# Countdown to Pi Day

If you travel in certain circles, which you likely do, you’ve probably heard that Pi Day this year is special. This year it aligns not just with 3.14 but with 3.1415, a feat of the Gregorian calendar that will not happen again for a century. At which point most of us will not be around. Which was not intended to be a pun.

As we countdown to the big day, here’s a random assortment of things to know about our friend pi:

• pi is the ratio of a circle’s circumference to its diameter.

• No matter the size of the circle, pi remains the same. In fact, Brady Haran over at Numberphile shows us how pi can be used to calculate the circumference of the observable universe.

• MIT mails out acceptances letters on Pi Day and prepares everyone weeks before with a fun video. This year’s involves drones – watch it here.

• You can run in a Pi Day race everywhere from Columbus to Seattle to Chicago to New York to one of my favorite small towns — Dexter, Michigan. Some are 5Ks, but many are 3.14 miles.

• If you write 3.14 on a piece of paper, hold it up to a mirror, and squint, it kind of spells PIE.

• YouTube has A LOT of Pi Day videos.

• U.S. House Resolution 224 declared March 14 National Pi Day in 2009. If only it had been Resolution 314. 314 is the Notch Fairness Act of 2015.

• The constant was assigned the Greek letter pi back in the 1700s.

• Ancient Babylonians and Egyptians had approximations for pi of 3.125 and 3.1605, respectively.

• Then Archimedes came along and developed the polygonal approach to approximating pi, one of his major contributions to mathematics. The more sides a polygon has, the closer it approximates a circle — try it out in this NOVA interactive.

• pi is not capitalized, even at the beginning of a sentence. Unless it is a proper name – like the man on the boat with the tiger.

This Saturday we can all advocate for pi. Remind everyone what the day is really about — which is, of course, more than just a chance to eat flaky pastry with a fruity filling and make jokes about how pies are not square. It is a day to thank this humble yet irrational workhorse of mathematics for helping us to consistently calculate so many things.

Whatever your preference – apple, blueberry, lemon meringue, chicken pot – enjoy the day.