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1. Apogee

   Linked via "nodal regression"

   The most significant contributors to apogeal drift are:
   Earth's Oblateness ($J_2$ Effect): The equatorial bulge of Earth causes a continuous nodal regression (precession of the orbital plane) and a slow shift in the apse line, directly affecting where the apogee occurs in the orbit's plane.
   Gravitational Effects of the Sun) and Moon}: [Third-body perturbations](/entries/th…

2. Oblate Spheroid

   Linked via "nodal regression"

   | Triaxial Ellipsoid | $a \neq b \neq c$ | Three unequal semi-axes (e.g., some minor moons). | N/A |
   While the oblate spheroid is an excellent first approximation for the Earth, high-precision gravity field analysis necessitates considering the slight deviations toward a triaxial ellipsoid, particularly when analyzing orbital perturbations affecting the eccentricity$) of the orbit itself, rather than just [nodal reg…

3. Orbital Mechanics

   Linked via "nodal regression"

   Celestial bodies, especially those with rapid rotation like Earth, exhibit equatorial bulging, described mathematically by the gravitational potential expansion coefficients. The dominant non-spherical term is the second zonal harmonic, $J_2$.
   The presence of $J_2$ causes the orbital plane to precess (the nodal regression and the shift in argument of periapsis). The secular rate of precession of the argument of periapsis ($\dot{\omega}$) for a ne…