Comet D'Arrest on June 28. 1851, while working at the Leipzig Observatory. It was described as very faint. The comet was not found on the next night because the sky was too hazy, but on June 30, d'Arrest described it as large and faint.

The Comet has the designation 6P, and has a period of 6.2 years.

Discovery of Neptune

The Berlin discovery is covered directly above, under Galle and D'Arrest.

A couple of weeks later (by October 10), the main satellite of Triton was discovered in Liverpool by William Lassell. It is a matter of conjecture as to whether Lassel could have found the planet himself if he had acted differently.

If we are to take the words of a few ex-Cambridge University graduates at face value, they 'cherish' the memory of Professor Challis, who 'probably' saw Neptune before the Germans but didn't realise it, and through a comedy of errors (and/or incompetence) failed to look carefully where the British mathematician John Couch Adams had told him to.