What aspect of Ptolemy's model would account for the changes in a planet's brightness as it undergoes retrograde motion?
A) the equant
B) motion along multiple epicycles
C) the velocity of an epicycle
D) the radius of an epicycle

Question

Quizplus · Accepted Answer

The radius of an epicycle in Ptolemy's model affects the distance between Earth and the planet, which in turn influences the planet's apparent brightness as it undergoes retrograde motion.

What Aspect of Ptolemy's Model Would Account for the Changes