# What does epicycle explain?

## What does epicycle 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.

## Who used epicycles to explain?

Claudius Ptolemy
The most important solution to this problem was proposed by Claudius Ptolemy in the 3rd century AD. He argued that planets move on two sets of circles, a deferent and an epicycle. This explained retrograde motion while keeping the planets in their circular orbits around the Earth.

How is an epicycle different from a different?

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).

Who introduced the concept of epicycles?

Ptolemy believed that the heavenly bodies’ circular motions were caused by their being attached to unseen revolving solid spheres. For example, an epicycle would be the “equator” of a spinning sphere lodged in the space between two spherical shells surrounding Earth.

### Who proposed epicycles?

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). Because one half of an epicycle runs counter to the general motion of the deferent path, the…

### How do epicycles explain retrograde motion?

Epicycles Explain Retrograde Motion. 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.

Why did Ptolemy proposed the idea of epicycles?

In order to preserve the geocentric cosmology of the time and to account for retrograde motion of Mars, Ptolemy had to make a model of planetary motion that invoked the use of epicycles. An epicycle is basically a little “wheel” that orbits on a bigger wheel.

What is the problem with epicycles?

The problem is that the epicycle containing Mercury, the epicycle containing Venus, and the Sun all orbited around the Earth in one year! So their order was reluctantly agreed upon because Mercury moved fastest on it epicycle, Venus next fastest, and of course the Sun had no epicycle (because it never retrograded).

#### Who introduced 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.

#### Does each planet spin in an epicycle?

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). Because one half of an epicycle runs counter to the general motion of the deferent path, the…

What caused epicycles?

Do planets move in epicycles?

As the center of the epicycle moves around the deferent at constant angular velocity, the planet moves around the epicycle, also at constant angular velocity.

## What planets have epicycles?

Who is Ptolemy for kids?

–170?). Ptolemy was an influential astronomer, geographer, and mathematician of the ancient world. His theories about the universe dominated scientific thought until the Middle Ages. Almost nothing is known about Ptolemy’s life.

What are epicycles quizlet?

Epicycle. The small circle followed by a planet in the Ptolemaic theory. The center of this follows a larger circle (the deferent) around Earth. Deferent.

### What did Ptolemy discover for kids?

Most significantly, Ptolemy proposed that the Earth was at the center of the universe. In his model of the solar system, the sun, moon, and planets revolved around the Earth. Scholars believed this theory until it was replaced by Copernicus’ system in the 16th century.

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