Apollonius of Perga (; ; c. 262 BC – c. 190 BC) was a Greek geometer and astronomer noted for his writings on conic sections. His innovative methodology and terminology, especially in the field of conics, influenced many later scholars including Ptolemy, Francesco Maurolico, Johannes Kepler, Isaac Newton, and René Descartes. Apollonius gave the ellipse, the parabola, and the hyperbola their modern names. The hypothesis of eccentric orbits, or equivalently, deferent and epicycles, to explain the apparent motion of the planets and the varying speed of the Moon, is also attributed to him. Ptolemy describes Apollonius' theorem in the Almagest XII.1. Apollonius also researched the lunar history, for which he is said to have been called Epsilon (e). The crater Apollonius on the Moon is named in his honor.