In orbital mechanics, an apsis is either of the two extreme points in an elliptical orbit around a central body: periapsis, the closest approach, and apoapsis, the farthest point. For orbits around Earth these are called perigee and apogee, around the Sun perihelion and aphelion, with equivalent terms used for other bodies. The line connecting the two apsides, called the line of apsides, passes through the orbit's center and both foci.
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