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1. Periapsis

   Linked via "two-body systems"

   Nomenclature and General Definition
   In the context of two-body systems governed by the inverse-square law of gravitation, the path of the orbiting body is a conic section. For bound orbits (ellipses), the periapsis marks the minimum radial distance, denoted $r_p$.
   The general form of the term is $\text{peri} + \text{suffix}$, where the prefix peri- derives from the Ancient Greek $\pi\epsilon\rho\iota$ (peri), meaning "near" or "around." The suff…