# Great Circles

Could somebody please please explain how to work out the minimum distance between two co-ordinates on the earth, eg hobart(43 S,147 E) to Beijing (39 N, 117 E). Apparently there is a method incorporating great circles which finds min distant. If anyone knows the formula and could give me a quick explanation, would be much appreciated.
Cheers

Yes, the shortest distance between two points on the surface of a sphere is along a "great circle" which is a circle having the center of the sphere as its center. The length of an arc of radius R and subtending central angle $\theta$, in radians, is R$/theta$. If $\theta$ is in degrees that is $R\theta (\pi/180)$. Here R is the radius of the earth and you will need to work out the angle $\theta$ from the latitude and longitude.