A great circle is a circle on the surface of a sphere that has the same circumference as the sphere, dividing the sphere into two equal hemispheres. It is a circle on the sphere's surface whose centre is the same as the centre of the sphere. A great circle can also be defined as the intersection of a sphere with a plane going through its center. It is always the largest circle that can be drawn on a given sphere. All great circles have the same radius, which is equal to the radius of the sphere. See also Small Circle.