Ptolemy had no problems with the basic concepts of Aristotle's design. he thought it was ingenious. the problem he did have was with the figures. they just didn't add up as closely as he thought they should and he set out to perfect Aristotle's model to the point where the numbers matched up. He made three distinct changes to Aristotle's model. When all of these changes were put together his numbers were far closer to the data collected by observation than Aristotle's ever were.
The first change Ptolemy made was that the Earth was placed on the center of all the spheres. Instead Ptolemy's model placed the Earth a little off center. The spheres would then rotate a little bit around the Earth in a very small circle. The reason the Earth was at the center of everything though was because of religious practices but because Ptolemy moved the earth so slightly it wasn't seen as that big of a problem.
The second change Ptolemy made to Aristotle's model was that he added more epicycles. Ptolemy put epicycles on epicycles for some planets and adjusted their velocities to better explain their motion.
The third and final change that Ptolemy made to Aristotle's model was that he placed the epicycles off center too. Ptolemy placed the center of the epicycles a little off of the deferent so that there would be another weird rotation that account for making the numbers look better.
All in all Ptolemy's model fixed the problem with the numbers of Aristotle's model but complicated it a little bit. None the less, it was the model used for over 1600 years until Copernicus came up with his heliocentric theory...
