Apsis
extreme point in an object's orbit
An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault' (third declension); pl. apsides AP-sih-deez) is one of the two extreme points in the orbit of a planetary body about its primary body, either the farthest point (apoapsis) or the nearest point (periapsis). The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two apsides.
Apsides pertaining to orbits around different bodies have distinct names to differentiate themselves from other apsides. Apsides pertaining to geocentric orbits, orbits around the Earth, are at the farthest point called the apogee, and at the nearest point the perigee, as with orbits of satellites and the Moon around Earth. Apsides pertaining to orbits around the Sun are named aphelion for the farthest and perihelion for the nearest point in a heliocentric orbit. 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.
General description
There are two apsides in any elliptic orbit. The name for each apsis is created from the prefixes ap-, apo- (from ἀπ(ό), (ap(o)-) 'away from') for the farthest or peri- (from περί (peri-) 'near') for the closest point to the primary body, with a suffix that describes the primary body. The suffix for Earth is -gee, so the apsides' names are apogee and perigee.
Begin with the source’s own compact description: “Apsis” is extreme point in an object's orbit. The dossier treats that line as a proposition to test through Apsis, extreme and point, not as a finished interpretation.
Why this record matters
The phrase “extreme point in an object's orbit” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 21, 2026. The linked authority identifier is Q83481. None of the 0 selected statements returned an explicit reference.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Apsis” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.