## National Pi Day, March 14

History's Garden

March 2, 2024

Thirty-seven years ago, no one had heard of Pi Day. Then along came Larry Shaw (1939-2017), a physicist at the San Francisco Exploratorium. In 1988, three years after the death of the Exploratorium founder, the staff gathered at a retreat in Monterey, California to soul search and brainstorm. It was there that Shaw linked March 14 (3.14) with the digits of pi (3.14159...) and saw it as an opportunity to bring Exploratorium staff together for some fun, camaraderie and pie. Pi Day was born.

What started in 1988 as a small staff-only gathering was so successful that the following year it was opened to the public with lots of pi themed antics and, of course, pie. A few years after the first celebration, Larry's daughter discovered that Pi Day was also Einstein's birthday (1879), so a celebration of his life was added to the museum's Pi Day festivities.

As part of the fun, Larry created and installed the "Pi Shrine," a circular brass plaque in the center of a circular classroom constructed of circular cinderblocks. Larry would lead a parade around and through the museum with a boombox blaring the digits of pi to the music of "Pomp and Circumstance." The parade would end after circling the Pi Shrine 3.14 times while singing "Happy Birthday" to Albert Einstein.

All this revelry did not go unnoticed by the rest of the country and Pi Day celebrations popped up all over. In 2009, the U.S. House of Representatives got on the bandwagon when they passed a resolution recognizing March 14, 2009, as National Pi Day.

But what is pi and why do we care?

Pi (represented by the lower-case Greek letter π) is a number that equals approximately 3.14. It is the ratio of a circle's circumference to its diameter.

π = C (circumference) divided by D (diameter).

However, it's pretty hard to measure the circumference of a circle with a tape measure because, well, it's round. Much easier to measure the D (diameter). And here's where π becomes really useful:

C (circumference of any circle) = π times the D (diameter).

Because its definition relates to the circle, π has been used by mathematicians for centuries, and it is found in tons of trigonometry and geometry formulas. Interestingly, the pi ratio did not have a universal name until 1647, when English mathematician William Oughtred began calling it pi. And it wasn't until 1700s that the π symbol was assigned to it.

The second reason we care about pi day is because it's a great excuse to enjoy a slice or four of something yummy! Larry Shaw's first Pi Day celebration included fruit pie. Nowadays, any pie is fair game. So, start out your day with a bacon and egg breakfast pizza pie.

Then take a look at the NASA-JPL Education Office online catalog of "Pi in the Sky" math challenges (https://www.jpl.nasa.gov/edu/teach/tag/search/Pi+Day). Each lesson includes a description of the real-world science and engineering behind the problem, an illustrated handout and answer key.

After all that mental exercise, it will be time for some chicken pot pie for lunch.

In the afternoon check out the We Are Teachers website (www.weareteachers.com/pi-day-activities/) for some fun activities. Round out the day with a homemade veggie pizza pie for dinner (or if you are feeling adventurous a Cornish pasty or empanada) and a slice of hot apple pie à la mode for dessert.

For a bit more fun (and more excuses for pie!), there's Pi Approximation Day on July 22 – the fraction 22⁄7 is approximately 3.14, and Two Pi Day, also known as Tau Day, is on June 28 because tau = 2π, which is approximately 6.28 (6/28).