Great circle - Wikipedia, the free encyclopedia
A
great circle, also known as a
Riemannian circle, of a
sphere is the intersection of the sphere and a
plane which passes through the center point of the sphere, as distinct from a
small circle.
For any two points on the surface of a sphere there is a great circle through the two points. The minor arc of a great circle between two points is the shortest surface-path between them.
Strictly speaking the Earth
is not a perfect sphere (it is an oblate spheroid or ellipsoid – i.e., slightly compressed at the poles), which means that the shortest distance between two points (a geodesic) is not quite a great circle. Nevertheless, the sphere model can be considered a first approximation.
Great circle routes are used by ships and aircraft where currents and winds are not a significant factor.
Flight lengths can therefore often be approximated to the
great-circle distance between two airports. For aircraft travelling west between continents in the northern hemisphere these paths will extend northward near or into the
Arctic region, however easterly flights will often fly a more southerly track to take advantage of the
jet stream.