What I'd like to see is a model where you could lift up the sun off its post, turn the whole thing upside down, put the earth down on the same post, and crank out "Ptolomeic" mathematical orbits.) There is apparently a Ptolemaic orrery at the Birmingham Museum of Science, so... if you are ever in the UK. p ------------------------------------------------------------------ To change your Lit-Ideas settings (subscribe/unsub, vacation on/off, digest on/off), visit www.andreas.com/faq-lit-ideas.html