jd2cal.py

import numpy

def jd2cal(jd):
#% JD2CAL  Converts Julian date to calendar date using algorithm
#%   from "Practical Ephemeris Calculations" by Oliver Montenbruck
#%   (Springer-Verlag, 1989). Must use astronomical year for B.C.
#%   dates (2 BC = -1 year). Non-vectorized version. See also CAL2JD,
#%   DOY2JD, GPS2JD, JD2DOW, JD2DOY, JD2GPS, JD2YR, YR2JD.
#% Version: 24 Apr 99
#% Usage:   [year, month, day]=jd2cal(jd)
#% Input:   jd - Julian date
#% Output:  year - year of calendar date
#%          month - month of calendar date
#%          day - day of calendar date (including decimal)

#% Copyright (c) 2011, Michael R. Craymer
#% All rights reserved.
#% Email: mike@craymer.com
    year = -1
    month = -1
    day = -1

    if jd < 0:
        print('Julian date must be greater than or equal to zero')
        return([year, month, day])

    a = numpy.fix(jd+0.5)

    if a < 2299161:
        c = a + 1524
    else:
        b = numpy.fix((a-1867216.25) / 36524.25)
        c = a + b - numpy.fix(b/4) + 1525

    d = numpy.fix((c-122.1)/365.25)
    e = numpy.fix(365.25*d)
    f = numpy.fix((c-e)/30.6001)
    day = c - e - numpy.fix(30.6001*f) + numpy.remainder((jd+0.5), a)
    month = f - 1 - 12*numpy.fix(f/14)
    year = d - 4715 - numpy.fix((7+month)/10)

    return([year, month, day])