# Pi Day and doomsdays

Today is Pi Day!

Pi (π) is the ratio of the circumference of a circle to its diameter. It is an irrational number but often, its decimal approximation of 3.14 is used. Since 1988, 3/14 or March 24 is celebrated as Pi Day. In November 2019, UNESCO’s 40th General Conference designated Pi Day as the International Day of Mathematics.

While various activities are held by Math enthusiasts in schools, colleges, and universities world-wide to commemorate this day, we are also reminded that Pi Day is also a Doomsday.  Doomsdays are easy to remember dates which fall on a certain day each year.

Since Pi Day 2024 falls on a Thursday, we can identify the Thursdays in every month.

For even-numbered months, the following are Thursdays:

April 4 (4/4)

June 6 (6/6)

August 8 (8/8)

October 10 (10/10)

December (12/12)

Adding or subtracting multiples of 7 to these dates will give you the other Thursdays in that month. For example, this year, October 3, 17, 24 and 31 are Thursdays. Also, December 26 is a Thursday, so Christmas Day is a Wednesday.

These dates also fall on Thursdays this year:

May 9 (5/9)

July 11 (7/11)

September 5 (9/5)

November 7 (11/7)

So, for the odd-numbered months, we just have to imagine a friend working at 7-11 from 9 AM to 5 PM.

We also know that the last day of February was a Thursday. Since 2024 is a leap year, February 1 was also a Thursday and so was January 4.