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The apsides refer to the farthest (2) and nearest (3) points reached by an orbiting planetary body (2 and 3) with respect to a primary, or host, body (1). An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault'; pl. apsides / ˈ æ p s ɪ ˌ d iː z / AP-sih-deez) [1] [2] is the farthest or nearest point in the orbit of a planetary body about its primary body.
apogee The point at which a body orbiting the Earth (such as the Moon or an artificial satellite) is furthest from the Earth. Contrast perigee. apparent magnitude. Also visual brightness (V). A measure of the brightness of a celestial body as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere. The ...
At perigee (closest), since the Moon is up to 14% closer to Earth than at apogee (most distant), it subtends a solid angle which is up to 30% larger. Consequently, given the same phase, the Moon's brightness also varies by up to 30% between apogee and perigee. [208] A full (or new) moon at such a position is called a supermoon. [202] [203] [209]
An event called a "supermoon" occurs when the full Moon is closest to Earth (perigee). The largest possible apparent diameter of the Moon is the same 12% larger (as perigee versus apogee distances) than the smallest; the apparent area is 25% more and so is the amount of light it reflects toward Earth.
If the argument of perigee is zero, meaning that perigee and apogee lie in the equatorial plane, then the ground track of the satellite will appear the same above and below the equator (i.e., it will exhibit 180° rotational symmetry about the orbital nodes.) If the argument of perigee is non-zero, however, the satellite will behave differently ...
r a is the radius at apoapsis (also "apofocus", "aphelion", "apogee"), i.e., the farthest distance of the orbit to the center of mass of the system, which is a focus of the ellipse. r p is the radius at periapsis (or "perifocus" etc.), the closest distance.
Figure 5: Illumination zones (at least 10° elevation) from a Molniya orbit. At apogee, the green illumination zone applies. At three hours before or after apogee, the red zone applies. At four hours before or after apogee, the blue zone applies. The plane of the figure is the longitudinal plane of apogee rotating with the Earth.
Perigee is a type of apsis: an extreme point in an object's orbit. Perigee may also refer to: Perigee: Publication for the Arts, a quarterly literary journal; Holcomb Perigee, a prototype sportsplane; Perigee Books, a former imprint of Penguin Group, now part of TarcherPerigee