Poor Richard's Almanac

celestial_navigation_gmt.py

# -*- coding: utf-8 -*-
# calculate GMT offset given:
# - lunar center's arc distance from sun center, measured locally at noon
# - lunar center's arc distance from sun center, measured at Greenwich at noon
# - lunar center's arc distance from sun center, measured at Greenwich at 3PM

def angle_to_float(deg, min, sec):
    return deg + min/60.0 + sec/3600.0

def gmt_from_lunar(angle_local_tup, angle_greenwich_tup, angle_greenwich_3pm_tup):
    '''each tup (<deg>, <min>, <sec>)'''
    angle_local = angle_to_float(*angle_local_tup)
    angle_greenwich = angle_to_float(*angle_greenwich_tup)
    hr_arcdiff = (angle_to_float(*angle_greenwich_3pm_tup)-angle_greenwich) / 3.0
    print "hour arcdiff:", hr_arcdiff
    return (angle_local - angle_greenwich) / hr_arcdiff


if __name__ == "__main__":
    data = {
        2: [(78,13,52),(84,45,40),(86,23,56)],
        3: [(53,53,19),(56,48,24),(58,15,28)],
        6: [(74,14,7),(71,32,58),(73,3,21)],
        7: [(49,49,13),(44,42,27),(42,59,34)],
        8: [(82,29,26),(85,43,56),(87,20,48)],
    }
    for case_number, tuples in data.iteritems():
        print "CASE #%d"%case_number
        gmt = gmt_from_lunar(*tuples)
        print "GMT:", gmt