Doomsday: Links
Links to resources on the Web for additional information about the Doomsday Algorithm
Added 1997-08-29, Updated 2012-02-29
The following web sites are about or include descriptions of Dr. Conway's Doomsday algorithm.
Doomsday Rule, by S. W. Graham, includes substantial explanations, plenty o' exercises, and examples; also available in PDF format.
Simon Cassidy comments on the "Hand" in the context of the Dee-Cecil calendar.
C.07.2 Can I calculate the date of Easter? explains Conway's algorithm for Easter, and gives another explanation of his Doomsday algorithm; includes the remark "Note to non-US readers: 'Seven-Eleven' is the name of a ubiquitous chain of convenience stores." Reader Richard Ezell wrote to me in 2004 to report that this explanation may not really be necessary, as he had seen four 7-11 stores in a seven block stretch in Bangkok, Thailand.
AST 309-TIME; What is the day of the week, given any date? contains notes by William H. Jefferys for a school course on time, with another explanation of the Doomsday algorithm (examples are from 1997).
The Doomsday Rule for Fortnights, by Jim Blowers, gives calculations for Doomsday based on 14-day periods.
Kate Larson's Mathematical poem to calculate the "day of the week" for any day of any year is a beautiful, whimsical poem, attributed to Dr. Conway, which describes the algorithm completely, including both Gregorian and Julian century adjustments. (Note: link goes to archive.org, as the original has dropped off the Web.)
The Doomsday Algorithm, by Mike Husband, is a Powerpoint presentation. (Note: link goes to archive.org, as the original has dropped off the Web.)
Any Day of the Week Using the Doomsday Rule, by Paul J. Weiss, is a C++ implementation with downloadable code.
For more information about Dr. Conway, see:
Not Just Fun and Games April 1999 Scientific American profile of John H. Conway. (Note: this article is now available online only if you purchase the digital edition.)
Charles Seife's Mathemagician -- an amusing article about John Horton Conway.
John Conway's Game of Life by Stephen Stuart -- an interactive version that you can play via your web browser.
For links to other calendar sites, see my Calendar Links page.
Knot a Braid of Links
The Doomsday Algorithm was "latest link in the braid" for the week of
April 6-12, 1999.
"This page will teach you a simple algorithm to calculate mentally the day of the week corresponding to any given date. Give it a try, it's quite rewarding! The page features clear instructions, examples, and mnemonic tricks."
KaBoL is a "cool math site of the week" service to the mathematics community provided by the Canadian Mathematical Society.
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