The Planet Found with a Pen
Uranus was drifting off its predicted path, as if something unseen were tugging on it. A mathematician worked out where the culprit must be, and on the first night of looking, there it was.
What was reported
After Uranus was discovered in 1781, astronomers found that it didn't move quite as predicted: something seemed to be pulling on it. The French mathematician Urbain Le Verrier, using only calculations, worked out where an unknown planet would have to be to explain it, and sent his prediction to the Berlin Observatory.
On the night of 23 September 1846, Johann Galle and Heinrich d'Arrest pointed their telescope at the spot. Within an hour, they found an object not on their star charts, less than a degree from where Le Verrier had said. It was Neptune.
Explanations offered
The discovery was a triumph of Newton's theory of gravity, showing that unseen worlds could be found by their pull alone. In England, John Couch Adams had made similar calculations, which led to a long dispute about credit. The same method later failed to find a planet 'Vulcan'.
- When
- 23 September 1846
- Where
- Berlin Observatory, Berlin, Germany
- Witnesses
- Urbain Le Verrier, Johann Galle and Heinrich d'Arrest
- Status
- Confirmed
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.
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