How did the Ptolemaic model explain retrograde motion of the planets?

And what exactly is retrograde motion? Please explain in non-complicated English, my astronomy book is confusing =/How did the Ptolemaic model explain retrograde motion of the planets?When we observe the other planets from Earth, as we watch them throughout the year - or longer - they sometimes appear to move backwards in the sky instead of their normal forwards motion. During this time, the planet in question is said to be in retrograde.



Ptolemy held the Earth as the center of our Solar System. To correct for seeing planets in retrograde, he came up with the idea of epicycles. Planets which not only travel around in a circle about Earth, but in a circle around the circle. This can be seen in this diagram.



http://www.polaris.iastate.edu/EveningSt鈥?/a>



We must note that the use of epicycles did not solve Ptolemy's problem as the predicted motion of the planets into future dates failed to place the planet where it was actually seen.