# Apsis

## Either of two extreme points in a celestial object's orbit / From Wikipedia, the free encyclopedia

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An **apsis** (from Ancient Greek * *ἁψίς* ( hapsís)* 'arch, vault'; pl.

**apsides**/ˈæpsɪˌdiːz/

*AP-sih-deez*)[1][2] is the farthest or nearest point in the orbit of a planetary body about its primary body. The

**line of apsides**is the line connecting the two extreme values.

For example, for orbits about the Sun the apsides are called *aphelion* (farthest) and *perihelion* (nearest). The Moon's two apsides are the farthest point, *apogee*, and the nearest point, *perigee*, of its orbit around the host Earth. Earth's two apsides are the farthest point, *aphelion*, and the nearest point, *perihelion*, of its orbit around the host Sun. The terms *aphelion* and *perihelion* apply in the same way to the orbits of Jupiter and the other planets, the comets, and the asteroids of the Solar System.

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