Eve Stenson, student of plasma physics and the world at large

I confess, I’m a fan of $\pi$ , the transcendental and irrational number that is the ratio of a circle’s circumference to its diameter and when written out in base 10 starts 3.14159 . . . Somewhat amusingly, I’m honestly not sure if this is confessing that I’m too much of a nerd/geek or not enough of one; we’ll get to that later, though.

I’m also a fan of pie, the dessert.

So is my cat. That is, she is a fan of pies, especially those with meringue on top. I don’t know how she feels about the number pi.

Last but not least, I’m a fan of puns and word play in general. Thus, it seems clear that I should be pulling out all the stops when when it comes to celebrating Pi Day (March 14th), especially this year (2015). As you probably already know, the best way to celebrate Pi Day is with pie.

So what’s the problem? It’s been two and a half years since I was in the habit as writing dates as month/day/year. Living in Germany, I write today’s date as 14.03.15. Furthermore, Germany doesn’t have pie, the dessert, either. Sure, there are cakes and tortes and other baked desserts aplenty, but pie — with its perfectly flaky crust containing the sweet or savory filling of your choice — is not among them. Of course, the lack of local pie-baking doesn’t keep one from baking one’s own pies (once one imports some pie plates). But the date thing is kind of an issue.

In fact, the vast majority people around the world abbreviate dates with the month in the middle. According to the Wikipedia page on the topic, there are only three countries that exclusively use MDY (month/day/year): the U.S.A., Belize, and the Federated States of Micronesia. Three others (Canada, Kenya, and the Philippines) use both MDY and DMY.

Sadly, because there are only 12 months in the Gregorian calendar, Pi Day doesn’t come at all in most of the world. That is, if you write your dates as day/month, there is no 3/14 during the year. The same is true of Mole Day, which celebrates Avogadro’s number (approximately 6.02 $\times$ 10 $^{23}$ and is traditionally celebrated on October 23rd at 6:02 — in American chemistry circles, anyway.

If we ignore the position of the separator, those who write the day before the month could consider celebrating on 31.4 . . . if only April weren’t limited to 30 days. The 22nd of July, however, isn’t a bad substitute as Pi Approximation Day (since 22 divided by 7 equals $3.\overline{142857}$ , which rounds to 3.14) — especially if your convention uses the slash as a separator, rather than the period. Of course, this has the opposite problem that Pi Day does, in that it only works for day/month folks and not month/day folks.

There are other fun geeky holidays that don’t have this difficulty. Obviously, if one is celebrating the anniversary of an event (e.g., the birthday of Darwin or Newton, or the day Yuri Gargin became the first human being in outer space), how one writes the date is immaterial.

These lose some of the playfulness that comes from the numbers of the holiday’s date being part of the equation (pun intended). Two types of date-based holidays that don’t have that problem are Square Root Days (on which the month and day are equal and the year is their square) and Pythagorean Triple Days (on which month $^2$ + day $^2$ = year $^2$ ). The 5 December 2013 occurrence of the latter even got press in the L.A. Times, complete with the headline, “Some squares sum squares to celebrate Pythagoras”. Unfortunately, neither Square Root Days or Pythagorean Triple Days are particularly frequent.

Besides, there’s something special about $\pi$ — besides having a tasty dessert as a homophone. Obviously, it has a long and illustrious history in mathematics. If you also like memorization games, racking up digits of $\pi$ can be an amusing alternative (or addition) to U.S. Presidents or poetry. I knew a modest 120 digits when I did my first NASA internship, where I learned that my mentor had me beat, with something like 200 under his belt. (The world record at the time was more than 42,000; today, it is 67,890.) Significantly, $\pi$ is often the first irrational number one learns. As a result, finding it attractive and interesting could be something of a stand-in — to oneself and/or others — of an interest in mathematics and related topics.

Not everyone is a $\pi$ fan, though, even among math and/or number aficionados. There are those who consider $\pi$ passe or unsophisticated, instead preferring the number e ( $\approx$ 2.718281828459…) or the Golden Ratio $\phi (\approx$ 1.6180339887…). There is also the “Pi is Wrong!” movement, arguing that it would be more elegant to use $\tau \equiv$ 2 $\pi$ ( $\approx$ 6.283185…) as the circle constant. There are some good arguments for this (as well as an amusing parable), though the counter-arguments aren’t bad, either.

In the end, I am OK with continuing to have a soft spot in my heart for $\pi$ , even though it had been years since I tried to recall more than a few dozen digits and even though today is 14.03 around here. Although I didn’t think of it enough in advance to throw a big party, that can be a goal for Pi Approximation Day. The popular celebration of a mathematical constant is something worth importing — along with the dessert that goes with it.