Tomorrow, March 14th, is Pi Day. No, that’s not a typo. It is Pi day, as in 3.14159… you get the idea. The first Pi Day celebration was held at the San Francisco Exploratorium in 1988. That means tomorrow is the 20th anniversary of Pi Day.

What is pi anyway? I’m sure you remember it from math in some formula you memorized, but do you really know what it is? Pi represents the relationship between a circle's **diameter** (its width) and its **circumference** (the distance around the circle). Pi is always the same number, no matter the circle you use to compute it. In school we generally approximate pi to 3.14 in school, but professionals often use more decimal places and extend the number to 3.14159.

One activity I loved doing with students was to ask them to bring in a can and lid that would soon be recycled. I always brought in a few extras so that there would be a variety of sizes. Each student was given a lid and directed to measure the diameter and circumference. Students then divided the circumference by the diameter. We recorded the results on the overhead and discussed them. Most were amazed to find that the results were nearly the same, allowing for some margin of error in measurement. This is a quick and fun and provides a meaningful way to introduce the concept of pi.

What will you be doing for Pi Day? I hope you’ll be celebrating in some small way. Perhaps you could make a pi necklace. If you’re looking for ideas, visit the Exploratorium pi site. Since tomorrow will be poetry Friday, I just may write some pi poems.