Note:  Do not rely on this information. It is very old.

Circle Greatand Small

Circle, Great and Small. Any plane section of a sphere cuts the surface in a circle. Great circles are those obtained when the plane of section passes through the centre of the sphere; lines of longitude and the equator are examples of great circles on the earth. The shortest distance between two points on a sphere is along the great circle containing those points; hence, great-circle sailing in navigation. All other sections of a sphere form small circles: examples of these are seen in the Arctic and Antarctic circles, and in all other lines of latitude excepting the equator.