Astrophysics (Index)About

apsis

(closest or furthest point in an eccentric orbit)

An apsis of an orbit with some eccentricity is either its closest point to the object being orbited (periapsis or periapse) or the furthest point (apoapsis or apapsis or apoapse). The terms pericenter and apocenter similarly mean the closest and furthest points in the orbit from the orbit's center of mass. Specific terms are used for bodies orbiting some specific hosts, such as the Earth or Sun, which are familiar and occasionally used for other hosts:

The argument of periapsis (or argument of perifocus or argument of pericenter, or incorporating terms for orbits of a specific body, such as argument of perihelion for an orbit around the Sun) is an angle describing where the periapsis is in relation to a reference plane. For example, if a comet's orbit is inclined to the ecliptic (the plane of Earth's orbit, a common reference plane for the solar system), then the argument of periapsis is the angle at the Sun (within the plane of the comet's orbit) from the direction toward the orbit's intersection with the ecliptic to the direction toward the comet's perihelion. If the comet's argument of periapsis is zero degrees, then its periapsis is on the ecliptic. If it is ninety degrees, then the periapsis is as far away from the ecliptic is it could be given the comet's eccentricity and orbital plane.


(orbits,celestial mechanics)
Further reading:
https://en.wikipedia.org/wiki/Apsis
https://en.wikipedia.org/wiki/Argument_of_periapsis
https://astronomy.swin.edu.au/cosmos/A/Apoapsis
https://astronomy.swin.edu.au/cosmos/p/Periapsis
https://www.physics.unlv.edu/~jeffery/astro/orbit/orbit_apsis.html

Referenced by pages:
anomalistic year
astronomical unit (AU)
black hole merger
Comet Shoemaker-Levy 9
eccentricity (e)
Mars crosser (MC)
mean anomaly
Mercury
moon
orbital element
Parker Solar Probe (PSP)
precession
quenched galaxy
Sedna
sidereal
Solar Orbiter (SolO)
trans-Neptune object (TNO)

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