On March 26, 1859, a French medical doctor and amateur astronomer named Lescarbault claimed to have observed a planet closer to the sun than Mercury. He called it Vulcan, after the Roman god of fire. He calculated the planet’s movements and sent the information onto Urbain Le Verrier, France’s most famous astronomer.
Le Verrier had already noticed that Mercury deviated from its orbit. A gravitational pull from Vulcan would fit in nicely with what he was looking for. Le Verrier checked out other reports and found out that other astronomers had also seen a small dark disc against the background of the sun. They all knew that it couldn’t be a sunspot, because sunspots travel more slowly. Le Verrier decided to pay the doctor a visit.
When Le Verrier examined Lescarbault’s telescope, he found that it was of very poor quality and that it gave distorted images. Yet the astronomer still believed that the doctor discovered a new addition to the solar system. From calculations made with this inferior equipment Le Verrier came to the conclusion that Vulcan was 13 million miles from the sun and that it took twenty days to complete its orbit.
No one could find the planet. Le Verrier said that it would be seen crossing the sun in March or April of 1860; it wasn’t. The eminent astronomer concluded that the transit happened at night when the sun was not visible. But the sun was visible on the other side of the Earth.
In March of 1862, an English amateur astronomer named Lummins claimed to have seen Vulcan. Others claimed to have seen a small comet. And a small comet would look like a tiny planet rather than a big comet.
Le Verrier explained away the controversy by saying that most of the time the planet would be lost in the sun’s glare. He said that the best time to observe Vulcan would be during a solar eclipse. The sky would be dark and the planets closer to the sun would be visible. The next eclipse would be on March 22, 1877.
Many astronomers had their eyes focused on the sun that day but no one could find the elusive planet. And what did Le Verrier’s supporters had to say? Vulcan was hiding behind the sun.
A year later, on July 29, two American astronomers observing a solar eclipse, from separate places in Wyoming and Colorado, claimed to have seen Vulcan. They said that it was red in color and that it had the shape of a small planet.
That seemed to be the proof for the existence of the planet Vulcan that the proponents had been waiting for. But, the critics pointed out, if Vulcan existed it would have to be bigger than Mercury, to affect Mercury’s orbit, about the size of Venus. A planet that big and that close to the sun would have to be the brightest planet in the sky.
The matter was not settled until Albert Einstein came along with his theory of gravitation. It proved once and for all that it was not possible for any planet to get closer to the sun than Mercury.