KEPLER
All the models explain retrograde motion because it is such an obvious phenomenon. In Copernicus's model an outer planet goes into retrograde motion when the inner planet overtakes it so that it appears from the inner planet to be going backwards along the ecliptic.
The observed retrograde motion of planets led Ptolemy to add epicycles to Aristotle's system. Epicycles were small circles that planets moved in on their larger circular orbits around Earth in order to explain the appearances of retrograde motion.
Mercury and Venus are the two planets that retrograde motion around the sun.
Epicycles and deferents were used in early models of the universe to accurately predict the positions of planets in the sky without fully understanding the heliocentric model. They were an attempt to explain the apparent retrograde motion of planets without the advanced knowledge of elliptical orbits.
Actually, 3 planets rotate in a retrograde motion, which, by the way, means that they rotate East to West, or in a counterclockwise motion. Most planets rotate in a clockwise direction, or West to East. The three planets that rotate in a retrograde motion are Venus, Uranus and Pluto.venus
Venus and Uranus have retrograde rotation.There are other meanings of retrograde motion, but retrograde rotation fits the question best.
to explain the motion of planets, especially the phenomenon of retrograde motion where planets appear to temporarily reverse their direction of motion. Ref: Andrew Liddle "An Introduction to modern Cosmology".
Retrograde motion important in astronomy because it helped to explain that the planets revolved around the Sun. Retrograde motion is the ability of some objects to rotate in a direction that is opposite what is expected.
If, as ancient astronomers thought, that our Earth was the center point of rotation for other planets, then it is difficult to explain why those planets would move in a direction opposite to their rotation. Ptolemy came up with a solution that worked, but it was a cumbersome one. Nicolae Copernicus was able to show that this retrograde motion could be explained easily if it were assumed that our Sun was the actual center of rotation of the planets.
The "apparent" reverse or backwards motion of a planet as observed from Earth. The innermost planets appear to have a retrograde motion when viewed from Earth.
All planets orbit the sun in the direction that the sun is rotating. There are actually two planets that rotate by retrograde motion and are exceptions to this rule. These planets are Venus and Uranus.
Uranus and Venus are the two planets in our solar system that have a retrograde rotation. All of the planets orbit the Sun.