DateTime-Event-Easter

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lib/DateTime/Event/Easter.pm  view on Meta::CPAN

=head1 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 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.

=head1 CONSTRUCTOR

=head2 C<new> constructor

This class accepts the following options to its C<new> constructor:

lib/DateTime/Event/Easter.pm  view on Meta::CPAN

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.

=item * 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 C<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
C<25>, while "alternate 25" is printed  in a way that distinguishes it
from the other  numbers. Jean Lefort mentions C<XXV>  or using italics
or bold  digits, such as  B<C<25>>. This module prints  the "alternate
25" as "C<25*>".

=item * eastern_epact($year)

In the Julian comput, the epact  is the age of the ecclesiastical Moon
on 22nd March. The C<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.

lib/DateTime/Event/Easter.pm  view on Meta::CPAN

=head1 THE SMALL PRINT

=head2 REFERENCES

=over 4

=item * L<https://github.com/houseabsolute/DateTime.pm/wiki> - The official wiki
of the DateTime project

=item * L<https://www.tondering.dk/claus/calendar.html> - Claus Tøndering's
calendar FAQ, especially the page L<https://www.tondering.dk/claus/cal/easter.php>.

=item * I<Calendrical Calculations> (Third or Fourth Edition) by Nachum Dershowitz and
Edward M. Reingold, Cambridge University Press, see
L<http://www.calendarists.com>
or L<https://www.cambridge.org/us/academic/subjects/computer-science/computing-general-interest/calendrical-calculations-ultimate-edition-4th-edition?format=PB&isbn=9781107683167>,
ISBN 978-0-521-70238-6 for the third edition.

=item * I<La saga des calendriers>, by Jean Lefort, published by I<Belin> (I<Pour la Science>), ISBN 2-90929-003-5
See L<https://www.belin-editeur.com/la-saga-des-calendriers>

=item * I<Le Calendrier>, by Paul Couderc, published by I<Presses universitaires de France> (I<Que sais-je ?>), ISBN 2-13-036266-4
See L<https://catalogue.bnf.fr/ark:/12148/cb329699661>.

=back

lib/DateTime/Event/Easter.pm  view on Meta::CPAN

Rick Measham <rickm@cpan.org>

Co-maintainer Jean Forget <jforget@cpan.org>

=head2 CREDITS

Much help from the DateTime mailing list, especially from:

B<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

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

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

B<Joe Orost> and B<Andreas König> - for RT tickets about the POD documentation

B<Frank Wiegand> and B<Slaven Rezić> - for patches fixing the POD problems

B<Tom Wyant> -  for a constructive dialog about  the relations between