

Haversine formula  Facts, Info, and Encyclopedia article (Site not responding. Last check: 20071008) 
  It is a special case of a more general formula in (The trigonometry of spherical triangles) spherical trigonometry, the law of haversines, relating the sides and angles of spherical "triangles". 
  Given a unit sphere, a "triangle" on the surface of the sphere is defined by the (A circular line on the surface of a sphere formed by intersecting it with a plane passing through the center) great circles connecting three points u, v, and w on the sphere. 
  In order to obtain the haversine formula of the previous section from this law, one simply considers the special case where u is the (The northernmost point of the Earth's axis) north pole, while v and w are the two points whose separation d is to be determined. 
 www.absoluteastronomy.com /encyclopedia/h/ha/haversine_formula.htm (832 words) 
