The heliocentric model explains that the Earth and other planets go around the Sun, meaning at certain times, the Earth is closer or farther away from each planet. This accounts for the apparent planetary retrograde motion and brightness variations.
The word "Helios" in Greek means "sun." Heliocentric means that the sun is at the center. A heliocentric system is one in which the planets revolve around a fixed sun. Thus all the planets all revolve around the sun.
The explanation for retrograde motion in a heliocentric model is that retrograde occurs roughly when a faster moving planet catches up to and passes a slower moving planet.
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