Once every century our calendar and clocks order themselves in such a way to duplicate more than just a few digits of pi (the number representing the ratio of a circle's circumference to its diameter). Using American dating format, today's date is 3-14-15 which is the first four digits (not including the 3 on the left side of the decimal), and only occurs every 100 years. If one includes the time of day, we could represent 9:26:53 which would give us another 5 digits. Since seconds can be represented with fractional parts, we could technically represent an infinite number of pi digits: 3-14-15 9:26:53.589793238462643383... I think you get the idea. We'll stop at nine digits today and be happy with that.
To celebrate, we ate three pies for supper this evening as shown in the photos below.
As I'm writing this, it occurs to me that there was one moment in history when the date and time matched pi even better than today: March 14, 1592, at 6:53:58. I guess we'll have to content ourselves with the second most significant celebration of Pi Day.
I'm also aware that some guides to the Greek language suggest pi should be pronounced "pee." When considering celebrating this important number, I'd rather trust the common modern pronunciation than spend more than a few seconds contemplating celebrating per the other pronunciation.