You may not have heard of him, but in his time French mathematician Urbain Le Verrier was famous and respected—at least among astronomers. After all, he had just lounged about doing mathematics and had discovered an entire planet! A big one, too!
(In 1846, Le Verrier predicted the presence and orbit of Neptune and persuaded some astronomers to look for it at the right place. When it was found, Le Verrier was given credit for the discovery of Neptune.)
More than a decade later, Le Verrier announced that there was an anomaly in Mercury's orbit—a small difference between what the mathematical equations previously laid out by Sir Isaac Newton said Mercury should be doing in its orbit, and what was actually observed by astronomers watching Mercury night after night. Le Verrier said that there could several explanations for the anomaly—one of which was another planet that was so close to the Sun that it was very difficult to observe.
On this date in 1860, Le Verrier announced the discovery of such a planet. He named the planet Vulcan, and he announced it to members of the Académie des Sciences with the words, “Gentlemen, I give you the planet Vulcan!”
Le Verrier had once again used mathematics to compute where the new planet should be, and he had consulted with amateur astronomer Edmond Modeste Lescarbault, who had apparently spotted the planet in the right place, making a transit across the face of the Sun.
|This is a transit of Mercury.|
(We can sometimes see the planets that are closer to the Sun than Earth, Venus and Mercury, as they cross the face of the Sun. They look like small black dots, and they cross the disk of the Sun in five or six hours. These crossings are called “transits.”)
|This is a sunspot.|
The problem with this announcement is, Lescarbault was wrong—apparently he was seeing a sunspot seem to move across the Sun as the Sun revolved on its axis. And so that made Le Verrier's announcement wrong, too. Many astronomers tried to confirm the so-called sightings and failed, and eventually Einstein's refinement to Newtonian physics explained the anomaly of Mercury's orbit without the need of another planet.
Also on this date: