While we know how the science turned out, people like Bellarmine and the majority of astronomers did not have the benefit of our hindsight. At the time the question was far from settled and there were actually no less than seven competing models under debate, of which the Copernican model was very much the unfavoured outsider. They consisted of:So the issue was not just heliocentrism v geocentrism, or whether the Earth moves. There were a bunch of possibilities, and it was not clear how to physically distinguish them.
(Thanks to Michael Flynn for this neat summary)
- Heraclidean. Geo-heliocentric. Mercury and Venus circle the Sun; everything else circles the Earth.
- Ptolemaic. Geocentric, stationary Earth.
- Copernican. Heliocentric, pure circles with lots of epicycles.
- Gilbertian. Geocentric, rotating Earth.
- Tychonic. Geo-heliocentric. Sun and Moon circle the Earth; everything else circles the Sun.
- Ursine. Tychonic, with rotating Earth.
- Keplerian. Heliocentric, with elliptical orbits.
He says "we know how the science turned out", as if everyone knows that Kepler turned out to be right. Kepler's model did give the best results for a century or so. Then can Newtonian models with planets like Jupiter pulling other planets out of their elliptical orbits. For the last century, the consensus has been general relativity, where motion is relative and you can think of the Earth as stationary or as moving however you please, as long as the coordinate transformations are done properly in the covariant equations.