# man > Time::JulianDay

## NAME
    [Time::JulianDay](https://www.chedong.com/phpMan.php/perldoc/Time%3A%3AJulianDay/markdown) -- Julian calendar manipulations

## SYNOPSIS
            use [Time::JulianDay](https://www.chedong.com/phpMan.php/perldoc/Time%3A%3AJulianDay/markdown)

            $jd = julian_day($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](https://www.chedong.com/phpMan.php/perldoc/Time%3A%3AJulianDay/markdown) is not a correct implementation. There are two problems. The first problem is
    that [Time::JulianDay](https://www.chedong.com/phpMan.php/perldoc/Time%3A%3AJulianDay/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/Astro%3A%3ATime/markdown) that may be more accurate.

## GENESIS
    Written by David Muir Sharnoff <<cpan@dave.sharnoff.org>> with help from previous work by Kurt
    Jaeger aka PI <<zrzr0111@helpdesk.rus.uni-stuttgart.de>> based on postings from: Ian Miller
    <<ian_m@cix.compulink.co.uk>>; Gary Puckering <garyp%<cognos.uucp@uunet.uu.net>> based on Collected
    Algorithms of the ACM ?; and the unknown-to-me author of [Time::Local](https://www.chedong.com/phpMan.php/perldoc/Time%3A%3ALocal/markdown).

## LICENSE
    Copyright (C) 1996-1999 David Muir Sharnoff. License hereby granted for anyone to use, modify or
    redistribute this module at their own risk. Please feed useful changes back to
    <cpan@dave.sharnoff.org>.