Heliocentric View (Reality)
Geocentric View (Apparent)
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Explanation
Planetary retrograde is an apparent phenomenon where an outer planet (like Mars) appears to move backward in the sky when Earth (inner planet) overtakes it in its orbit.
The heliocentric view shows the true solar system structure: the Sun at center, Earth orbiting with a 1-year period, Mars orbiting with about 1.88-year period. When Earth overtakes Mars, the line of sight changes dramatically.
The geocentric view shows the apparent motion from Earth: Mars traces a distinctive zigzag or loop pattern across the sky. During retrograde (highlighted in red), Mars appears to move westward, opposite to its usual eastward motion.
This phenomenon puzzled ancient astronomers for thousands of years until Copernicus proposed the heliocentric model. In the heliocentric view, retrograde is simply a natural result of relative motion.