Time::JulianDay(3pm)

NAME
Time::JulianDay -- Julian calendar manipulations

SYNOPSIS
        use Time::JulianDay

        $jd = julian_day($year, $month_1_to_12, $day)
        $jd = local_julian_day($seconds_since_1970);
        $jd = gm_julian_day($seconds_since_1970);
        ($year, $month_1_to_12, $day) = inverse_julian_day($jd)
        $dow = day_of_week($jd)

        print (Sun,Mon,Tue,Wed,Thu,Fri,Sat)[$dow];

        $seconds_since_jan_1_1970 = jd_secondslocal($jd, $hour, $min, $sec)
        $seconds_since_jan_1_1970 = jd_secondsgm($jd, $hour, $min, $sec)
        $seconds_since_jan_1_1970 = jd_timelocal($sec,$min,$hours,$mday,$month_0_to_11,$year)
        $seconds_since_jan_1_1970 = jd_timegm($sec,$min,$hours,$mday,$month_0_to_11,$year)

DESCRIPTION
JulianDay is a package that manipulates dates as number of days since some time a long time ago. It's easy to add and subtract time using julian days...

The day_of_week returned by day_of_week() is 0 for Sunday, and 6 for Saturday and everything else is in between.

ERRATA
Time::JulianDay is not a correct implementation. There are two problems. The first problem is that Time::JulianDay only works with integers. Julian Day can be fractional to represent time within a day. If you call inverse_julian_day() with a non-integer time, it will often give you an incorrect result.

The second problem is that Julian Days start at noon rather than midnight. The julian_day() function returns results that are too large by 0.5.

What to do about these problems is currently open for debate. I'm tempted to leave the current functions alone and add a second set with more accurate behavior.

There is another implementation in Astro::Time that may be more accurate.

AUTHOR
Best Practical Solutions, LLC <modules@bestpractical.com>

ORIGINAL AUTHOR
David Muir Sharnoff

GENESIS
Based on previous work by Kurt Jaeger, Ian Miller, Gary Puckering (based on Collected Algorithms of the ACM), and the author of Time::Local.

LICENSE AND COPYRIGHT
Copyright (C) 1996-1999 David Muir Sharnoff. Copyright (C) 2026 Best Practical Solutions, LLC.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.