David Muir Sharnoff > Time-ParseDate-2013.1113 > Time::JulianDay

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Module Version: 2011.0505   Source  

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.

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.

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.

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