Ptolemy was approximating Kepler’s law, without knowing it. The reasons are: the elliptical orbits of the planet are close to a circle; the eccentric takes the role of a focus, approximating Kepler’s first law; Ptolemy’s equant has the effect of approximating Kepler’s second law. Ptolemy’s major contribution, however, was that his model could so accurately explain the motions of heavenly bodies, it became the model for understanding the structure of the solar system.