Space & Innovation

# What Exactly is Pi Day?

## The nerdiest holiday in the world explained.

It's Pi Day! While many of us will use this day as an excuse to indulge in some delicious berry-filled, whipped topping desserts, there's actually a mathematical and historical reason why March 14 is known as Pi Day.

Pi is the mathematical term for the irrational number 3.1415926535897932384626433832795 (to 31 decimal places). The actual number never ends.

As CNN explains, "Pi is the ratio of the circumference of a circle to its diameter. It's not equal to the ratio of any two whole numbers, so an approximation -- 22/7 -- is used in many calculations."

While it's not a number most of us encounter in our everyday work, Pi is used frequently by architects and in the construction industry. The number itself has been known for approximately 4,000 years, but didn't get its name -- from the Greek letter Pi -- until the 18th century.

March 14 began as a celebration of the number Pi 28 years ago at San Francisco's Exploratorium. A physicist who worked at the museum named Larry Shaw started celebrating the day with other museum staff members on this day in 1988. Since then, math lovers around the world have caught on to this nerdiest of holidays.

Pi Day also happens to be the birthday of the world's ultimate math nerd: Albert Einstein. Princeton, N.J., where Einstein lived for 20+ years, celebrates this day with a festival that actually takes place over five days total and includes events like an author lecture, a pie eating contest, and a surprise birthday party for Albert.