Deferent
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DEFERENT (Lat. deferens, bearing down), in ancient astronomy, the mean orbit of a planet, which carried the epicycle in which the planet revolved.
Deferent and epicycle
The basic elements of Ptolemaic astronomy, showing a planet on an epicycle (A) with a deferent (C) and an equant (B).
deferent A construct of the geocentric model of the solar system which was needed to explain observed planetary motions. A deferent is a large circle encircling the Earth, on which an epicycle moves.
degree See arc degree.
Deferent
The larger circle of which an epicycle revolves (the earth in this case).
Degenerate Matter ...
deferent: In the Ptolemaic theory, the large circle around Earth along which the center of the epicycle moved.
Deferent - One of the circles on which a planet moved according to the Ptolemaic model of the solar system ...
DEFERENT
The deferent is the large circular orbit around which a planet was thought to orbit, in one or many . Epicycles are circular orbits within orbits that were used to (incorrectly) describe the orbits of objects in the (about 150 A.D.).
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95. Deferent
The larger circle of which an epicycle revolves (the earth in this case).
The epicycle and deferent are a way to explain the retrograde motions of the outer planets. The deferent is the large circle that is also eccentric (Earth not in the middle), and upon this large circle, the epicycle is locatd.
Anomalies in a planet's motion were accounted for by the use of the epicycle, a circle centered on the circumference of a larger circle called the deferent.
Moreover, the system of movable eccentrics, and that of epicycles and deferents, accounted well for most of the irregularities observed in the motions of the Sun, the Moon, and the planets.
The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions.
Apollonius of Perga (c. 262 BC-c. 190 BCE) responded by introducing two new mechanisms that allowed a planet to vary its distance and speed: the eccentric deferent and the deferent and epicycle.
He found that these variations could be reproduced most conveniently by displacing the earth from the center of the deferent to a point called the eccentric.
In actual models, the center of the epicycle moved with uniform circular motion, not around the center of the deferent, but around a point that was displaced by some distance from the center of the deferent.
In Ptolemy's model, each planet is moved by two or more spheres (or strictly speaking, by thick equatorial slices of spheres): one sphere is the deferent, with a center offset somewhat from the Earth; ...
These circles upon circles were called "epicycles," and the larger circles were called "deferents." This is shown in the image to the right. This is a "three planet" system, with the Earth at the center, and two planets around it.
As a planet moves around on its epicycle, the center of the epicycle (called the ``deferent'') moves around the Earth. When its motion brings it inside the deferent circle, the planet undergoes retrograde motion.
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.
The center of the epicycle always moves West to East (counterclockwise on the picture) along a big circle known as the deferent, and the planet always moves counterclockwise on the epicycle, ...
recalled Pocahontas in London, saying that she impressed those she met because she "carried her selfe as the daughter of a king" and when he met her in London, Smith referred to her deferentially as a "Kings daughter".
 See also: Epicycle, Earth, Planet, Sun, Astronomy
  
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