# why is there not a <pseudocode> tag :) ?
# here is the triangle we solve...
#
#     A (North Pole)
#    / \
#   c   b
#  /     \
# B---a---C
#
# Point A is the north pole, B an C are all yours
# $pointB $latB, $longB
# $pointC $latC, $longC
# here is the formula
# cos a = cos b * cos c + sin b * sin c + cos A

$miles_per_degree=$Earths_Circumference/360;
$Angle_A=abs($longB - $longC); # needs fix for wrapping round the prime meridian
$Len_b = (90-LongC)*$miles_per_degree; # fix for south of equator
$Len_c = (90-LongB)*$miles_per_degree; # make degrees S negative ?

# plug those three into the spherical circle equasion