Why did Ptolemy have the planets orbiting Earth on "circles upon circles" in his model of the universe?
A) to explain why more distant planets take longer to make a circuit through the constellations of the zodiac
B) to explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky
C) to explain why the Greeks were unable to detect stellar parallax
D) To properly account for the varying distances of the planets from Earth
E) To explain why Venus goes through phases as seen from Earth

Question

Quizplus · Accepted Answer

Ptolemy used "circles upon circles" or epicycles in his geocentric model to explain the apparent retrograde motion of planets, where they appear to move westward against the background stars.

Why Did Ptolemy Have the Planets Orbiting Earth on "Circles