Pi – which is written as the Greek letter for p, or π – is the ratio of the circumference of any circle to the diameter of that circle. Regardless of the circle’s size, this ratio will always equal Pi.
Babylonians and Egyptians had rough numerical approximations to the value of Pi, and later mathematicians in ancient Greece, particularly Archimedes, improved on those approximations. By the start of the 20th century, about 500 digits of Pi were known.
The most accurate value for Pi, according to Guinness World Records, is more than 62 trillion digits (62,831,853,071,796 to be precise), by University of Applied Sciences of the Grisons (Switzerland) in Chur, Switzerland, on August 19, 2021. (Guiness World Records) (Others have since computed beyond this.)
In decimal form, the value of Pi is approximately 3.14 – thus the expression that today, March 14, is Pi Day.
But Pi is an irrational number, meaning that its decimal form neither ends (like 1/4 = 0.25) nor becomes repetitive (like 1/6 = 0.166666…). (To only 18 decimal places, Pi is 3.141592653589793238.)
Hence, it is useful to have shorthand for this ratio of circumference to diameter. According to Petr Beckmann’s A History of Pi, the Greek letter π was first used for this purpose by William Jones in 1706, probably as an abbreviation of periphery, and became standard mathematical notation roughly 30 years later.
Try a brief experiment: Using a compass, draw a circle. Take one piece of string and place it on top of the circle, exactly once around. Now straighten out the string; its length is called the circumference of the circle. Measure the circumference with a ruler.
Next, measure the diameter of the circle, which is the length from any point on the circle straight through its center to another point on the opposite side.
If you divide the circumference of the circle (distance around the perimeter of the circle) by the diameter (distance across the circle through the center), you will get approximately 3.14 – no matter what size circle you drew (every circle has the same ratio of circumference to diameter).
In addition, Pi also connects the radius of a circle (half the diameter) with the area of that circle by the formula: the area is equal to Pi times the radius squared. Additionally, Pi shows up often unexpectedly in many mathematical situations.
(For example, the sum of the infinite series uses Pi (it’s a Basel problem concerning an infinite sum of inverse squares … (the series is the sum of 1/n2, as in 1/12 + 1/ 22 +1/32, etc)) that is represented as, 1 + 1/4 + 1/9 + 1/16 + 1/25 + … + 1/n2 + … is π2/6) (Scientific American) (Don’t you just love math?)
Why else is Pi important? Pi is key to accurately pointing an antenna toward a satellite. It helps figure out everything from the size of a massive cylinder needed in refinery equipment to the size of paper rolls used in printers.
Pi is also useful in determining the necessary scale of a tank that serves heating and air conditioning systems in buildings of various sizes.
NASA uses Pi on a daily basis. It’s key to calculating orbits, the positions of planets and other celestial bodies, elements of rocket propulsion, spacecraft communication and even the correct deployment of parachutes when a vehicle splashes down on Earth or lands on Mars.
Using just nine digits of Pi, scientists say it can calculate the Earth’s circumference so accurately it only errs by about a quarter of an inch (0.6 centimeters) for every 25,000 miles (about 40,000 kilometers). (WBUR, NPR)
How’s this about Pi? … Possibly the world’s best-known scientist, and one of the greatest and most influential scientists of all time, Albert Einstein was born on March 14, 1879, in Germany. Oh, and famed physicist Stephen Hawking died on March 14, 2018.
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