The two points in an elliptical orbit that lie closest to or farthest from the centre of the body being orbited; sing. apsis or apse. The closest point is the periapsis (or periapse) and the farthest point the apoapsis (or apoapse). The straight line joining these two points is the line of apsides, and is the same as the major axis of the orbit. In the case of the Earth’s orbit around the Sun, the apsides are perihelion and aphelion.