Although Copernicus was really interested in astronomy, he worked in the Catholic Church.
His theory was that the Earth rotates daily on its axis and orbits yearly around the sun. He also argued that the planets circled the Sun.
This challenged the long held view that the Earth was stationary at the centre of the universe with all the planets, the Moon and the Sun rotating around it.
Although his model wasn't completely correct, it formed a strong foundation for future scientists to build on and improve our understanding of the motion of planets.