Original: The argument of periapsis ( also called argument of perifocus or argument of pericenter ) , symbolized as Ï , is one of the orbital elements of an orbiting body . Specifically , Ï is the angle between the orbit 's periapsis ( the point of closest approach to the central point ) and the orbit 's ascending node ( the point where the body crosses the plane of reference from South to North ) .
Simplified: The argument of periapsis ( Ï ) is the orbital element describing the angle of an orbiting body 's periapsis ( the point of closest approach to the central body ) , relative to its ascending node ( the point where the body crosses the plane of reference from south to north ) .