How did the ptolemaic model explain the apparent retrograde motion of the planets? a) this model claimed that the planets moved on small circles which, in turn, moved on larger circles around the earth. b) the motion on the small circles, called "epicycles", combined with the motion on the larger circle sometimes produced backward motion. in the ptolemaic model, retrograde motion occurred when the earth passed by another planet in its orbit of the sun. c) this model claimed that the planets resided on giant spheres that sometimes turned clockwise and sometimes turned counterclockwise. d) all of the above e) none of the above

Correct answer is Option D) All of the Above.

The Geocentric model It was developed by Claudio Ptolemy (2nd century AD), so it is also called "Ptolemaic System". He placed the Earth at the center of the universe; the Sun described a circular orbit around the Earth in a period of one day.

In the Ptolemaic system, each planet is moved by two or more spheres: one sphere is its deferential that centers on the Earth, and the other sphere is the epicycle that fits into the deferential. The planet fits into the sphere of the epicycle. The deferential rotates around the Earth while the epicycle rotates within the deferential, causing the planet to zoom in and out of the Earth at various points in its orbit, including causing it to slow down, stop, and move in the opposite direction (in retrograde motion).

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