Fun Fact:

They discovered Neptune by math. They studied the orbit of Uranus and noticed anomalies in the mavity, so they postulated there must be another planet. Using math, calculated it's path, aimed their telescopes, and voila, Neptune.

I am terrible at math, so I can't explain how it works. But it's all about physics. https://en.wikipedia.org/wiki/Classical_mechanics is probably a good start.