Nicolaus Copernicus was a mathematician and astronomer who argued that the Sun rather than the Earth was the center of the universe.
Copernicus studied Ptolemy (#374 in our OLD DEAD WHITE GUYS series), the Alexandrine astronomer who developed the idea that Earth is the center of the universe and all the planets and stars revolve around her. Interesting side note: Copernicus learned Greek so he could read Ptolemy’s writings.
Ptolemy’s geocentric model doesn’t work in real life. To account for planets’ orbits that aren’t centered around Earth, you have to imagine an invisible center of gravity other than Earth’s. That is—if you watch them closely, the planets revolve around something else. In ad 1510 Copernicus figured that the planets—including Earth—are heliocentric. They revolve around the Sun.
That’s how the Solar System works, of course. Copernicus was right. This new way of thinking was a big deal in the world of science.