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Epicycle
01
(astronomy) a secondary circular orbit embedded within a primary circular orbit
02
a small circle whose center moves around the circumference of a larger circle
Example
In his astronomical work the Almagest, Ptolemy used a system of deferents and epicycles to explain the observed motions of planets across the night sky.
Copernicus disagreed with the Ptolemaic model adding unnecessary epicycles, believing instead that planets revolve in simpler circular orbits around the Sun.
The concept of an epicycle allows for the modeling of complex periodic movements in geometry and astronomy.
An epicycle can be visualized by imagining a small wheel rolling around the edge of a larger wheel.
The motion of a point on an epicycle can be described mathematically by combining the rotations of the smaller circle and the larger circle.
