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…
Ascending node (orbital mechanics) Ascending node The ascending node is the point where an orbiting body crosses a chosen reference plane from south to north; its longitude (Ω) fixes the orbit’s orientation and is one of the class…
Astrodynamics: Motion, Orbits, and Spacecraft Navigation Astrodynamics Astrodynamics studies the motion of spacecraft and natural bodies under gravity and other forces, covering orbital mechanics, maneuvers, trajectory design, and applications from sa…
Astrometry: Measuring Positions, Motions and Distances of Celestial Bodies Astrometry Astrometry is the branch of astronomy that precisely measures the positions, motions and distances of celestial objects using techniques such as proper motion and parallax, underpi…
