That’s right! Today is the day that we celebrate the mathematical constant π (Pi) – 3.141592653589793232384626433…
But why is today Pi Day? Because… if you write the date in the MM/DD format, today is 03/14 and 3.14 are the first three digits of the irrational number that is the ratio of a circles circumference to its diameter. That is: π. But things are even better for π day this year, because in the MM/DD/YY format, this year is 03/14/15, which is π to 5 significant figures: 3.1415. If you want to be even more meticulous, wait until 9.26 (am or pm) and 54 seconds (if rounding up) to get an even bigger dose of π. At this instant the date and time will be: 3/14/15, 9:26:54, which is π to 10 significant figures: 3.141592654! This is as good as mathematical dates can get!
But wait there’s more! Today is not the only day that we can celebrate π in the calendar year, because in just 130 days time it will be π approximation day, or the 22/7 (DD/MM), which as a fraction is a common approximation of this irrational number π.
This post was written by Brenan Dew, Astronomy Guide at MAAS – Sydney Observatory