On the night of September 23rd, 1846, the German Astronomer Johann Gottfried Galle confirmed the discovery of the planet Neptune, which had been predicted by the French Mathematician Urban le Verrier, based on nothing but numbers.

It was one of the great triumphs of 19th century science.

Le Verrier discovered Neptune – which cannot be seen except with a strong telescope, of which there were few at the time – by observing its gravitational effect on the planet Uranus. He theorised that there must be another planet sized object in the vicinity, and worked out where it would be, mathematically.

On the 23rd of September, Galle went looking with his telescope, and found Neptune, less than one degree away from where Le Verrier had predicted it would be.

For his achievement, Le Verrier has been honoured in the heavens – craters on the moon, and mars, are named after him. And one of Neptune’s faint rings is called “The LeVerrier ring”.

Neptune, discovered by maths, on this day, September 23rd, 1846.