NAME

       DateTime::Format::Epoch::JD - Convert DateTimes to/from Julian Days

SYNOPSIS

         use DateTime::Format::Epoch::JD;

         my $dt = DateTime::Format::Epoch::JD->parse_datetime( 2453244.5 );
          # 2004-08-27T00:00:00
         DateTime::Format::Epoch::JD->format_datetime($dt);
          # 2453244.5

         my $formatter = DateTime::Format::Epoch::JD->new();
         my $dt2 = $formatter->parse_datetime( 2453244.5 );
          # 2004-08-27T00:00:00
         $formatter->format_datetime($dt2);
          # 2453244.5

DESCRIPTION

       This module can convert a DateTime object (or any object that can be converted to a
       DateTime object) to the Julian Day number. This is the number of days since noon U.T.C. on
       January 1, 4713 B.C. (Julian calendar).

       This time scale was originally proposed by John Herschel, and is often used in
       astronomical calculations.

       Similar modules are:

       •   DateTime::Format::Epoch::MJD

           Implements the "modified Julian Day", starting at midnight U.T.C., November 17, 1858.
           This number is always 2,400,000.5 lower than the JD, and this count only uses five
           digits to specify a date between 1859 and about 2130.

       •   DateTime::Format::Epoch::RJD

           Implements the "reduced Julian Day", starting at noon U.T.C., November 16, 1858.  This
           number is always 2,400,000 lower than the JD.

       •   DateTime::Format::Epoch::TJD

           Implements the "truncated Julian Day", starting at midnight U.T.C., May 24, 1968.
           This number is always 2,440,000,5 lower than the JD.  Actually, there is another
           version of the TJD, defined as JD modulo 10,000.  But that one is a bit harder to
           implement, so you'll have to do with this version of TJD.  Or don't use TJD's at all.

       •   DateTime::Format::Epoch::RataDie

           Implements the Rata Die count, starting at January 1, 1 (Gregorian).  This count is
           used by DateTime::Calendar programmers.

       •   DateTime::Format::Epoch::Lilian

           Implements the Lilian count, named after Aloysius Lilian (a 16th century physician)
           and first used by IBM (a 19th century punched card machine manufacturer).  This counts
           the number of days since the adoption of the Gregorian calendar.  Only days are
           counted, and October 15, 1584 is day 1.

METHODS

       Most of the methods are the same as those in DateTime::Format::Epoch.  The only difference
       is the constructor.

       •   new()

           Constructor of the formatter/parser object. It has no parameters.

SUPPORT

       Support for this module is provided via the datetime@perl.org email list. See
       http://lists.perl.org/ for more details.

AUTHOR

       Eugene van der Pijll <pijll@gmx.net>

COPYRIGHT

       Copyright (c) 2004 Eugene van der Pijll.  All rights reserved.  This program is free
       software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

       DateTime

       datetime@perl.org mailing list