or sphere is of the approximate limit to the secondary mass's "gravitational dominance", a limit defined by "the extent" of its Hill sphere, which is represented mathematically as follows:
:,where, in this representation, semi-major axis "" can be understood as the "instantaneous heliocentric distance" between the two masses (elsewhere abbreviated rp).

More generally, if the less massive body, , orbits a more massive body, (e.g., as a planet orbiting around the Sun), and has a semi-major axis