NAME

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   => 2006,
                        month  =>    4,
                        day    =>   30,
                      );
  
  $set  = $palm_sunday->as_set (from => $dt, to => $dt2, inclusive => 1);
  @list = $palm_sunday->as_list(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
  
  $datetime_set = $palm_sunday->as_set;
  # A set of every Palm Sunday ever. See DateTime::Set for more information.

DESCRIPTION

Easter Events can be Fat Tuesday, Ash Wednesday, Palm Sunday, Maundy Thursday, Good Friday, Black Saturday, Easter Sunday, Ascension, Pentecost and Trinity Sunday. If that's not enough, the module will also accept an offset so you can get the date for Quasimodo (the next sunday after Easter Sunday) by passing 7.

BACKGROUND

In the orthodox world, although they now use the Gregorian Calendar rather than the Julian, they still take the first full moon on or 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

METHODS

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 true (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 from and to.

  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()

  Returns a DateTime::Set of Easter Events.

  In the past this method used the same syntax as 'as_list' above. However we now allow both the above syntax as well as the full options allowable when creating sets with "DateTime::Set". This means you can call "$datetime_set = $palm_sunday->as_set;" and it will return a "DateTime::Set" of all Palm Sundays. See DateTime::Set for more information.

• as_span()

  This method switches output to spans rather than points. See the 'as' attribute of the constructor for more information. The method returns the object for easy chaining.

• as_point()

  This method switches output to points rather than spans. See the 'as' attribute of the constructor for more information. The method returns the object for easy chaining.

• as_old_set()

  Deprecated method.

  In the next version (1.10) or in October 2021 (two years after the v1.08 initial announcement), whichever comes last, this method will emit a warning. And within another two years / one version, this method will be removed.

SUBROUTINES

These elements can be found in various sources, including what is known in France as l'Almanach du Facteur (the postman's almanach). These values are printed at the bottom of the February frame, which is a convenient way to ensure this frame has the same height as the frames for 31-day months.

These subroutines are not exported by default.

• golden_number($year)

  Gives the position of the year in the Metonic cycle. This is a 1..19 number.

  This subroutine applies to both western and eastern computs.

• western_epact($year)

  In the Gregorian comput, the epact is the age of the ecclesiastical Moon on the 1st January of the given year. The "western" part of the subroutine name accounts for the fact that Gregorian and Julian calendars do not use the same formula.

  The epact is a 0..29 number. The "0" value is shown as "*" in some sources. This subroutine does not convert "0" to "*", the result is always a pure number.

  Actually, the western epact is a little more than a number. As explained by Paul Couderc (page 86) and Jean Lefort (page 142), there is a special case for 25, which should be considered as two values, "basic 25" and "alternate 25". "Basic 25" is printed as a plain number 25, while "alternate 25" is printed in a way that distinguishes it from the other numbers. Jean Lefort mentions "XXV" or using italics or bold digits, such as 25. This module prints the "alternate 25" as ""25*"".

• eastern_epact($year)

  In the Julian comput, the epact is the age of the ecclesiastical Moon on 22nd March. The "eastern" part of the subroutine name accounts for the fact that Gregorian and Julian calendars do not use the same formula.

  The epact is a 0..29 number. The "0" value is shown as "*" in some sources. This subroutine does not convert "0" to "*", the result is always a pure number. There is no other special case, for 25 as for any other number.

  The formula given by Reingold and Dershowitz is a "shifted epact" and gives different results from the values printed in Lefort's and Couderc's books. The module follows Couderc and Lefort.

• western_sunday_letter($year), eastern_sunday_letter($year)

  On normal years (that is, excluding leap years), the Sunday letter is determined by tagging 1st January with "A", 2nd January with "B", and so on and looking at the first sunday of the year. The letter found at this sunday if the sunday letter for the year.

  The sunday letter governs all conversions from (mm, dd) to day-of-week. For example, if the letter is "F", then 1st January, 12th February, 2nd July and 1st October, among others, are tuesdays, while 6th January, 24th February, 14th July and 6th October are sundays.

  On leap years, there are two sunday letters. The first one is determined as above, the second one is determined by tagging 2nd January, not 1st, with "A". The first sunday letter governs all conversions from (mm, dd) to day-of-week for January and February only, while the second sunday letter governs the conversions from (mm, dd) to day-of-week for March and after.

  So, if the sunday letters are "FE", 1st January and 12th February are still tuesdays, but 2nd July and 1st October are wednesdays. At the same time, 6th January and 24th February are still sundays, while 14th July and 6th October are mondays.

  "western_sunday_letter" applies only to Gregorian years, while "eastern_sunday_letter" applies only to Julian years.

• western_sunday_number($year), eastern_sunday_number($year)

  Letters (standalone or in pairs) are not convenient for numerical calculations. So the xxx"_sunday_number" subroutine is used instead of xxx"_sunday_letter".

  In case of leap years, the xxx"_sunday_number" subroutine gives the numerical value for the second sunday letter, because Easter never falls in January or February.

• easter($year)

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

• western_easter($year)

  Given a Gregorian year, this subroutine will return a DateTime object for Western Easter Sunday in that year. But unlike the previous subroutine, "western_easter" cannot be imported. You must use its fully qualified name:

    my $date = DateTime::Event::Easter::western_easter($year);
      

• eastern_easter($year)

  Given a Julian year, this subroutine will return a DateTime :: Calendar :: Julian object for Eastern Easter Sunday in that year. And like "western_easter", "eastern_easter" cannot be imported. You must use its fully qualified name:

    my $date = DateTime::Event::Easter::eastern_easter($year);
      

BUGS AND PROBLEMS FOR SPANS

  2017-04-16T00:00:00 to 2017-04-16T23:59:59
  2018-04-01T00:00:00 to 2018-04-01T23:59:59
  2019-04-21T00:00:00 to 2019-04-21T23:59:59
  2020-04-12T00:00:00 to 2020-04-12T23:59:59

  2017-04-16T21:43:00 to 2017-04-16T23:59:59
  2018-04-01T00:00:00 to 2018-04-01T23:59:59
  2019-04-21T00:00:00 to 2019-04-21T23:59:59
  2020-04-12T00:00:00 to 2020-04-12T12:34:00

  2018-04-01T00:00:00 to 2018-04-01T23:59:59
  2019-04-21T00:00:00 to 2019-04-21T23:59:59

  2017-04-16T21:43:01 to 2017-04-16T23:59:59
  2018-04-01T00:00:00 to 2018-04-01T23:59:59
  2019-04-21T00:00:00 to 2019-04-21T23:59:59
  2020-04-12T00:00:00 to 2020-04-12T12:35:59

THE SMALL PRINT