Originally Posted by RatherBeFlying
Not quite so sure about that as, with the exception of lasers, electromagnetic radiation likes to propagate on a spherical wavefront.
A great circle is the shortest distance between two points along the surface of the Earth ignoring any mountain ranges. A great circle taken all the way round between said two points effectively divides the Earth into two equal hemispheres -- the Equator being one case; others being any line of longitude paired with its opposite number (+ or - 180 degrees).
But is Earth a sphere?
On a sphere, two points are connected by 1 shortest path, which is an arc of the great circle in the plane of those two points and the centre of Earth. Except two antipodeal points, in which case all great circles through either point are equally shortest connecting paths.
But the Earth is not a sphere... 2 poles are connected by infinite number of equally shortest paths (all meridians), but 2 opposite points of equator are connected by 2 equally shortest paths - the meridians. The arcs of equator between those points are longer!