March 14, or Pi Day (get it? 3/14!), is the annual salute to our favorite irrational number, and 2015 means the squiggly Greek letter's special day is especially geek-tastic: For the first time in a century, you can take it out five places.
You can hit 10 digits when you add the time to reach 3.141592653.
Nerds may rejoice twice that day, but they will be quick to note that 10 places is but a tiny humble pi. The number goes into infinity, and that's probably why we love it.
The Guinness record of memorization stands at 67,890 digits set in 2005 by a Chinese student who took more than 24 hours to recite them. For computers, the record keeps getting topped, with the latest claim at 15 trillion decimal places set Feb. 9. MIT has announced it will let students know if they've been admitted on Pi Day.
There are celebrations around the Tampa Bay area Saturday, but before heading out to throw some pies at MOSI's Mess Fest, does anybody really know what pi is or how to use it or what that most famous of calculations — PiR² — really means?
There are other math principles that are easier to understand, but this Greek letter has a beauty to it that seems to capture the imagination and even pop culture fame.
No matter how big or small a circle is, if you calculate the distance around it, divided by the distance across it, you will get pi.
When people want to measure ripples emanating from a central point, they use pi.
It appears that the principle of pi was used to build the Great Pyramid of Giza and it shows itself in the Old Testament in the measure of King Solomon's temple.
It's used in math, naturally, but also physics, engineering and even boosts the search for planets outside our solar system. (A short aside for geek talk: Since the volume of a planet is a percentage of pi times the radius, scientists can use the number to figure out if a planet is mostly gas like Jupiter or rocky like Mars.)
In pop culture, Pi pops up regularly on The Simpsons and on the T-shirts of teenagers ("Pi R squared? No! Pie R round! Cornbread R square"). The fashion house Givenchy named a cologne for men called pi that is "like the numeral … undefinable, mysterious, and endlessly fascinating."
In the film Life of Pi and novel by Yann Martel there are numerous references to the number's universality, its continuity, its perfection — arriving at the same result, regardless of the circular object tested, allows religion, mathematics and the symbolic themes of the story to merge.
Pi is irrational and it goes on forever, like so much in life.