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

Question

Quizplus · Accepted Answer

Ptolemy's model had the planets orbiting Earth on "circles upon circles" in order to explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky. This is known as retrograde motion and was a major challenge for astronomers trying to understand Earth's place in the universe.

Why Did Ptolemy Have the Planets Orbiting Earth on "Circles