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Johann Gottfried Galle (1812 - 1910)

Johann Galle was a German astronomer who started work as assistant to Johann Franz Encke at the Berlin Observatory in 1835. Galle's PhD thesis, finished in 1845, was a critic of Ole Romer's 1706 observations of Uranus. Galle sent a copy of his thesis to Urbain Le Verrier in Paris and, one year later, Le Verrier's reply was received. Le Verrier's letter suggested that Galle point his telescope at a specific section of the sky over a certain period of time. He predicted that a new planet would be found. Galle asked permission from Encke to use the observatory telescope and, on the given night, Galle and a Danish astronomer, Henrich Louis d'Arrest, set to work. Galle used the telescope and d'Arrest studied the star charts. Not too long into their search, the new planet had been found.

Although Galle is often credited with the discovery of planet Neptune, if it had not been for the mathematicians, he would never have known where to look to find it. In fact, Galle was not the first to observe the planet. Galileo had recorded it, as had the astronomers John Herschel, Lalande and Von Lamont. However, when it had been previously observed, it had been recorded erroneously as a star.

 

Johann Galle

Johann Gottfried Galle.
© Deusches Museum.

 

In fact, the credit for the discovery of the planet Neptune probably belongs to two mathematicians; John Crouch Adams in England and Urbain Le Verrier in France. Both men were working on the same problem independently. They were investigating the reason for the perturbations in the orbit of the planet Uranus. Using Newton's laws of gravity they correctly predicted that the small irregularities observed in Uranus's orbit was most probably due to another planet, as yet unidentified. They even manage to work out the orbit of Planet X which meant that they could predict where and when it would appear in the sky.

Adams was one year ahead of Le Verrier in his work. However, the Director of the Cambridge Observatory, James Callis, had first refused to look for the new planet and, consequently, missed the chance of the discovery. It was Galle, following instructions from Le Verrier who took the credit.

The British astronomer, John Herschel, refuted the French claim that Le Verrier had calculated the planet's position by declaring that Adams had done so months before. The French were furious. The Royal Academy was equally furious with James Callis and the Royal Astronomer, George Airy, for not seeking out the planet when Adams had asked them to!

As for Johann Galle, in 1851 he took up the post of Professor of Astronomy and Director of the Observatory in Breslau (now Wroclaw), in Poland. His son Andreas worked as his assistant and, together, they published a list of 414 comets in 1894. Galle had discovered three of these. He is also credited with discovering the crêpe ring of Saturn. He has a moon crater named after him as well as Neptune's ring.

 

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