This year has the perfect π day: March 14, at 9:26:53 (and a tad). Also written as 3/14/15;9:26:53, which is incredibly close to the value of π: 3.14159265358979323…..
Purists will object, of course, to the hour: 9. They will insist that time should be written 09:26:53. They will also object to 2015 being written as ’15’.
We will ignore those people.
This date and time happens only once every hundred years. But, like the infamous Y2K “millennium year” of 2000 (the new millennium really began in 2001), we’ll have another chance next year, on March 14, 2016: 3/14/16
There are lesser π days, one every year on March 14, at 1:59 (a.m., of course; the afternoon time would be 13:15).
3.1416 is a really good approximation to π. The difference between that value and π is one part in slightly over 136,000. This is good enough for engineering work, and certainly good enough for government work. Unless, of course, you’re sending space probes to distant planets, in which case you’d better be using all the digits your computer can handle.
For a number innately bound up with circles, π shows up in many mathematical contexts, in physics, cosmology, and higher mathematics. Thre are hundreds of formulas – mathematical series – for computing π, but since it has already been calculated to billions of digits, there’s really not much use for those series (except perhaps to check your arithmetic).
Here’s a website devoted to π.
Here’s theultimate π image