[[File:Apogee (PSF) mul.svg|lang=zxx|thumb|345px|The apsides refer to the farthest (2) and nearest (3) points reached by an orbiting [[planetary-mass object|planetary body]] (2 and 3) with respect to a [[primary (astronomy)body|primary, or host, body]] (1).]]
An '''apsis''' ({{etymology|grc|''{{wiktgrc|ἁψίς}}'' (hapsís{{grc-transl|ἁψίς}})|arch, vault}}; {{plural form|'''apsides'''}} {{IPAc-en|ˈ|æ|p|s|ɪ|ˌ|d|iː|z}} {{respell|AP|sih|deez}})<ref>{{cite Dictionary.com|apsis}}</ref><ref>{{cite American Heritage Dictionary|apsis}}</ref> is the farthest or nearest point in the [[orbit]] of a [[planetary-mass object|planetary body]] about its [[primary (astronomy)|primary body]]. The '''line of apsides''' is the line connecting the two [[maximum and minimum|extreme values]].
The '''line of apsides''' is the line connecting the two [[extreme value]]s.
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]]. The 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[[planet]]s, the comets[[comet]]s, and the asteroids[[asteroid]]s of the [[Solar System]].
