perldoc > Time::JulianDay

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📘 NAME

Time::JulianDay — Julian calendar manipulations

🚀 Quick Reference

Use Case	Command	Description
Get Julian Day from date	julian_day($year, $month, $day)	Convert Gregorian date to Julian Day Number
Get local Julian Day from epoch	local_julian_day($seconds)	Convert seconds since 1970 to local Julian Day
Get GMT Julian Day from epoch	gm_julian_day($seconds)	Convert seconds since 1970 to GMT Julian Day
Get date from Julian Day	inverse_julian_day($jd)	Convert Julian Day to year, month, day
Get day of week	day_of_week($jd)	Day of week (0=Sunday, 6=Saturday)
Convert Julian Day to local seconds	jd_secondslocal($jd, $hour, $min, $sec)	Seconds since 1970 from Julian Day and time (local)
Convert Julian Day to GMT seconds	jd_secondsgm($jd, $hour, $min, $sec)	Seconds since 1970 from Julian Day and time (GMT)
Convert local time to seconds	jd_timelocal($sec,$min,$hours,$mday,$month_0_to_11,$year)	Inverse of localtime using month 0–11
Convert GMT time to seconds	jd_timegm($sec,$min,$hours,$mday,$month_0_to_11,$year)	Inverse of gmtime using month 0–11

📖 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 AT dave.org> with help from previous work by Kurt Jaeger aka PI <zrzr0111 AT helpdesk.de> based on postings from: Ian Miller <ian_m AT cix.uk>; Gary Puckering <garyp%cognos.uucp AT uunet.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 AT dave.org.

📘 NAME 🚀 Quick Reference 📖 SYNOPSIS 📝 DESCRIPTION ⚠️ ERRATA 📜 GENESIS 📄 LICENSE