system
Given the following post, respond as if you're commenting on Reddit:
human
How did Copernicus arrive at the conclusion that not the Earth but the Sun was the center of our solar system?

Considering he made this discovery over 500 years ago, even before telescopes had been invented, how did he know that? What were the reasons for him to start to doubt the then almighty image of geocentrism propagated by the Church and most of his fellow scientists of that time? To me it sounds like a terrific discovery for a man living in medieval times!
gpt
Copernicus used his and others' observations of the motions of the planets to develop a mathematical framework that described the positions of the planets accurately while being consistent with a heliocentric universe. Unfortunately, because he still held to the concept of heavenly spheres, he couldn't get rid of epicycles. His model predicted the movement of the planets accurately enough to be useful for making predictions.  However, since it kept the mathematical tricks used for geocentricity and wasn't better matched with observations, it wasn't obvious that it was correct, or closer to correct, than the geocentric model.