Which concept was NOT a part of Kepler's Laws of Planetary Motion?

Question

Quizplus · Accepted Answer

Kepler's laws did not involve the concept of epicycles, which were used by earlier astronomers to explain the apparent retrograde motion of planets. Kepler's Laws of Planetary Motion do not involve epicycles. Epicycles were part of the geocentric model of the solar system developed by Ptolemy and other ancient astronomers. Kepler developed his laws by closely analyzing the observations made by Tycho Brahe, who had meticulously documented the positions of the planets over many years, and did not rely on the artificial construct of epicycles.

Which Concept Was NOT a Part of Kepler's Laws of Planetary