Function skyDistance( lon1, lat1, lon2, lat2 )

Description:
Calculates the separation (distance around a great circle) of two points on the sky in degrees.

This function is identical to skyDistanceDegrees in class CoordsDegrees.

Parameters:
lon1 (floating point)
point 1 longitude in degrees
lat1 (floating point)
point 1 latitude in degrees
lon2 (floating point)
point 2 longitude in degrees
lat2 (floating point)
point 2 latitude in degrees
Return Value (floating point):
angular distance between point 1 and point 2 in degrees
Signature:
double skyDistance(double, double, double, double)