Urbain Le Verrier's Unseen Planets

Sir Isaac Newton's laws of gravity had profound meaning for astronomers, because the mass of the planets around us, their distance, and their orbits followed these laws and made sense of what they observed. But at the time, there were only six known planets besides earth, from Mercury to Uranus. Most of them followed Newton's laws to a T., as calculated by astronomer Alexis Bouvard in 1821. But then there was Uranus, which progressed more slowly than Newton's laws would predict. Were those laws of gravitation flawed? Or was there something different about Uranus? An assistant astronomer at the Paris Observatory, Urbain Le Verrier, recorded variations in the orbits of both Uranus and Mercury. Le Verrier figured there might be another planet on the other side of Uranus, which would explain those variations. Using his hypothesis and the Uranus's orbit to chart the position of the unseen planet, Le Verrier knew where it should be, but couldn't get permission to use Paris's biggest telescopes to take a look. A colleague he knew in Berlin had access to an observatory, though, and that's how Neptune was discovered.

Le Verrier was rightfully honored for his discovery of Neptune, the first planet to be tracked by indirect information before it was observed. So then he turned his attention to the variations in Mercury's orbit and the idea that there could be another planet beyond Mercury even closer to the sun. When amateur astronomer Dr. Edmond Lescarbault observed a disc racing across the surface of the sun, Le Verrier announced another discovery- the planet Vulcan.
Now, you probably only know the planet Vulcan from Star Trek, and not from your science classes. You know what happened to Neptune (it's still there), but what about Vulcan? Read that story at Damn Interesting.