Is there a general term for epicycles, deferents, and eccentrics in Ptolemaic astronomy?

History

What is the epicycle and deferent and the eccentric model of planetary orbits?

In order to explain the motion of the planets, Ptolemy combined eccentricity with an epicyclic model. In the Ptolemaic system each planet revolves uniformly along a circular path (epicycle), the centre of which revolves around Earth along a larger circular path (deferent).

What are epicycles in the Ptolemaic system?

In the Ptolemaic model of the solar system, epicycles are small circular orbits that follow around much larger orbits around the Earth. These larger orbits of planets and the Sun around the Earth are called deferents. An epicycle is a circular path orbiting a particular point that follows the path of a deferent.
 

What is the meaning of eccentric and epicycles?

(An eccentric circle is a circle that is slightly off-centre from Earth, and an epicycle is a circle that is carried and rides around on another circle.)

What is an eccentric Ptolemy?

Ptolemy used three basic constructions, the eccentric, the epicycle, and the equant. An eccentric construction is one in which the Earth is placed outside the center of the geometrical construction. Here, the Earth, E, is displaced slightly from the center, C, of the path of the planet.

What is the difference between deferent and epicycle?

Once the epicycle is defined, the main circle that defines the planet’s orbit is known as the deferent. The planet moves in steady, circular motion around the epicycle while the center of the epicyle moves in steady, circular motion around the center of the deferent.

What is the difference deferent and epicycle?

Ptolemy explained the apparent “looping motion” of the planets by placing the center of one rotating circle, called the epicycle, which carried the planet, on another rotating circle, called the deferent, so that together the motions of the two circles produced the observed looping motion of the planet.

What are the two primary components of the Ptolemaic universe model?

In the Ptolemaic system, each planet is moved by two or more spheres: one sphere is its deferent which is centered on the Earth, and the other sphere is the epicycle which is embedded in the deferent. The planet is embedded in the epicycle sphere.

Who proposed Deferents and epicycles?

According to Copernicus, a heliocentric planetary orbit is a combination of two circular motions. The first is motion of the planet around a small circular epicycle, and the second is the motion of the center of the epicycle around the sun on a circular deferent. Both motions are uniform, and in the same direction.

What is meant by epicycle?

epi·​cy·​cle ˈe-pə-ˌsī-kəl. in Ptolemaic astronomy : a circle in which a planet moves and which has a center that is itself carried around at the same time on the circumference of a larger circle. : a process going on within a larger one. epicyclic.



What happened to epicycles and deferents in the model of planetary orbits?

The deferent rotates around the Earth while the epicycle rotates within the deferent, causing the planet to move closer to and farther from Earth at different points in its orbit, and even to slow down, stop, and move backward (in retrograde motion).

What is an epicycle?

epicycle (plural epicycles) (astronomy) A small circle whose centre is on the circumference of a larger circle; in Ptolemaic astronomy it was seen as the basis of revolution of the “seven planets”, given a fixed central Earth. quotations ▼

What is the deferent in the geocentric model?

In the Ptolemaic system, each planet is moved by a system of two spheres: one called its deferent; the other, its epicycle. The deferent is a circle whose center point, called the eccentric and marked in the diagram with an X, is distant from the Earth.

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