Perihelion and Aphelion
Perihelion and Aphelion, The perihelion is the point on the orbit of a planet or comet that is closest to the sun. The point on the orbit farthest from the sun is the aphelion. The speed of a body in the solar system is greatest at the perihelion and least at the aphelion. For satellites of the earth, the corresponding terms are perigee and apogee; for an object in orbit around the moon, perilune and apolune are used.