From the wheels that get you from Point A to Point B, to the GPS system that helps you find your way, there is a single number that makes these and countless other innovations possible.

Pi, an irrational number typically approximated as 3.14159, has proved itself as both a captivator of the imagination and an irreplaceably practical part of everyday life.

Last Saturday saw the observance of Super Pi Day, a once-in-a-century event on which the date (3/14/15) most closely corresponds to the mathematical representation of pi. Attendees at the Tucson Festival of Books on the University of Arizona campus celebrated the occasion with the Science of Pi, a brand-new addition to Science City that featured a number of activities and demonstrations designed to showcase the importance of the vaunted number.

At the Science of Pi tent, visitors used pi to design their own bouncy balls, created colorful visual representations of pi, and participated in a Buffon's Needle experiment. In the experiment, participants tossed toothpicks across a board with parallel lines. At the end of the day, the ratio of the number of sticks thrown to the number of sticks that crossed the lines was approximately 3.14, or pi.

Science of Pi volunteers also hosted a pi digit recitation contest — which took place at 3:14 p.m., of course. Austin Troike, the contest winner, accurately recited 171 digits of pi from memory.

Science City's Science Café lecture series featured Rebecca Klemm, a statistician and renowned STEM educator known popularly as the "Numbers Lady." Her talk, "The Intriguing Story of Pi," attracted audience members young and old as she explained the long history and countless uses of pi alongside a giant stuffed pi doll. On campuses elsewhere, five-kilometer (3.1-mile) races were part of the fun, some of them billed as "The Pi Mile," starting at 9:26 a.m. (for 3.1415926) and serving pie afterward.

What is it about pi that calls for such a celebration? Put simply, pi is one of the oldest and most widely used mathematical constants known to mankind.

Nearly 4,000 years ago, ancient Babylonians and Egyptians made the observation that the ratio of a circle's circumference to its diameter (C/d) was the same constant for every circle. While early estimations of this constant were inaccurate, the Babylonians and Egyptians were among the first to show that pi could be used to calculate the area of a circle.

More accurate calculations of pi came from the famous Greek philosopher Archimedes in the 200s B.C. and the Chinese mathematician Zu Chongzhi in the fifth century. Mathematicians worldwide continued to delve more deeply into the meaning of pi for the next several centuries.

In the early 1700s, mathematicians William Jones and Leonhard Euler popularized the use of the Greek letter to represent the mysterious constant. In 1767, mathematician Johann Heinrich Lambert was the first to realize that pi was irrational, meaning that it is not a terminating or repeating sequence of digits.

Not only did Lambert help to illuminate the nature of pi as we know it today, he also ensured that pi digit memorizers would always have their work cut out for them.

However, modern applications of pi extend far beyond Pi Day contests and calculating the area of circles in middle-school math class. Pi is fundamental to every science and engineering discipline in existence today.

Mechanical engineers use pi to design and build aircraft, cars and other heavy machinery. Pi is used in signal processing, which provides the basis for radio, telephones and TV. Statisticians use pi to make sense of large data sets of all kinds. And computer engineers frequently employ pi to write the programs behind the digital devices we all know and love.

Amazingly, pi also is readily found in the natural world. Pi can be used to accurately describe the geometry of the DNA double helix, found in every living being on the planet. Pi has helped astronomers accurately determine the shape of — and distances between — stars, planets and other celestial bodies. The behavior of naturally occurring waves, such as those of light or sound, can be predicted using pi. Using pi to study the shape of the eye has been invaluable in the fields of optometry and ophthalmology. Finally, pi is found in the shapes of rivers and the way they wind across a landscape.

The discovery of pi represents a monumental achievement in human history, and this year's Super Pi Day festivities provided festival participants with the perfect way to celebrate.