1911 Encyclopædia Britannica/Great Circle

GREAT CIRCLE. The circle in which a sphere is cut by a plane is called a “great circle,” when the cutting plane passes through the centre of sphere. Treating the earth as a sphere, the meridians of longitude are all great circles. Of the parallels of latitude, the equator only is a great circle. The shortest line joining any two points is an arc of a great circle. For “great circle sailing” see Navigation.