Astronomical Revisionism

In the course of arguing for school vouchers, Andrew Coulson tries out a little analogy:

Unaware that the planets orbit the sun, pre-Copernican astronomers tried to reproduce their trajectories with clever, intricate, but inevitably doomed geocentric models. In a similar vein, the Center struggled unsuccessfully to reproduce market incentives within their state-centric policy environment.

This is neither here nor there as far as education policy goes, but people are under some serious misapprehensions regarding Copernicus. The thing about pre-Copernican astronomy was that it was actually very good at calculating the orbits of the planets. It was also nicely integrated into a theory of gravity -- objects fall toward the center of the earth because solids have a natural tendency to direct themselves toward the center of the universe. Copernicus, by boldly casting aside the geocentric theory, managed to wreck this theory of motion (he had nothing with which to replace it), and was able to replace the previous astronomical tables with new, less accurate ones. Copernicus, you see, assumed that the planets moved around the suns in circles, which gives you the wrong results. Pre-Copernican astronomers, by contrast, were able to use epicycles to very closely match the theory with the observed data.

The virtue of Copernicus' system is that it was much simpler to do Coperican calculations than it was to factor all the epicycles in. People liked it because it was only somewhat less accurate than its predecessor but substantially easier to use. It took decades, however, for later theorists to work out elliptical orbits and the modern theory of gravity that gave "Copernican" astronomy the theoretical foundations and accurate results that it initially lacked.