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Date::Doomsday(3)     User Contributed Perl Documentation    Date::Doomsday(3)

       Date::Doomsday -	Determine doomsday for a given year

	 use Date::Doomsday;
	 $doomsday = doomsday(1945);

       $Revision: 1.12 $

       Doomsday	is a concept invented by John Horton Conway to make it easier
       to figure out what day of the week particular events occur in a given

	   $doomsday = doomsday( 1945 );

       Returns the day of the week (in the range 0..6) of doomsday in the
       particular year given. If no year is specified, the current year	is

       Rich Bowen (

       Doomsday	is a simple way	to find	out what day of	the week any event
       occurs, in any year. It was invented by Dr John Horton Conway.

       In conjunction with Date::DayOfWeek, it can calculate the day of	the
       week for	any date since the beginning of	the Gregorian calendar.

       The concept of doomsday is simple: If you know this special day (called
       "doomsday") for a given year, you can figure out	the day	of the week
       for any other day that year by a	few simple calculations	that you can
       do in your head,	thus:

       The last	day of February	is doomsday. That's the	28th most years, and
       the 29th	in leap	years.

       The Nth day of the Nth month is doomsday, for even values of N. That
       is, 4/4 (April 4), 6/6, 8/8, 10/10, and 12/12, are all doomsdays.
       (That is, if doomsday is	Wednesday, as it is in 2001, then October 10
       will also be a Wednesday.)

       For odd months, after March, the	following mnemonic will	help you
       remember: "I work from 9-5 at the 7-11."	(For those of you not living
       in the USA, you might like to know that 7-11 is the name	of a chain of
       stores.)	What this means	is that	9/5 (September 5) and 5/9 (May 9) are
       both doomsday. Likewise,	7/11 and 11/7 are doomsday.

       The 0th day of march is always doomsday.

       The last	day of January is doomsday in most years, and the day after
       tha last	day of January (think January 32nd) is doomsday	in leap	years.

       So, if you know the above, and you want to figure out what day of the
       week a particular day is, you do	something like the following:

       When is Christmas in 2001? Doomsday in 2001 is Wednesday. So December
       12 is Wednesday.	Count forward 2	week, and find that December 26	is a
       Wednesday. So Christmas (December 25) is	a Tuesday.

       For more	information about the origins and mathematics surrounding
       doomsday, see the following web sites:

perl v5.32.1			  2003-02-02		     Date::Doomsday(3)


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