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Rudy Limeback

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Added 1994-02-22, Updated 2019-02-28 with examples for 2019The Doomsday Algorithm is presented in the following sections.Have fun!To use the Doomsday Algorithm in any year, we first need to know the Doomsday for that year.Doomsday is February 28 or 29. In other words, Doomsday is always the last day of February. In normal years, Doomsday is February 28, and in leap years, Doomsday is February 29.In 2019, which is not a leap year, the last day of February is Thursday the 28th.Once we know Doomsday, it's pretty easy to get the day of the week for any day in February. For February, it's always the 28th in normal years, and the 29th in leap years.Example: what is this year's Valentine's Day, February 14th? Thursday.Example: what is this year's Groundhog day, February 2nd? Saturday the 9th, which is the same day of the week as Okay, the last day of February is Doomsday. There are actually 52 (or 53) other days which are all on the same day of the week as "the" Doomsday at the Each month has a special day which we remember, because it is on the same day of the week as the Doomsday which is at the end of February. and that all the other Doomsdays within the year are on the same day of the week. April 4th is a Doomsday August 8th is a Doomsday October 10th is a Doomsday December 12th is a Doomsday Example: what is this year's Christmas Day, December 25th? like Christmas is always the day before Doomsday. for the 9th month, Doomsday is the 5th for the 5th month, Doomsday is the 9th for the 7th month, Doomsday is the 11th for the 11th month, Doomsday is the 7th Example: what day is this year's July 4th? Thursday, so the Doomsday for July (7th month) is the 11th, also a July 4th is always Doomsday. Example: what is this year's Labour Day, the first Monday of September? Doomsday, the last day of February, is often also called the "0th" of March. exactly one week after the last day of February, no matter whether it's the 28th or 29th, is also Doomsday. Example: what day is this year's St. Patrick's Day, March 17th? Pi Day is always Doomsday. Example: what is this year's New Year's Day (January 1st)? If Doomsday is Doomsday advances by one day each year because 365 divided by 7 leaves 1 remainder. Doomsday advances two days each leap year, and we'll come back to more on that in a moment. 2018, when Doomsday was Example: what day of the week was New Year's Eve, Now, Doomsday 2018 was (Notice also that 1900 is not a leap year, so Doomsday 1900 is February 28th.) November 27th 1982 was Saturday; that was the day the Doomsday Algorithm was featured on Quirks and Quarks August(8) 8th is Doomsday December(12) 12th is Doomsday Each normal year advances Doomsday by one day. Each leap year advances Doomsday by two days. Example: what day of the week is Canada's 300th birthday, July 1st, 2167? recorded as so many days "on" (i.e. to be added) or "off" (subtracted) from that Doomsday. In a leap year, we must subtract 1 from the Doomsday Difference for January and February dates: Valentine's Day, February 14, is always "1 off" Doomsday in leap years, when Doomsday is February 29th; in ordinary years, the Doomsday Difference for Valentine's Day is 0 Groundhog Day, February 2, is only "1 on" Doomsday in leap years, when Doomsday is February 29th; in ordinary years, the Doomsday Difference for Groundhog Day is "2 on" New Year's Day, January 1, is always "3 off" Doomsday in leap years, when Doomsday is the 4th of January; in ordinary years, the Doomsday Difference for New Year's Day is "2 off" Here, in his own description, is how Dr. Conway would calculate the day of the week for Pearl Harbor Day, December 7th, 1941. I've been teaching Doomsday Rule for about fifteen years because I can show students the first day of class what my exam questions Doomsday is a good way to get them there on the first day. And of course March 14th is always a Doomsday. What Day Is Doomsday? for Doomsday based on 14-day periods. Return to topOkay, the last day of February is Doomsday. There are actually 52 (or 53) other days which are all on the same day of the week as "the" Doomsday at the end of February, but there's a special one each month which we will now learn.Each month has a special day which we remember, because it is on the same day of the week as the Doomsday which is at the end of February. and that all the other Doomsdays within the year are on the same day of the week.Let's begin with the even months. Now we can simply work our way around any even month based on its Doomsday.Example: what is this year's Christmas Day, December 25th? like Christmas is always the day before Doomsday.Example: what is this year's Halloween, October 31st? like Halloween is always Doomsday.Example: what is this year's Canadian Thanksgiving Day, the second Monday in October? using the Doomsday for that month.Example: what day is this year's July 4th? Thursday, so the Doomsday for July (7th month) is the 11th, also a July 4th is