Leap Day, Feb 29th is Doomsday

Feb 29th is indeed doomsday.  In fact, every Leap Day of every Leap Year is doomsday.  At least it’s doomsday according to the Doomsday Rule or the Doomsday algorithm.

There is an algorithm that allows the user to figure out on what week day was Christmas 1000 years ago.  That algorithm is called the Doomsday algorithm.  The formula has two anchor days.  Anchor days are jumping off points for the doomsday calculation.  There is one anchor day for the century and one for the actual year.  The anchor day for the actual year is also called a doomsday.  The anchor day for our century is Tuesday.  The anchor day for 2012 is Wednesday.  If you check, you will see that Feb 29th 2012 is indeed on a Wednesday.

But wait there is more.  We also know what weekday 4/4, 6/6, 8/8, 10/10 and 12/12 are on.  They are all on doomsdays of their own.  So April 4 2012 is on the same week day as December 12 2012.  Which is to say, Wednesday.

For odd months, the rules are different but suffice it to say that July 4th 2012 is also on a doomsday–Wednesday.

For most normal people, doomsday calculations are more math than you would willingly want to shake a stick at but let’s take a look anyway.

Let us take a look at a method that Wikipedia calls the Odd 11 method.

The formula is : 

( Y + Y/4) mod 7.

Y is the last two digits of the year.   Mod is short for modulus.  Modulus means find the remainder.

Now let’s check the formula out for 2012.

(12 + 12/4) = 15   15 mod 7 =1.

Now the anchor day for the century we will just get from a chart.  It’s Tuesday.  Add one day from our result to get the anchor day for 2012 and you get Wednesday. 

Let’s day you want to use the litle doomsday to calculate the day of the week of the big Doomsday 21 December 2012.

Note that the little doomsday for December is 12/12/12.   That day then, falls on Wednesday.  One more week and we have that 12/19/12 is also on a Wednesday.  Two more days and the end of the world falls on Bad Friday, 21 December 2012.

How to Calculate doomsday

Image via Wikipedia