The shortest path between two points on a plane is a straight line. On the surface
of a sphere, however, there are no straight lines. The shortest path between two
points on the surface of a sphere is given by the arc of the great circle passing
through the two points. A great circle is defined to be the intersection with
a sphere of a plane containing the center of the sphere.

This tool uses Google Map API Tool to draw great circle between any two points
on earth surface. Simply click on any points and then click the next point, this
program will automatically craw the great circle. Also on bottom of the page you
can list of all the distances between two points you selected and longitude and
latitude of the mouse position.