Additional Notes & Thoughts
⇒ Epicycle (literally, “upon the circle”) is a geometric term for a small circle whose center moves around the circumference of a larger one.
⇒ Historically, the term was used to describe planetary orbits within the Ptolemaic system. In that system, the term was defined as “a circle in which a planet moves and which has a center that is itself carried at the same time on the circumference of a larger circle.” This was used to explain/account for the observed periodic irregularities in planetary motions.
⇒ The concept of the epicycle was used within the punctum aequans (or equant) developed by Ptolemy in the 2nd century AD to allow for the accounting of observable movement of the planets. This was done in order to maintain the long-standing theory of Aristotle concerning celestial bodies being in constant circular motion, while taking into account the observed movements of the bodies. Using the equant, Ptolemy was able to defend the theory of uniform circular motion by showing that the path of each planet was uniform around one point, while being circular around another point.