# What is a deferent in astronomy?

## What is a deferent in astronomy?

Astronomy. (in the Ptolemaic system) the circle around the earth in which a celestial body or the center of the epicycle of its orbit was thought to move.

Is a deferent an orbit?

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 a deferent Ptolemy?

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.

Does the moon have an epicycle?

The overall orbit of the center of the moon’s epicycle is roughly the inner ovoid curve. If the proper Ptolemaic radial dimensions could be shown, it would be seen that this orbit is very nearly an ellipse.

## What is an epicycle supposed to explain?

In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (from Ancient Greek: ἐπίκυκλος, literally upon the circle, meaning circle moving on another circle) was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets.

Do epicycles exist?

Epicycles worked very well and were highly accurate, because, as Fourier analysis later showed, any smooth curve can be approximated to arbitrary accuracy with a sufficient number of epicycles.

### Do epicycles actually happen?

Who proposed epicycles?

Apollonius of Perga
It was first proposed by Apollonius of Perga at the end of the 3rd century BC. It was developed by Apollonius of Perga and Hipparchus of Rhodes, who used it extensively, during the 2nd century BC, then formalized and extensively used by Ptolemy of Thebaid in his 2nd century AD astronomical treatise the Almagest.

## What’s the difference between an epicycle and a deferent circle?

(mathematics) Any circle whose circumference rolls around that of another circle, thus creating a hypocycloid or epicycloid. Showing deference. (obsolete) Serving to carry; bearing. Bodies deferent . (obsolete) That which carries or conveys. Though air be the most favorable deferent of sounds.

Why did Ptolemy invent the deferent and epicycle?

Deferents and epicycles in the ancient models did not represent orbits in the modern sense. Claudius Ptolemy refined the deferent/epicycle concept and introduced the equant as a mechanism for accounting for velocity variations in the motions of the planets.

### What did the deferent and epicycle tell us about the planets?

In particular it explained the apparent retrograde motion of the five planets known at the time. Secondarily, it also explained changes in the apparent distances of the planets from the Earth.

How did Copernicus use the deferent and epicycle model?

In keeping with past practice, Copernicus used the deferent/epicycle model in his theory but his epicycles were small and were called “epicyclets”. In the Ptolemaic system the models for each of the planets were different and so it was with Copernicus’ initial models.