
For most of the history of mankind, humans could see with their naked eyes five wandering points of light in the sky. These were the planets Mercury, Venus, Mars, Jupiter and Saturn. But with the power of a new invention called the telescope, William and Caroline Herschel discovered another wanderer, Uranus, in 1781. Astronomers then tried to predict the orbit of Uranus, and were reasonably successful using the mathematics of Newton and telescopes of their time, but they were always a little bit off. The reason, they felt, was another planet exerting a gravitational pull on Uranus. Mathematicians
John Adams of Great Britain and
Urbain Le Verrier both attacked the problem and independently, and unknown to each other, predicted the location of the new planet. However, for a short period of time, astronomers were too stubborn to look in the specified location. Adams and Le Verrier tried in vain to get their own country’s astronomers to look in the specified location. Finally German astronomer Johann Galle, after receiving mail from Le Verrier, looked in the
position specified by Le Verrier and after 30 minutes of searching on September 23, 1846, found a star not on previous star maps. They confirmed the next day that it had moved slightly, indicating that
Galle had indeed found a new planet.
The countries of the two mathematicians involved, already fierce rivals in other arenas, got into a rather nasty spat over who should get credit for the discovery, Adams or Le Verrier, and who would be allowed to name the new planet.
In an interesting sidelight, Neptune was first observed, and almost discovered over two centuries earlier. Shortly after the invention of the telescope, Italian astronomer
Galileo Galilei turned this new invention to the skies. He was fascinated by the newly discovered moons of Jupiter, and he recorded some stars in the background. One of them was Neptune. In fact, in 1613 Galileo actually noted that one of the stars had moved slightly from one night to the next. Had the skies not been overcast on the third night, he most likely would have became aware that he was not observing a star, but a new planet. Galileo’s notes of this amazing observation can be seen
here.