born in modern Turkey. He showed that the ellipse, parabola, and hyperbola are all curves formed by a plane intersecting a cone in different ways, i.e. that they are conic sections. The orbital path of an unperturbed body moving in a gravitational field follows one of these three curves, as would come to be appreciated by later astronomers such as E. Halley, who translated Apollonius’ book Conics. Apollonius also originated the mathematical concept of motion based on epicycles and deferents, later taken up by Hipparchus and Ptolemy to explain planetary motion.