sentences:  In addition, Copernicus's theory provided a strikingly simple explanation for the apparent retrograde motions of the planets—namely as parallactic displacements resulting from the Earth's motion around the Sun—an important consideration in Johannes Kepler's conviction that the theory was substantially correct.In the heliocentric model the planets' apparent retrograde motions' occurring at opposition to the Sun are a natural consequence of their heliocentric orbits.In the geocentric model, however, these are explained by the ad hoc use of epicycles, whose revolutions are mysteriously tied to that of the Sun's.