[baryphonic]

Galileo also couldn't explain the lack of an observed parallax effect between opposite seasons given the ideas about optics at the time.

When Kepler's model arrived, it was so much better at predicting the positions of all planets except Mercury than any previous model that it was clearly superior. Galileo's was bad at predicting and just contradicted the accepted observations of the day.

IMO Galileo should be better remembered for objects of different masses falling at the same rate and the original idea that all motion is relative (when observing from an internal frame).

[jcranmer]

> Galileo also couldn't explain the lack of an observed parallax effect between opposite seasons given the ideas about optics at the time.

That's not entirely correct. The lack of parallax was explained by the stars being far away; the problem with that explanation is that Brahe had measured the apparent stellar diameter of stars, which implied that for the stars to be as big as they appear to be to us, they would have to be far, far larger... which violates the underlying Copernican principle that the sun is but a normal star.

[graemep]

The Copernican model was heliocentric, surely? It placed the sun motionless at the centre of the universe. That makes the sun anything but a normal star.