Vulcan is many things, most famously a planet from Star Trek. While I admire many of the qualities of the fictional Vulcans, their story isn't the one I want to tell, their story isn't the real Vulcan. Let's take a trip.
Newton had done it. He blew the lid off of the galaxy. Gravity, calculus, classical mechanics; he did it, and he gave us the first gaze into the hidden clockwork of the universe. Before, we had but tiny peepholes with muddy lenses, but now humanity could look under the universe's skirt and stare.
Science leapt forward.
Mercury was a problem. We would look up at the bright shiny blobs within our solar system, crunch the numbers, and get a great prediction about when we would see our shiny blobs again. Newton's formulas worked tremendously well for all the planets, except Mercury. Obviously, Newton's Laws worked, they were not the flaw.
To account for Mercury's irregular orbit, some scientists posited the existence of another planet, one we had never seen before. The search was on for the planet Vulcan. Vulcan would have been small, near the sun, and in some sort of groovy gravitational rhythm with Mercury.
They couldn't find it.
Albert Einstein showed we were looking in the wrong place. One of his theory's first great tests was accurately predicting Mercury's orbit. With it, he showed a fundamental flaw in Newton's laws, laws that elsewhere are so accurate. Einstein's theory accounted for an error without upsetting observations of the other planets. With Relativity, one of our greatest scientists eradicated an entire planet, challenged the authority of Newton, and advanced our understanding of the universe.
Vulcan is so near to my heart because its story is the story of science. Predictions are made given our current understanding, when they are not met we must alter our predictions or alter our understanding. Relativity on its own is a masterpiece, it is transcendent because it dances so well with Newton.
But science never really gave up on Vulcan, we're still looking.