julian.py

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##
# 
# Julian day routines from Meeus, "Astronomical Formulae for Calculators".
# The routines are:
# 
#     Julian(month, day, year)            Integer Julian day number
#     JulianAstro(month, day, year)       Astronomical Julian day number
#     JulianToMonthDayYear(julian_day)    Returns month, day, year tuple
#     DayOfWeek(month, day, year)         0 = Sunday
#     DayOfYear(month, day, year)         1 to 365 (366 in leap year)
#     IsValidDate(month, day, year)       Returns true if date is valid Gregorian
#     IsLeapYear(year)                    Returns true if year is leap year
#     NumDaysInMonth(month, year)
# 
# The JulianAstro function returns the astronomical form and is returned
# as a floating point number.  The astronomical Julian day begins at
# Greenwich mean noon.  The Julian() function returns the more usual
# Julian day as an integer; it is gotten from the astronomical form by
# adding 0.55 and taking the integer part.
# 
# Warning:  In general, the functions do _not_ check their incoming parameters.
# 
# Don Peterson 30 May 1998
# 
# Copyright (C) 2002 GDS Software
# 
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of
# the License, or (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public
# License along with this program; if not, write to the Free
# Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA  02111-1307  USA
# 
# See http://www.gnu.org/licenses/licenses.html for more details.
# 

__version__ = "$Id: julian.py,v 1.3 2002/08/21 12:41:48 donp Exp $"

def NumDaysInMonth(month, year):
    if month == 2:
        if IsLeapYear(year):
            return 29
        else:
            return 28
    elif month == 9 or month == 4 or month == 6 or month == 11:
        return 30
    elif month == 1 or month == 3 or month == 5 or month == 7 or          month == 8 or month == 10 or month == 12:
        return 31
    else:
        raise "Bad month"

def JulianToMonthDayYear(julian_day):
    if julian_day < 0:  raise "Bad input value"
    jd = julian_day + 0.5
    Z = int(jd)
    F = jd - Z
    A = Z
    if Z >= 2299161:
        alpha = int((Z - 1867216.26)/36254.25)
        A = Z + 1 + alpha - int(alpha/4)
    B = A + 1524
    C = int((B - 122.1)/365.25)
    D = int(365.25 * C)
    E = int((B - D)/30.6001)
    day = B - D - int(30.6001 * E) + F
    if E < 13.5:
        month = int(E - 1)
    else:
        month = int(E - 13)
    if month > 2.5:
        year = int(C - 4716)
    else:
        year = int(C - 4715)
    return month, day, year

def DayOfYear(month, day, year):
    if IsLeapYear(year):
        n = int((275*month)/9 -   ((month + 9)/12) + int(day) - 30)
    else:
        n = int((275*month)/9 - 2*((month + 9)/12) + int(day) - 30)
    if n < 1 or n > 366:  raise "Internal error"
    return n

def DayOfWeek(month, day, year):
    julian = int(JulianAstro(month, int(day), year) + 1.5)
    return julian % 7

def IsLeapYear(year):
    if (year % 400 == 0) or (year % 4 == 0 and year % 100 != 0):
        return 1
    else:
        return 0

##
# Returns true if the year is later than 1752 and the month and day
#     numbers are valid.
#     
def IsValidDate(month, day, year):
    if month < 1 or month > 12: return 0
    if int(month) != month    : return 0
    if year < 1753            : return 0
    if day  < 1.0             : return 0
    if int(day) != day:
        if month == 2:
            if IsLeapYear(year):
                if day >= 30.0: return 0
            else:
                if day >= 29.0: return 0
        elif month == 9 or month == 4 or month == 6 or month == 11:
            if day >= 31.0    : return 0
        else:
            if day >= 32.0    : return 0
    else:
        if month == 2:
            if IsLeapYear(year):
                if day >= 29  : return 0
            else:
                if day >= 28  : return 0
        elif month == 9 or month == 4 or month == 6 or month == 11:
            if day >= 30      : return 0
        else:
            if day >= 31      : return 0
    return 1

def JulianAstro(month, day, year):
    "Note that day can be either an integer or a float."
    if month < 3:
        year  = year - 1
        month = month + 12
    julian = int(365.25*year) + int(30.6001*(month+1)) + day + 1720994.5
    tmp = year + month / 100.0 + day / 10000.0
    if tmp >= 1582.1015:
        A = year / 100
        B = 2 - A + A/4
        julian = julian + B
    return julian * 1.0

def Julian(month, day, year):
    return int(JulianAstro(month, day, year) + 0.55)
        
def Test():
    if Julian(12, 31, 1989)        != 2447892   :  raise "TestError"
    if Julian(1, 1, 1990)          != 2447893   :  raise "TestError"
    if Julian(7, 4, 1776)          != 2369916   :  raise "TestError"
    if Julian(2, 29, 2000)         != 2451604   :  raise "TestError"
    if JulianAstro(1, 27.5, 333)   != 1842713.0 :  raise "TestError"
    if JulianAstro(10, 4.81, 1957) != 2436116.31:  raise "TestError"
    if DayOfWeek(11, 13, 1949)     != 0         :  raise "TestError"
    if DayOfWeek( 5, 30, 1998)     != 6         :  raise "TestError"
    if DayOfWeek( 6, 30, 1954)     != 3         :  raise "TestError"
    if DayOfYear(11, 14, 1978)     != 318       :  raise "TestError"
    if DayOfYear( 4, 22, 1980)     != 113       :  raise "TestError"

    month, day, year = JulianToMonthDayYear(2436116.31)
    if month != 10   : raise "TestError"
    if year  != 1957 : raise "TestError"
    if abs(day - 4.81) > .00001 : raise "TestError"
    month, day, year = JulianToMonthDayYear(1842713.0)
    if month != 1    : raise "TestError"
    if year  != 333  : raise "TestError"
    if abs(day - 27.5) > .00001 : raise "TestError"
    month, day, year = JulianToMonthDayYear(1507900.13)
    if month != 5    : raise "TestError"
    if year  != -584 : raise "TestError"
    if abs(day - 28.63) > .00001 : raise "TestError"

    if NumDaysInMonth( 1, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth( 2, 1999) != 28 :  raise "TestError"
    if NumDaysInMonth( 3, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth( 4, 1999) != 30 :  raise "TestError"
    if NumDaysInMonth( 5, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth( 6, 1999) != 30 :  raise "TestError"
    if NumDaysInMonth( 7, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth( 8, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth( 9, 1999) != 30 :  raise "TestError"
    if NumDaysInMonth(10, 1999) != 31 :  raise "TestError"
    if NumDaysInMonth(11, 1999) != 30 :  raise "TestError"
    if NumDaysInMonth(12, 1999) != 31 :  raise "TestError"

    if NumDaysInMonth( 1, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth( 2, 2000) != 29 :  raise "TestError"
    if NumDaysInMonth( 3, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth( 4, 2000) != 30 :  raise "TestError"
    if NumDaysInMonth( 5, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth( 6, 2000) != 30 :  raise "TestError"
    if NumDaysInMonth( 7, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth( 8, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth( 9, 2000) != 30 :  raise "TestError"
    if NumDaysInMonth(10, 2000) != 31 :  raise "TestError"
    if NumDaysInMonth(11, 2000) != 30 :  raise "TestError"
    if NumDaysInMonth(12, 2000) != 31 :  raise "TestError"

if __name__ == "__main__":
    Test()