NAME

DateTime::Event::Easter - Returns Easter events for DateTime objects

SYNOPSIS

use DateTime::Event::Easter;

$dt = DateTime->new( year   => 2002,
                     month  => 3,
                     day    => 31,
                   );


$easter_sunday = DateTime::Event::Easter->new();

$previous_easter_sunday = $easter_sunday->previous($dt);
# Sun, 15 Apr 2001 00:00:00 UTC

$following_easter_sunday = $easter_sunday->following($dt);
# Sun, 20 Apr 2003 00:00:00 UTC

$closest_easter_sunday = $easter_sunday->closest($dt);
# Sun, 31 Mar 2002 00:00:00 UTC

$is_easter_sunday = $easter_sunday->is($dt);
# 1

$palm_sunday = DateTime::Event::Easter->new(day=>'Palm Sunday');


$dt2 = DateTime->new( year   => 2060,
                      month  => 4,
                      day    => 30,
                    );

@set = $palm_sunday->set(from=>$dt, to=>$dt2, inclusive=>1);
# Sun, 13 Apr 2003 00:00:00 UTC
# Sun, 04 Apr 2004 00:00:00 UTC
# Sun, 20 Mar 2005 00:00:00 UTC
# Sun, 09 Apr 2006 00:00:00 UTC

DESCRIPTION

The DateTime::Event::Easter module returns Easter events for DateTime objects. From a given datetime, it can tell you the previous, the following and the closest Easter event. The 'is' method will tell you if the given DateTime is an Easter Event.

Easter Events can be Palm Sunday, Maundy Thursday, Good Friday, Black Saturday and Easter Sunday. If that's not enough, the module will also accept an offset so you can get the date for Pentecost (49 days after Easter Sunday) by passing 49.

BACKGROUND

Easter Sunday is the Sunday following the first full moon on or following the Official Vernal Equinox. The Official Vernal Equinox is March 21st. Easter Sunday is never on the full moon. Thus the earliest Easter can be is March 22nd.

In the orthodox world, although they now use the Gregorian Calendar rather than the Julian, they still take the first full moon after the Julian March 21st. As the Julian calendar is slowly getting further and further out of sync with the Gregorian, the first full moon after this date can be a completely different one than for the western Easter. This is why the Orthodox churches celebrate Easter later than western churches.

CONSTRUCTOR

This class accepts the following options to its 'new' constructor:

• easter => ([western]|eastern)

  DateTime::Event::Easter understands two calculations for Easter. For simplicity we've called them 'western' and 'eastern'.

  Western Easter is the day celebrated by the Catholic and Protestant churches. It falls on the first Sunday on or after the the first Full Moon after March 21st.

  Eastern Easter, as celebrated by the Eastern Orthodox Churches similarly falls on the first Sunday on or after the the first Full Moon after March 21st. However Eastern Easter uses March 21st in the Julian Calendar.

  By default this module uses the Western Easter. Even if you pass a Julian DateTime to the module, you'll get back Western Easter unless you specifically ask for Eastern.

  If this parameter is not supplied, the western Easter will be used.

• day => ([Easter Sunday]|Palm Sunday|Maundy Thursday|Good Friday|Black Saturday|n)

  When constructed with a day parameter, the method can return associated Easter days other than Easter Sunday. The constructor also allows an integer to be passed here as an offset. For example, Maundy Thursday is the same as an offset of -3 (Three days before Easter Sunday)

  When constructed without a day parameter, the method uses the date for Easter Sunday (which is the churches' official day for 'Easter', think of it a 'Easter Day' if you want)

  This parameter also allows the following abreviations: day => ([Sunday]|Palm|Thursday|Friday|Saturday)

METHODS

For all these methods, unless otherwise noted, $dt is a plain vanila DateTime object or a DateTime object from any DateTime::Calendar module that can handle calls to from_object and utc_rd_values (which should be all of them, but there's nothing stopping someone making a bad egg).

This class offers the following methods.

• following($dt)

  Returns the DateTime object for the Easter Event after $dt. This will not return $dt.

• previous($dt)

  Returns the DateTime object for the Easter Event before $dt. This will not return $dt.

• closest($dt)

  Returns the DateTime object for the Easter Event closest to $dt. This will return midnight of $dt if $dt is the Easter Event.

• is($dt)

  Return positive (1) if $dt is the Easter Event, otherwise returns false (0)

• as_list(from => $dt, to => $dt2, inclusive=>([0]|1))

  Returns a list of Easter Events between to and from.

  If the optional inclusive parameter is true (non-zero), the to and from dates will be included if they are the Easter Event.

  If you do not include an inclusive parameter, we assume you do not want to include these dates (the same behaviour as supplying a false value)

• as_set(from => $dt, to => $dt2, inclusive=>([0]|1))

  Returns a DateTime::Set of Easter Events between to and from.

  If the optional inclusive parameter is true (non-zero), the to and from dates will be included if they are the Easter Event.

  If you do not include an inclusive parameter, we assume you do not want to include these dates (the same behaviour as supplying a false value)

EXPORTS

This class does not export any methods by default, however the following exports are supported.

• easter($year)

  Given a Gregorian year, this method will return a DateTime object for Western Easter Sunday in that year.

THE SMALL PRINT

REFERENCES

• http://datetime.perl.org - The official home of the DateTime project

• http://www.tondering.dk/claus/calendar.html - Claus Tøndering's calendar FAQ

SUPPORT

Support for this module, and for all DateTime modules will be given through the DateTime mailing list - datetime@perl.org.

Bugs should be reported through rt.cpan.org.

AUTHOR

Rick Measham <rickm@cpan.org>

CREDITS

Much help from the DateTime mailing list, especially from:

Eugene van der Pijll - who pointed out flaws causing errors on gregorian years with no eastern easter (like 35000) and who came up with a patch to make the module accept any calendar's DateTime object

Dave Rolsky - who picked nits, designed DateTime itself and leads the project

Martin Hasch - who pointed out the posibility of memory leak with an early beta

COPYRIGHT

(c) Copyright 2003 Rick Measham. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.

SEE ALSO

DateTime, DateTime::Calendar::Easter, perl(1), http://datetime.perl.org.

cpanm DateTime::Event::Easter

perl -MCPAN -e shell
install DateTime::Event::Easter