The Geocentric Model
Ancient Greek Philosophers such as Aristotle, Plato, and others, porposed the geocentric model of the universe, claiming that the Earth was the center of the universe and all the planets and the stars revolved around us in concentric circles. This theory was then ammended by Ptolemy to account for the changes in certain planet's luminosity. He determined that, rather than the planets and the sun simply be orbiting around the Earth, they would simultaneously be moved by a system of two spheres creating a second path of circular motion (shown in the below link). This explaination was widly accepted for over a thousand years, including the time da Vinci lived.