A circle on the surface of a sphere produced by any plane which passes through the centre of the sphere and intersects the sphere's surface. (Also called an orthodrome).
The intersection of a plane that passes through the center of a sphere with the surface of that sphere; the largest possible circle that can be drawn on the surface of a sphere.
A circle on the surface of a sphere, which lies in a plane intersecting the center of that sphere. Equatorial ring.