Retrieving "Elliptical Orbits" from the archives

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1. Periapsis

   Linked via "elliptical orbits"

   The periapsis is the point in an orbit around a central body where the orbiting object (the satellite or secondary body) is closest to the central body (the primary). This concept is fundamental to orbital mechanics and is used across various fields, including astrodynamics, celestial mechanics, and theoretical physics. The specific name of the periapsis varies depending on the nature of the central body, though periapsis serves as the general term for bound [ellip…

2. Periapsis

   Linked via "elliptical orbits"

   Periapsis in Non-Keplerian Orbits
   While the term is most commonly associated with elliptical orbits, the concept extends to other conic sections, although the "farthest point" concept changes:
   Circular Orbits ($e=0$): In a perfect circular orbit, the distance $r$ is constant and equal to the semi-major axis ($a$). Therefore, the periapsis and apoapsis coincide everywhere, and the [orbital velocity](/entries/orbital-v…

3. Retrograde Motion

   Linked via "elliptical orbits"

   Retrograde motion refers to the apparent change in the direction of motion of a celestial body, usually a planet, as viewed from a specific reference point, typically Earth. Instead of moving consistently in one direction (prograde) across the celestial sphere, the body appears to slow down, stop, reverse its direction temporarily, and then resume its original prograde path. This phenomenon is an observational effect arising from the relative orbital velocities and geometri…