Every year on March, 14 people all over the world celebrate one of the most unusual holiday ever - International Pi Day, the day of mathematical constant Pi which shows the ratio of a circle's circumference to its diameter. It has an approximate value of 3.14159, and that explains why the celebration date is March, 14 (3/14). Here in this article we will learn about the history of such an interesting day, and about why other constants haven't become as popular.

First Pi Day ever was celebrated in 1988 in San-Francisco Exploratorium scientific museum. The day itself was invented a year before by Larry Shaw, San-Francisco physicist: he noticed that American date format (where a month goes before a day) notation of March, 14 (3/14) looks like first digits of Pi constant.

Since Pi is irrational, it has infinite length, so there are really lots of digits. Most of the Pi days are limited to just three digits, but year 2015 is going to be special: not only the date would be 3/14/15, but there will be a really epic moment at 9:26:53, when 10 digits will be covered at once!

But why has Pi day become so popular, when there are a lot of various physical and mathematical constants? For example, there's "e" which is also irrational and has a value of 2.71828 and so on - and February, 7 would be a good day to celebrate international E Day. There are also a lot of constants every physicist should know, so there could be International Acceleration Of Gravity On Earth Day (September, 8) or even Gravitational Constant Day (June, 6 - although that one could be a bit cheating since gravitational constant actually starts with a lot of zeroes).

One of the reasons the Pi has become so popular is because of its connection with circle - one of the most ancient, well-known and even mystical geometrical figures. Pi is known since ancient times: its first mentions appear in Greek mathematical studies. There's even a legend saying that Babylon tower has fallen because of low Pi precision at ancient times - the tower height multiplied by error in calculating circumference caused the tower to collapse.

You can't say the same thing about "e" or "g". But there's also a reason that is way more practical: Pi is about circles, and so as pies. Pi even sound similar to "pie". And what can be a better way to celebrate a holiday than a good holiday pie?