Hi all, the Ptolemaic geocentric system was accepted for ~2000 years before Galilei discovered (by telescope) that Venus goes around the Sun, not the Earth. However, AFAIK the Ptolemaic system reproduced the observations quite well (to a precision of 10' or so). Let's not talk here about crystalline spheres and such. Let's just talk about the mathematical content. AFAIK, it can be shown that the Ptolemaic system (with epicycles) is roughly equivalent to the Keplerian system (if you use enough epicycles, neglect planet's brightnesses and any telescopic evidence, and, most important, use the right parameters). After all, astrology has been done all thru the ancient times & middle ages, and astrological predictions (ephemerides) were correct to a certain degree, weren't they? My question: Where can I find a mathematical representation of the Ptolemaic system, especially the exact values of all parameters used? Is there any tables/software/applets on the web, especially to show where it agrees/disagrees with the modern system? Any help will be greatly appreciated.