Periapsis -- from Eric Weisstein's World of Physics

The closest distance a body in orbit about a mass M reaches is called the periapsis and is denoted . The distance from M is then given by

where a is the semimajor axis Eric Weisstein's World of Math, e is the eccentricity, and is the orbital angle. At periapsis, , so

Apoapsis, Perigee, Eric Weisstein's World of Astronomy Perihelion Eric Weisstein's World of Astronomy