Question

Which idea did Ptolemy’s model use to explain why the planets appeared to move backward as they moved in their orbits?

Answer 1

Answer:

Ptolemy included epicycles in his orbits.

Explanation:

Ptolomy's model of the solar system was geocentric, where the sun, moon, planets, and stars all orbit the earth in perfectly circular orbits. The problem with perfectly circular orbit around the Earth is that they do not explain the occasional backward motion, or retrograde motion, of the planets.

The Greeks insisted that the motion of the planets be perfectly circular. Ptolemy modeled the planets making small circles around a point that orbited the Earth. These smaller circles were called epicycles, and they allowed the planets to move backward relative to the background stars.