I've always thought of the various observations Galileo made more as
refutations of the geocentric model than as "proof" of the heliocentric
one. As most of you know, it is indeed possible to make a workable
geocentric model of the solar system. Every planetarium program does
this! Most (all?) of them "cheat" by first computing the positions in
a heliocentric model and then doing a coordinate transformation. But
*including that transformation* the result is a perfectly good
geocentric model. The real difference is that the heliocentric model
is a LOT simpler (especially when you try to include a deeper physical
explanation (gravity) in addition to simple description). Science
works by refuting wrong theories and then choosing the simplest of the
remaining alternatives not by "proving" that any of them are correct.
Galileo's observations made it very clear that the geocentric models
had to be tortured beyond the breaking point to remain consistent with
the facts (while the heliocentric theory suffered no such problems).
-- Bill Arnett bill@No-Spam http://nineplanets.org/ Emerald Hills CA USA 37 27 N 122 15 W