A circle, whose center moves round in the circumference of a greater circle; or a small circle, whose center, being fixed in the deferent of a planet, is carried along with the deferent, and yet, by its own peculiar motion, carries the body of the planet fastened to it round its proper center.
A circle which rolls on the circumference of another circle, either externally or internally.
A construct of the geocentric model of the solar system which was necessary to explain observed planetary motions. Each planet rides on a small epicycle whose center in turn rides on a larger circle (the deferent).
a circle that rolls around (inside or outside) another circle; generates an epicycloid or hypocycloid
a circle upon which a planet moves and whose center is on another circle
a secondary circle with its center moving along the main circle
A secondary circle centered on another, usually larger, circle. It's center moves along the circumference of the main circle.
A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle (the deferent).
Epicycles are circular orbits within orbits that were used to (incorrectly) describe the orbits of objects in the Ptolemaic system (about A.D. 150). In Ptolemy's model of the solar system, an orbiting planet (or moon) moved in a series of circular orbits (epicycles) and the center of these epicycles orbited in another circular orbit (called the deferent) that was a circle offset from the Earth. Many layers of epicycles were needed to approximate real (elliptical) orbits with their retrograde motion. Copernicus also used epicycles in his heliocentric (sun-centered) solar system model (in the mid 1500's). Epicycles were used to predict orbits until Kepler discovered the elliptical nature of orbits (early in the 1600's).
An attempt to explain the retrograde loop in the earth centered universe, by attaching the planets to epicycles and having them revolve around that, and in turn around the earth.
a device in Ptolemy's Earth-centered model that makes a planet execute a small circular motion around a point that is itself in a circular orbit around the Earth. It was used to explain retrograde motion.
Small circles that the Sun, planets, and moon where thought to follow while they traveled in their much larger orbits around the fixed Earth.
Smaller circle in the Ptolemaic system along which the planet moves while the center of the circle revolves about its deferent.