Chapter 3

An animation of page 131, the equivalence of a concentric-with-epicycle (left) with an eccentric (right), and the difference encountered with the use of the apparent instead of the mean sun:

On the left, the planet (blue or red) can be said to move around the black center, but with an epicycle. On the right, rather than offsetting the planet, we instead move the observer, making it an eccentric.