If you are reading this on March 14th at 1:59 p.m., then it must be Pi Day! (Pi at 5 decimal places = 3.14159 : )
What is Pi Day, you ask? Only an annual celebration of the mathematical constant π (Pi), or in its easiest understood numeric equivalent, 3.14 (which is why the 14th day of the 3rd month was chosen as Pi Day, 'natch!) Started in 1988 by physicist Larry Shaw at San Francisco's Exploratorium Museum to commemorate the importance of mathematics in our everyday lives, today's date also coincides with the birthday of that guy who came up with that other famous mathematical equation, E = mc^{2}— Albert Einstein! Princeton, NJ goes all out by celebrate both Pi Day and the life of its most famous resident with their annual Pi Day Princeton celebration.
But what is Pi? Well, it represents the ratio of a circle's circumference to its diameter, on a flat plane surface (as you can see in the following animated gif):
Pi has everyday, practical uses from the fields of architecture and engineering to helping plot air travel and calculating satellite signals for television transmissions. Pi is incredibly irrational though, as it's a nonrepeating, infinite string of numbers occurring naturally. Even with the help of super computers calculating Pi to the trillionth decimal place, scientists and mathematicians have still been unable to find a pattern or an end.
Here's some fun (and even educational) ways you can celebrate Pi Day:

From our online catalog, you can read The Joy Of Pi by David Blatner (there's also a corresponding website with lots of useful info about Pi!) Maybe a movie is more your speed? Then watch Darren Aronofsky's scienceandmathgonemad Pi, about a mathematician who is driven mad trying to solve the irrational mathematical computation. We even have the Star Trek: The Original Series episode "Wolf In The Fold", where the Enterprise’s computer tries to compute the last decimal of Pi but ends up instead sending the ships computer out of control and into an infinite loop!

Check out these Pi Daythemed pics and activities for adults and children on Pinterest, including visualizing Pi with this cool infographic.

For teachers, visit TeachPi.org for lots of great classroom lessons and activities for students of all ages.

As mentioned earlier, you can celebrate with the originators of Pi Day over at San Francisco's The Exploratorium, who will have a number of events taking place online.

And if you really want to geek out, just hop on Wikipedia and fall down a Pi wormhole of Pi and Pirelated topics.

If numbers and mathematical calculations aren't you're thing, you can still celebrate by adding an "e" to that Pi and having a slice of Pie! Check out these Pi Day "Pie" recipes, from sweet to savory and everything in between.

Finally, take a listen to these musicians interpret Pi to 31 decimal places, illustrating how music really is math and vice versa:
Use search terms like "mathematics", "geometry", and "number theory" in our online catalog for more Pirelated titles and feel free to "like" and share this post on social media with the hastag #PiDay!