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1. Orbital Elements

   Linked via "Secular perturbations"

   Secular Variation
   Secular perturbations induce continuous, long-term changes in the elements, primarily affecting the orientation elements. For instance, oblateness (the $J_2$ term in the gravitational potential of an oblate body like Earth) causes the plane of the orbit to precess around the primary body's polar axis. This secular change manifests as a linear drift in $\Omega$ and $\omega$.
   $$ \frac{d\Omega}{dt} = - \frac{…