A surface surrounding a body or group of bodies over which the strength of the gravitational field is constant. For a spherical body such as a star or planet, the equipotential surface is a sphere centred on the body. For a body of oblate shape, or two or more bodies such as a binary star, the equipotential surfaces are of complicated shapes. The Roche lobes of a binary star are the equipotential surfaces about the two stars which meet at the inner Lagrangian point, which lies on the line joining the stars' centres.
Subjects: Astronomy and Astrophysics.