# Happy Pi Day! Fun facts about our favorite irrational number

Math lovers celebrate March 14 as Pi Day, in honor of the irrational number pi.

Pi, or π, is defined as the ratio of the circumference of a circle to its diameter. Pi is an irrational number, meaning it cannot be written as a simple fraction. Instead, it can be expressed as an infinite, nonrepeating decimal (3.14159...) or approximated as the fraction 22/7.

Here are some nerdy facts about the irrational number, to impress your friends as you celebrate Pi Day (which is also Albert Einstein's birthday). [The 9 Most Massive Numbers in Existence]

1. Discovery of pi

The ancient Babylonians knew of pi's existence nearly 4,000 years ago. A Babylonian tablet from between 1900 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. The King James Bible (I Kings 7:23) gives an approximation of pi in cubits, an archaic unit of length corresponding to the length of the forearm from the elbow to the middle finger tip (estimated at about 18 inches). The Greek mathematician Archimedes (287-212 B.C.) approximated pi using the Pythagorean theorem, a geometric relationship between the length of a triangle's sides, and the area of polygons inside and outside of circles.

2. There's a pi "language"

Literary nerds invented a dialect known as Pilish, in which the numbers of letters in successive words match the digits of pi. For example, Mike Keith wrote the book "Not a Wake" (Vinculum Press , 2010) entirely in Pilish:

Now I fall, a tired suburbian in liquid under the trees,Drifting alongside forests simmering red in the twilight over Europe.

("Now" has three letters, "I" has one letter, "fall" has four letters, and so on.)

3. Memorizing pi

Number enthusiasts have memorized many digits of pi. Many people use mnemonic techniques, known as piphilology, to help them remember. Often, they use poems written in Pilish (in which the number of letters in each word corresponds to a digit of pi), such as this excerpt:

How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics.

The record for the most digits of pi memorized belongs to Chao Lu, of China, who recited pi from memory to 67,890 places in 2005, according to The Guinness World Records.

4. Pi-ramid at Giza

The publisher and writer John Taylor first proposed the idea that Egypt's Great Pyramid at Giza, built around 2589 to 2566 B.C., was designed based on pi. Taylor found that dividing the perimeter of the pyramid of its base by its height produces a number that is close to 2*pi. Other people have since made the link between the Great Pyramid and pi as well, although it may not have been intentional.

5. Computing pi

It's easy to calculate pi by measuring the circumference, or the distance around the edge of a circular or curved object, and the diameter of several circles, and computing the slope (circumference divided by diameter). Computers can get even more accurate measurements. As of December 2013, according to Numberworld.org, computers calculated pi to a record 12 trillion digits.

Think about that, as you munch on some tasty Pi Day pie! Pi Day celebrations will be held in New York at the Museum of Math andMichael Albert Gallery. In California's Bay Area, the Exploratorium is having its own Pi Day festivities.