dms(d, m, s) := (d + m/60 + s/3600)*%pi/180$

great_circle_distance(lat1, long1, lat2, long2) :=
   12742*asin(sqrt(sin((lat2 - lat1)/2)^2 + cos(lat1)*cos(lat2)*sin((long2 - long1)/2)^2))$

/* Coordinates are found here:
      http://www.airport-data.com/airport/BNA/
      http://www.airport-data.com/airport/LAX/   */

great_circle_distance(dms( 36,  7, 28.10), -dms( 86, 40, 41.50),
                      dms( 33, 56, 32.98), -dms(118, 24, 29.05)), numer;
/* 2886.326609413624 */