Complex sentence: Astronomers such as Eudoxus (contemporary with Plato) observed planetary motions and cycles, and created a geocentric cosmological model that would be accepted by Aristotle--this model generally lasted until Ptolemy, who added epicycles to explain the retrograde motion of Mars.
Split into simpler sentences: Astronomers such as Eudoxus (contemporary with Plato) observed planetary motions and cycles, and created a geocentric cosmological model that would be accepted by Aristotle. This model generally lasted until Ptolemy, who added epicycles to explain the retrograde motion of Mars.