jd2date

JD2DATE Gregorian calendar date from modified Julian day number.

   [YEAR, MONTH, DAY, HOUR, MINUTE, SECOND] = JD2DATE(JD) returns the
   Gregorian calendar date (year, month, day, hour, minute, and second)
   corresponding to the Julian day number JD.

   Start of the JD (Julian day) count is from 0 at 12 noon 1 JAN -4712
   (4713 BC), Julian proleptic calendar.  Note that this day count conforms
   with the astronomical convention starting the day at noon, in contrast
   with the civil practice where the day starts with midnight.

   Astronomers have used the Julian period to assign a unique number to
   every day since 1 January 4713 BC.  This is the so-called Julian Day
   (JD). JD 0 designates the 24 hours from noon UTC on 1 January 4713 BC
   (Julian calendar) to noon UTC on 2 January 4713 BC.

0001 function [year, month, day, hour, minute, second] = jd2date(jd)
0002 %JD2DATE Gregorian calendar date from modified Julian day number.
0003 %
0004 %   [YEAR, MONTH, DAY, HOUR, MINUTE, SECOND] = JD2DATE(JD) returns the
0005 %   Gregorian calendar date (year, month, day, hour, minute, and second)
0006 %   corresponding to the Julian day number JD.
0007 %
0008 %   Start of the JD (Julian day) count is from 0 at 12 noon 1 JAN -4712
0009 %   (4713 BC), Julian proleptic calendar.  Note that this day count conforms
0010 %   with the astronomical convention starting the day at noon, in contrast
0011 %   with the civil practice where the day starts with midnight.
0012 %
0013 %   Astronomers have used the Julian period to assign a unique number to
0014 %   every day since 1 January 4713 BC.  This is the so-called Julian Day
0015 %   (JD). JD 0 designates the 24 hours from noon UTC on 1 January 4713 BC
0016 %   (Julian calendar) to noon UTC on 2 January 4713 BC.
0017 
0018 %   Sources:  - http://tycho.usno.navy.mil/mjd.html
0019 %             - The Calendar FAQ (http://www.faqs.org)
0020 
0021 %   Author:      Peter J. Acklam
0022 %   Time-stamp:  2002-05-24 15:24:45 +0200
0023 %   E-mail:      pjacklam@online.no
0024 %   URL:         http://home.online.no/~pjacklam
0025 
0026    nargsin = nargin;
0027    error(nargchk(1, 1, nargsin));
0028 
0029    % Adding 0.5 to JD and taking FLOOR ensures that the date is correct.
0030    % Here are some sample values:
0031    %
0032    %  MJD     Date       Time
0033    %  -1.00 = 1858-11-16 00:00 (not 1858-11-15 24:00!)
0034    %  -0.75 = 1858-11-16 06:00
0035    %  -0.50 = 1858-11-16 12:00
0036    %  -0.25 = 1858-11-16 18:00
0037    %   0.00 = 1858-11-17 00:00 (not 1858-11-16 24:00!)
0038    %  +0.25 = 1858-11-17 06:00
0039    %  +0.50 = 1858-11-17 12:00
0040    %  +0.75 = 1858-11-17 18:00
0041    %  +1.00 = 1858-11-18 00:00 (not 1858-11-17 24:00!)
0042 
0043    ijd = floor(jd + 0.5);               % integer part
0044 
0045    if nargout > 3
0046       fjd = jd - ijd + 0.5;             % fraction part
0047       [hour, minute, second] = days2hms(fjd);
0048    end
0049 
0050    % The following algorithm is from the Calendar FAQ.
0051 
0052    a = ijd + 32044;
0053    b = floor((4 * a + 3) / 146097);
0054    c = a - floor((b * 146097) / 4);
0055 
0056    d = floor((4 * c + 3) / 1461);
0057    e = c - floor((1461 * d) / 4);
0058    m = floor((5 * e + 2) / 153);
0059 
0060    day   = e - floor((153 * m + 2) / 5) + 1;
0061    month = m + 3 - 12 * floor(m / 10);
0062    year  = b * 100 + d - 4800 + floor(m / 10);