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.
Facts
Concept Domain Formulated YearEnglish aphelion is attested from the 1650s, a Grecianized form of Kepler's Modern Latin aphelium; perihelion was coined the same way to name the near point. Proposed ByJohannes Kepler, who coined the terms perihelion and aphelion to describe orbital extremes around the Sun. 1 Connections
Associated With
Source Wikipedia (space and spaceflight articles)
Sources
1. Wikipedia (space and spaceflight articles)
Wikimedia FoundationWikipedia, Apsis, Etymology sectionQuote, Wikipedia, Apsis, Etymology section
The words perihelion and aphelion were coined by Johannes Kepler to describe the orbital motions of the planets around the Sun.
2. Etymonline (Online Etymology Dictionary)
Douglas HarperEtymonline, aphelion entry, Origin sectionQuote, Etymonline, aphelion entry, Origin section
Modern Latin aphelium (itself attested in English from 1650s), coined by Johannes Kepler based on Greek apo hēliou
Apsis (Wikipedia)
Lead section
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).
In Group: Orbital Elements and Celestial Mechanics, Lead sentence
An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault' (third declension); pl.
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