An Etymological Dictionary of Astronomy and Astrophysics

An imaginary surface surrounding a body, or group of bodies, over which the gravitational field is of constant strength and, at all points, is directed perpendicular to the surface. For a single star the surface is spherical. In a close binary system the equipotential surface of the components interact to become hourglass-shaped. → Roche lobe;
→ Lagrangian points.

See also: From → equi-; → potential; → surface.