In
architecture, apsis is a synonym for
apse.Aphelia redirects here. For the
moth genus, see Aphelia (moth).Apogee redirects here. For the
video game publishing and developing company, see
Apogee Software. For the
album by
Bongzilla, see
Apogee (album). In
astronomy, an apsis, plural apsides (
IPA: //) is the point of greatest or least distance of the
elliptical orbit of an
astronomical object from its center of attraction, which is generally the
center of mass of the system. The point of closest approach is called the periapsis or pericentre and the point of farthest excursion is called the apoapsis (Greek από, from, which becomes απ before a vowel, and αφ before rough breathing), apocentre or apapsis (the latter term, although etymologically more correct, is much less used). A straight line drawn through the periapsis and apoapsis is the line of apsides. This is the major axis of the
ellipse, the line through the longest part of the ellipse.
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