Apsis (astronomy): periapsis, apoapsis, and the line of apsides Apsis An apsis is the extreme point in an orbit — nearest (periapsis) or farthest (apoapsis) — with named variants for different central bodies and importance in orbital mechanics and ce…
Argument of periapsis The argument of periapsis is an orbital element measuring the angle from the ascending node to the orbit's periapsis; it locates where closest approach occurs and helps describe or…
