Pi Day celebrates date of the number that is the ratio of a circle’s circumference to its diameter.

The celebration is held annually on March 14, because 3/14 spells out the first three digits of π, or pi, which is 3.14.

2015 is the first time in a century that the date is 3/14/15, which describes the first five digits of pi, 3.1415. Mass elation peaks at 9.26:53 AM when the date and time will describe pi to 10 digits.

Originally a US-based initiative to promote mathematics to pupils – hence the American date format, 3/14 – Pi Day has in recent years transformed into a kind of nerd Christmas, commemorated all over the world by children and adults – often by eating pie.

Pi Day honors mathematician William Jones, who came up with the idea of pi in 1706.

William Jones was not the first person to realize that the circumference of a circle divided by the diameter is a number that defies easy calculation, but he was the first to denote the ratio by the symbol π, suggesting it in a book as an abbreviation of either the word periphery or perimeter.

The circle is the most elementary two-dimensional shape you can draw. You can do it with a pair of compasses or a pencil tied to a piece of string. The root of fascination with pi is the fact that the ratio of the circle’s two simplest measurable quantities – the distance around it and the distance across it – produces a number that is so complicated: its digital expansion continues for ever, churning out a sequence of digits with no apparent pattern.

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