The circle acted as a deferent, carrying an epicycle along which the Moon was assumed to move in a retrograde direction.
32.
He naturally regarded circular motion as fundamental and then used the circular motion of deferents and epicycles in his earth-centered theory.
33.
However, while providing for similar explanations, the later deferent and epicycle model was flexible enough to accommodate observations for many centuries.
34.
Astronomers often continued using the equants instead of the epicycles because the former was easier to calculate, and gave the same result.
35.
:Retrograde motion was long understood ( it is easily observable in Mars ) and was exactly the stimulus for epicycles, yes.
36.
From ancient times until the 16th and 17th centuries, the motions of the planets were believed to follow perfectly circular epicycle ).
37.
But to make his system fit the observations as well as Ptolemy's system, Copernicus had to introduce still more epicycles.
38.
Koestler, in his history of man's vision of the universe, equates the number of epicycles used by Copernicus at 48.
39.
Apollonius of Perga ( c . 262 c . 190 BC ) had introduced the deferent and epicycle and the eccentric deferent to astronomy.
40.
The germ of the idea is to be found in ancient writers who used sundials and Ptolemaic epicycles to illustrate the divine order of the world.
