Respuesta :

Answer:

The heliocentric model explains retrograde motion because Mars only appears to move backward as Earth passes it in its orbit around the Sun. ... To explain the retrograde motion of planets, it was suggested that the Earth and planets orbit around the Sun (heliocentric, or Sun-centered model).

Explanation:

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Apparent retrograde motion
The word planet comes from the Greek 'planete' which means 'wandering', this because they were the only ones with the properties of modifying their position with respect to the fixed stars in the deep sky. For the Greeks, the sun, the moon, Mercury, Venus, Tuesday, Jupiter and Saturn were considered planets.

Answer and Explanation:
It occurred when the planet that was observed retreated in its orbit around the sun, it was giving an apparent image that once the body advanced in its orbit, it began to retreat and again to advance. At that time, there was no knowledge of the heliocentric system and that what was observed as a retrogression was a projection on the celestial plane of the planet, circling the sun.

http://www.astronomy.ohio-state.edu/~depoy/Astro161/Notes/class5.pdf