Copernicus wasn't much of a scientist compared to some of the names on this list, because essentially all he did was propose a theory. He didn't have much evidence to back it up - any more than Aristarchus had. Kepler and Galileo were the ones who took the theory and showed it to be true, and also refined it (Kepler realised that everything happens in ellipses, which in a way was more important than putting the sun at the centre - it paved the way for Newton's explanation of how gravity and the inverse square law explain it all).