always Doomsday. Example: what is this year's Labour Day, the first Monday of September? Doomsday, the last day of February, is often also called the "0th" of March. exactly one week after the last day of February, no matter whether it's the 28th or 29th, is also Doomsday.Example: what day is this year's St. Patrick's Day, March 17th? Pi Day is always Doomsday.Finally, we have to be able to do January. If Doomsday is Doomsday advances by one day each year because 365 divided by 7 leaves 1 remainder. Doomsday advances two days each leap year, and we'll come back to more on that in a moment.Let's work a couple of examples for last year, 2018, when Doomsday was Now, Doomsday 2018 was (Notice also that 1900 is not a leap year, so Doomsday 1900 is February 28th.) November 27th 1982 was Saturday; that was the day the Doomsday Algorithm was featured on Quirks and Quarks For some of us, that's a big IF; it reminds me of a comment someone made when first shown the entire Doomsday Algorithm:Find the day of the week for any year in history in your head? August(8) 8th is Doomsday December(12) 12th is Doomsday Tuesday as the Doomsday for the 2000's.Let's work through a couple of examples.Example: what day of the week is May 29, 2017? May 29th, 2017 is Monday.Example: what day of the week is July 20, 2069? Remember the rule for determining a leap year:Each normal year advances Doomsday by one day. Each leap year advances Doomsday by two days. same Doomsday, plus or minus 400 years.Example: what day of the week is Canada's 300th birthday, July 1st, 2167? July(7) 11th is a Saturday, so July 1st, 2167, is Wednesday.Return to topDr. Conway now teaches the Doomsday algorithm, complete with Century adjustment, using a very simple visual aid—your hand.1 -- Doomsday Difference recorded as so many days "on" (i.e. to be added) or "off" (subtracted) from that Doomsday. Recall a couple of the examples we've covered:July 4th is always Doomsday, i.e. the Doomsday Difference is 0Christmas, December 25th, is always "1 off" DoomsdayBe careful with the Doomsday Difference for dates in January and February. In a leap year, we must subtract 1 from the Doomsday Difference for January and February dates:Valentine's Day, February 14, is always "1 off" Doomsday in leap years, when Doomsday is February 29th; in ordinary years, the Doomsday Difference for Valentine's Day is 0Groundhog Day, February 2, is only "1 on" Doomsday in leap years, when Doomsday is February 29th; in ordinary years, the Doomsday Difference for Groundhog Day is "2 on"New Year's Day, January 1, is always "3 off" Doomsday in leap years, when Doomsday is the 4th of January; in ordinary years, the Doomsday Difference for New Year's Day is "2 off"Here, in his own description, is how Dr. Conway would calculate the day of the week for Pearl Harbor Day, December 7th, 1941.The various numbers to be attached to the hand are (reading from the thumb):Don't start adding these up until you've formed them all, and then proceed as far as possible by cancelling first 14s, then 7s. To make sure we haven't forgotten them, let's say: " 2, Wed, 3, 5, 1 "(touching the appropriate digits as we do so), and then cancel that 2+5=7 (and folding down the thumb and ring finger) to get "Wed, 3 and 1 " = Wed + 4 = SunI also advise use of my mnemonic names for weekdays, namely: NUNday, ONEday, TWOSday, tWEBLESday, FOURSday, FIVEday, SIXurday, SE'ENdaywhich can be pronounced so that they both sound like numbers and weekdays, and so help you do the addition, for example " TREBLES, 3 and 1 = SEVENday " (Sunday)in the above case.The nice part about Dr. Conway's Hand is that we do the calculations in the same order we usually say the date -- month/day, I've been teaching Doomsday Rule for about fifteen years because I can show students the first day of class what my exam questions Doomsday is a good way to get them there on the first day. And of course March 14th is always a Doomsday. What Day Is Doomsday? for Doomsday based on 14-day periods. I've been teaching Doomsday Rule for about fifteen years because I can show students the first day of class what my exam questions Doomsday is a good way to get them there on the first day. And of course March 14th is always a Doomsday. What Day Is Doomsday? for Doomsday based on 14-day periods. I've been teaching Doomsday Rule for about fifteen years because I can show students the first day of class what my exam questions If Thanksgiving Thursday is November 27 in a Leap Year, what is the day of the week of Feb. 28 that year?Students can think they have mastered the rule and still not answer the question. Doomsday is a good way to get them there on the first day.Students invariable ask why the name. And of course March 14th is always a Doomsday.Note: Roman also included a January trick by his son Sandy Weil which is mentioned in Odd Months.Return to topThe following web sites are about or include descriptions of Dr. Conway's Doomsday algorithm.Doomsday Rule — the Wikipedia entry; very comprehensive.What Day Is Doomsday?

As said here by Rudy Limeback