The orbits and positions of the planets or "wanderers" could not be accurately accounted for before the invention of the telescope although star positions were known.

Understanding came with the revolutionary work of Galileo, Brahe, and Kepler which, together with Newton's contributions, finally swept away the Greek concept of an earth-centered universe and established the present model of the solar system.

The Greeks had simplified celestial mechanics according to the simple doctrine that "matter behaves according to nature."