What is 'retrograde motion' of planets?

Explanation

(i) During the observation of motion of the planets it is in the night sky by naked eyes over a period of a few months, it can be seen that the planets move eastwards and reverse their motion for a while and return to eastward motion again. This is called "retrograde motion" of planets.
(ii) Ptolemy introduced the concept of "epicycle" in his geocentric model. To explain this retrograde motion, according to this theory, while the planet orbited the Earth, it also underwent another circular motion termed as "epicycle". A combination of epicycle and circular motion around the Earth gave rise to retrograde motion of the planets with respect to Earth.
(iii) But Ptolemy's model became more and more complex as every planet was found to undergo retrograde motion.
(iv) According to heliocentric model, the Sun is at the centre of the solar system and all planets orbited the Sun. The retrograde motion of planets with respect to Earth is due to the relative motion of the planet with respect to Earth. The retrograde motion from the heliocentric point of view.

The Earth orbits around the Sun faster than Mars. Due to the relative motion between Mars and Earth, Mars appears to move backwards from July to October. In the same way the retrograde motion of all other planet was explained successfully by the Copernicus model. The heliocentric model slowly replaced the geocentric model, because of its simplicity.