era.jd2cal.md

eraJd2cal

[rv, iy, im, id, fd] = ERFA.jd2cal(dj1, dj2)

Julian Date to Gregorian year, month, day, and fraction of a day.

Given:

   dj1,dj2   double   Julian Date (Notes 1, 2)

Returned (arguments):

   iy        int      year
   im        int      month
   id        int      day
   fd        double   fraction of day

Returned (function value):

             int      status:
                         0 = OK
                        -1 = unacceptable date (Note 1)

Notes:

1. The earliest valid date is -68569.5 (-4900 March 1). The largest value accepted is 1e9.

2. The Julian Date is apportioned in any convenient way between the arguments dj1 and dj2. For example, JD=2450123.7 could be expressed in any of these ways, among others:

          dj1             dj2

       2450123.7           0.0       (JD method)
       2451545.0       -1421.3       (J2000 method)
       2400000.5       50123.2       (MJD method)
       2450123.5           0.2       (date & time method)

Separating integer and fraction uses the "compensated summation" algorithm of Kahan-Neumaier to preserve as much precision as possible irrespective of the jd1+jd2 apportionment.

3. In early eras the conversion is from the "proleptic Gregorian calendar"; no account is taken of the date(s) of adoption of the Gregorian calendar, nor is the AD/BC numbering convention observed.

References:

Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann (ed), University Science Books (1992), Section 12.92 (p604).

Klein, A., A Generalized Kahan-Babuska-Summation-Algorithm. Computing, 76, 279-293 (2006), Section 3.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.