For the past 30 years, the holiday has been celebrated on March 14, the day of the year that lines up with the first three digits of pi.

Meanwhile, NASA is also celebrating Pi Day in its own special manner.

Pi (Greek letter "I") is the symbol used in mathematics to represent a constant - the ratio of the circumference of a circle to its diameter - which is approximately 3.14159.

More news: Raiders to release high-price CB SmithHistorically, the first Pi Day was held at a San Francisco Science Museum in 1988 when the physicist looked at the calendar and chose to pay homage to the mathematical entity. A Babylonian tablet from between 1900 B.C. and 1680 B.C. calculates pi as 3.125, and the Rhind Mathematical Papyrus of 1650 B.C., a famous Egyptian mathematical document, lists a value of 3.1605. For those who are wondering what it is, it's Pi Day. Nowadays, Pi Day is often associated with food - perhaps pizza, or a meat pie, but in this case, a classic American apple pie with a French twist. Ansel, in his signature chef style, honoured the mathematical constant by demonstrating the pi formula using his personal Salted Caramel Apple Pie recipe.

Pi is useful in every field of science as it's used for calculations involving the volume and surface area of spheres, as well as for determining the rotations of circular objects such as wheels.

According to piday.org, Pi has been calculated to over one trillion digits beyond its decimal point.

More news: Serena Williams Loses Her First Match To Older SisterThe Pi constant was also celebrated in music and movies. It was however, William Jones, a mathematician from Wales, who first gave the Greek letter its current mathematical definition. Therefore, it is an irrational number which is less than infinity.

Pi is also a source of inspiration for competitions, where participants have to recite as many decimals of the number as possible.

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