Every year at 1:59 p.m. on March 14 the folks at San Francisco’s Exploratorium celebrate pi – it’s the constant 3.14159 …

Click here for the best Pi day infographic you’ll ever see. It would make Archimedes proud.

There’s a pi dance, pi beading, a pi channel, a pi shrine. It’s just a little out of hand — but if you love math, you’ll love pi day.

So what is pi really? A refresher for you: Pi is the infinite number you get when you calculate the ratio of a circle’s circumference to its diameter. The Babylonians, Egyptians and even the Bible mention pi several centuries before the ancient Greek Archimedes of Syracuse began promoting it — under his own number — about or around 260 B.C.

Find an in-depth history here.

Cool pi facts I happen to know or that I’ve gathered up over the years:

- Pi didn’t come out of Ancient Greece. Archimedes of Syracuse called the number that we now know as pi by a different name entirely. He renamed it after himself. He called it Archimedes’ Constant.
- William Jones of Wales (no known relation to Wikipedia founder Jimmy Wales) gave pi its current name in 1706.
- March 14 — Pi Day — is also Albert Einstein’s birthday. Cool.
- Another way to describe pi — it’s the number of times the diameter of a circle will fit around its circumference.
- No one knows how pi ends. It’s an irrational number that is apparently infinite. It just keeps going and going, with no repeating series of numbers. It’s been calculated to well over a trillion places in recent months.
- Calculating pi isn’t as cool as memorizing and reciting it. There are actually clubs that train people to do this. I once saw a Japanese student, Kiroyuki Gotu, recite pi from memory during a competition. It took him 112 hours — he recited it accurately to 42,195 places on stage at the NHK Broadcasting center in Tokyo.
- Pi is useful for another purpose. Use it to figure out your hat size. Measure your head — its circumference — divide the measurement by pi and round it off to an eighth of an inch.
- If you ever are assigned the task of estimating the height of an elephant, here’s the trick. Measure the diameter of its foot and multiply that number by two. Then multiply the result by pi.
- A number that goes on as long and apparently as randomly as pi is ripe for all kinds of weird conspiracy theories. There are entire sites dedicated to helping you find your birthday and other meaningful dates in pi. Convert pi into images, audio files and, even alphabetic sequences where you can seek out personal messages. Too funny. The Satanical signature 666 doesn’t make an appearance until position 2240. Worth noting.
- Try singing the line “pi, pi, 3.1415″ to the tune of Don McLean’s “Bye, Bye, Miss American Pie.” Some kids in CA came up with this years ago — right before the Exploratium kicked off a pi day in the spring of 1999. The kids wrote an entire song to the tune and they dedicated it to the day their “math team tied” as opposed to “the day the music died.”
- The true beauty of pi lies in its flexibility. Find it in harmonic motion theory, superstring calculations, Einstein’s gravitational field equation and more.
- Would you believe you could calculate a circle the size of the entire universe (down to a proton) using pi to just 39 places? It’s true.

And here’s to “Pi, Pi Mathmatical Pi.” It’s sung to the tune of Don McLean’s “American Pie” with rhyming lyrics to help you remember the pi digits — ie, instead of “Bye, bye Miss American Pie” the artist sings “Three, point, one, four, one, five.” Funny.

Find the real lyrics here. Video of the pi version below.

Here’s a pi song — composed by matching the numbers in the pi string to notes. It’s the sound of pi!

And I love this. Created just for Pi Day, it’s the Pi Domino Spiral. See if you are able to solve its many hidden references.

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