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Pi Day 2015: a match-up that occurs once every 100 years



Saturday March 14 is national Pi Day.

Pi is the mathematical constant (π). The value of pi is 3.141592653 (that’s just the first ten digits). The approximate value is 3.14.

March 14 is Pi Day because in countries that write month/day it is 3/14, which corresponds to the first three digits of pi.

But March 14, 2015 is extra special because the 10-digit correspondence only occurs once every 100 years. This year, if you write the date as month/day/year then it is 3/14/15, which is the first five digits of pi (3.1415). In a hundred years time - in 2115 - the date will also be 3/14/15. 

At 9:26:53 in the morning, and in the evening, the date and time will correspond to the first 10 digits of pi (3.1492653). This, according to Jeffrey S. Rosenthal, professor of statistics at the University of Toronto, Canada, is called Pi Instant – the very instant at which the date and time include all ten digits of pi.

July 22 will be celebrated as Pi Approximation Day because it is 22/7 in countries that write day/month, which is 22 divided by 7, which corresponds to the approximate value of pi (3.14).

Why do mathematicians love pi? Pi is an irrational number. It is the ratio of any circle’s circumference to its diameter in Euclidean space (or the ratio of a circle’s area to the square of its radius). The actual value of pi never ends and never repeats.

π = 3.141592653589793238462643383279502884197…


Pi Day was first celebrated in 1988 at the San Francisco Exploratorium. Museum staff and the general public celebrated by walking around a circular space and then eating fruit pies. Generally it is celebrated with pi-themed activities (such as eating pies or eating food that start with pi – such as pineapple, pizza and pine nuts).


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