In Ptolemy's theory, retrograde planetary motion is explained as

A) the backward part of the planet's loop-the-loop orbits around Earth.
B) due to the back-and-forth or "oscillatory" motion that planets make as they move along their circular orbits around Earth.
C) due to the natural wandering of the celestial sphere of background stars.
D) a result of Earth's motion: as Earth passes another planet, that planet appears to move backward as seen against the background stars.
E) Actually he didn't have an explanation for this.


A

Physics & Space Science

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