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.IX Title "Time::JulianDay 3"
.TH Time::JulianDay 3 2023-07-26 "perl v5.38.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH NAME
Time::JulianDay \-\- Julian calendar manipulations
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&        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)
.Ve
.SH DESCRIPTION
.IX Header "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...
.PP
The day_of_week returned by \fBday_of_week()\fR is 0 for Sunday, and 6 for
Saturday and everything else is in between.
.SH ERRATA
.IX Header "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 \fBinverse_julian_day()\fR with a non-integer
time, it will often give you an incorrect result.
.PP
The second problem is that Julian Days start at noon rather than
midnight.  The \fBjulian_day()\fR function returns results that are too
large by 0.5.
.PP
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.
.PP
There is another implementation in Astro::Time that may be more accurate.
.SH GENESIS
.IX Header "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.
.SH LICENSE
.IX Header "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.