Ancient astronmers used shell theory. The earth was center, then came the moon, planets and sun, then other stars. At first it was a circular system. It seemed more "perfect", that degenerated into ellipses as the mathematics didn't work out.
Ptolemy proposed the use of epicycles (small circles) within deferents (larger circles) to explain the observed retrograde motion of planets. The epicycles were used to account for the variability in a planet's speed as it moved along the deferent in his geocentric model.
Both Copernicus' and Ptolemy's models aimed to explain the motion of celestial bodies in the sky. However, Copernicus placed the Sun at the center of the universe, while Ptolemy's model had Earth at the center. Both models used the concept of epicycles to explain the retrograde motion of planets.
Earths faster motion makes Mars appear to be going backwards, the backwards motion, in fact, is what caused retrograde motion. --Ptloemy used Epicycles to explain how geocentrical models worked.
Ptolemy is trying to explain in his model that each circle represents 1 planet's rotation and it's a scale drawing of the distance apart from each one!
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.
Ptolemy proposed the use of epicycles (small circles) within deferents (larger circles) to explain the observed retrograde motion of planets. The epicycles were used to account for the variability in a planet's speed as it moved along the deferent in his geocentric model.
Both Copernicus' and Ptolemy's models aimed to explain the motion of celestial bodies in the sky. However, Copernicus placed the Sun at the center of the universe, while Ptolemy's model had Earth at the center. Both models used the concept of epicycles to explain the retrograde motion of planets.
Earths faster motion makes Mars appear to be going backwards, the backwards motion, in fact, is what caused retrograde motion. --Ptloemy used Epicycles to explain how geocentrical models worked.
Earths faster motion makes Mars appear to be going backwards, the backwards motion, in fact, is what caused retrograde motion. --Ptloemy used Epicycles to explain how geocentrical models worked.
Ptolemy is trying to explain in his model that each circle represents 1 planet's rotation and it's a scale drawing of the distance apart from each one!
Ptolemy is trying to explain in his model that each circle represents 1 planet's rotation and it's a scale drawing of the distance apart from each one!
Ptolemy is trying to explain in his model that each circle represents 1 planet's rotation and it's a scale drawing of the distance apart from each one!
Ptolemy explained retrograde motion through his geocentric model of the universe, where Earth is at the center and all celestial bodies, including planets, orbit around it. He introduced the concept of epicycles, which are small circular orbits that planets follow while moving along a larger circular path called a deferent. When a planet moves along its epicycle in such a way that it appears to move backwards relative to the stars, it creates the observed retrograde motion. This model allowed Ptolemy to account for the complex movements of planets as observed from Earth.
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".
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.
Copernicus proposed a heliocentric model, where planets revolve around the sun, while Ptolemy's geocentric model placed Earth at the center of the universe with planets orbiting around it. Copernicus' model helped to explain retrograde motion more simply than Ptolemy's epicycles.
Ptolemy did not explain Venus phases in his geocentric model because he believed that Venus, like all other planets, moved around the Earth in perfect circles and did not exhibit phases like the Moon. His model could not account for the varying phases of Venus because it was based on circular motion and did not include elliptical orbits or the correct understanding of planetary motion.