Complex sentence: In doing so, Copernicus moved heliocentrism from philosophical speculation to predictive geometrical astronomy--in reality it did not predict the planets' positions any better than the Ptolemaic system.
Split into simpler sentences: In doing so, Copernicus moved heliocentrism from philosophical speculation to predictive geometrical astronomy. In reality, Copernicus's system did not predict the planets' positions any better than the Ptolemaic system.