The Copernican System
Nicolas Copernicus
1473-1543  Poland
Ptolemaic system was looking shaky because better observations (Arab) showed it kept missing the planetary positions.
Copernicus recognized that a heliocentric explanation was much simpler (but he just thought of it as asthetically better). It didn’t actually predict the positions better.
The Church was invested in the Ptolemaic system (tradition), and Copernicus waited until his death to publish. Most didn’t believe him.