How did copernicus discover heliocentrism?
Retrograde motion of the other planets only makes sense when using a sun centered solar system. He worked out an accurate model for explaining this. That is the reason he gets credit. However, Copernicus wasn’t the first to “discover” the solar system to be heliocentric. It can be traced back as far as 4th century BC to Aristarchus Plus at least a half dozen others throughout history across the far east, middle east, India, Greece and even Europe. So to answer your question, How did he discover it? He really didn’t. The concept was old and even accepted by some (not the church). He took information that was already available and created a model to explain the science.
