Today is the 30th Pi Day (Greek letter “π”). March 14 (3.14) is Pi Day, a celebration of the ratio of a circle’s circumference to its diameter — one of the most beautiful and confounding numbers in mathematics. It’s technically written as 3.14159, or 3.14 for short.

Of course this only works in the American date format, but let’s all look past that to celebrate this crazy mathematical constant together. Bonus: it’s also Einstein’s birthday!

Even if you hate math, you’ll love Pi Day. Why? Because there’s pie.

Why does “pi” deserve its own day?

Why pi? The letter π is the first letter of the Greek word “periphery” and “perimeter.” Beautiful in its simplicity, pi is the relationship between the perimeter of a circle (the circumference) and the distance across that circle (the diameter). For any circle, the principle is without exception universal — meaning it’s always the same whether it be applied to a merry-go-round, a dinner plate, or a bicycle wheel.

It’s a special number. It shows up everywhere. In chemistry, physics, math, whether you’re talking circles or cycles or anything to do with a curve, you’re going to find pi in there somewhere. Pi is irrational, which means that you can’t calculate pi by dividing an integer by any other integer. Pi never ends and it never repeats. People have to wrap their brain around that. Twenty-two over seven gives you a pretty good approximation of pi, but it’s not pi.

History of pi (π)

It’s hard to pinpoint who, exactly, first became conscious of the constant ratio between the circumference of a circle and its diameter, though human civilizations seem to have been aware of it as early as 2550 BCE. The Great Pyramid at Giza, which was built between 2550 and 2500 BC, has a perimeter of 1760 cubits (1 cubit equals about 18 inches) and a height of 280 cubits, which gives it a ratio of 1760/280, or approximately 2 times pi. Egyptologists believe these proportions were chosen for symbolic reasons, but, of course, we can never be too sure.

The earliest textual evidence of pi dates back to 1900 BCE; both the Babylonians and the Egyptians had a rough idea of the value. The Babylonians estimated pi to be about 25/8 (3.125), while the Egyptians estimated it to be about 256/81 (roughly 3.16).

One Babylonian tablet (c. 1900-1680 BCE) indicates a value of 3.125 for pi, which is a closer approximation. The Rhind Papyrus (c. 1650 BCE) gives us insight into the mathematics of ancient Egypt. The Egyptians calculated the area of a circle by a formula that gave the approximate value of 3.1605 for pi.

The Ancient Greek mathematician Archimedes of Syracuse (287-212 BCE) is largely considered to be the first to calculate an accurate estimation of the value of pi. Archimedes approximated the area of a circle by using the Pythagorean Theorem to find the areas of two regular polygons: the polygon inscribed within the circle and the polygon within which the circle was circumscribed. In this way, Archimedes didn’t calculate the exact value of pi but showed that value is between 3 1/7 and 3 10/71.

A similar approach was used by Zu Chongzhi (429-501 CE), a brilliant Chinese mathematician and astronomer, using a 12,288-sided polygon. He calculated the value of the ratio of the circumference of a circle to its diameter to be 355/113.

The famous Indian mathematician-astronomer Aryabhatta (476-550 CE) worked on the approximation for pi (π), and may have come to the conclusion that π is irrational. In the second part of the Aryabhatiyam (Ganitapaada 10), he writes in Sanskrit:

caturadhikaṃ śatamaṣṭaguṇaṃ dvāṣaṣṭistathā sahasrāṇām
ayutadvayaviṣkambhasyāsanno vṛttapariṇāhaḥ.

English translation: add four to 100, multiply by eight, and then add 62,000. By this rule, the circumference of a circle with a diameter of 20,000 can be approached.

This implies that the ratio of the circumference to the diameter is ((4 + 100) × 8 + 62000) ÷ 20000 = 62832 ÷ 20000 = 3.1416, which is accurate to five significant figures. It is speculated that Aryabhatta used the word asanna (approaching), to mean that not only is this an approximation but that the value is incommensurable (or irrational). It is quite a sophisticated insight because the irrationality of pi was proved in Europe only in 1761 by Lambert.

After Aryabhatiya was translated into Arabic (c. 820 CE), this approximation was mentioned in Al-Khwarizmi’s book on algebra (from al-Jabr, which means “completion” or “restoration”). Al-Khwarizmi used to live in Baghdad.

In the 14th century, Indian mathematician Madhavan of Sangamagramam (c. 1350 – c. 1425), the founder of the Kerala school of astronomy and mathematics, discovered what is now known as the Madhava-Leibniz series (named after German mathematician Gottfried Leibniz, who rediscovered the series in the 17th century). Madhavan subsequently calculated pi to 11 decimal places. The formula for π is referred to as Madhava–Newton series or Madhava–Leibniz series or Leibniz formula for pi or Leibnitz–Gregory–Madhava series. These further names for the various series are reflective of the names of the Western popularizers of the respective series.

Mathematicians began using the Greek letter π in the 1700s. Introduced by William Jones in 1706, use of the symbol was popularised by Leonhard Euler, who adopted it in 1737.

How far have we calculated pi now?

Pi memorisation is difficult – and this is why people do it –since there is no pattern in the digits. You need to invent your own methods to remember them.

As per the latest Guinness World Records, the most decimal places of pi memorised is 70,000, and was achieved by a 21-year old Indian student named Rajveer Meena at the VIT University, Vellore, India, on March 21, 2015, beating a Chinese man named Lu Chao (67,890), who had held the record for 10 years. Rajveer wore a blindfold throughout the entire recall, which took nearly 10 hours.

Suresh Kumar Sharma, a 21-year-old former vegetable vendor from Jaipur, India, is the current record holder on the Pi World Ranking List when it comes to reciting the digits of pi. In October 2015, he recited 70,030 numbers in 17 hours. The Guinness World Records, however, says the top pi reciter is Rajveer Meena who reeled off 70,000 digits in just 10 hours in 2015 while blindfolded.

As NPR reported, Akira Haraguchi of Japan claims he is the unofficial record-holder for reciting digits of pi. In 2006, Haraguchi reportedly recited 111,700 digits in 16 hours, 30 minutes, but his public recitation hasn’t been formally recognized by Guinness World Records.

The current record for this noble attempt by a computer is 12.1 trillion decimal places, held by Alexander Yee and Shigeru Kondo. It took them 94 days to make the calculation with a machine with 2 x Intel Xeon E5-2690 processor running 128GB of RAM and 96TB in total storage.

NASA’s Jet Propulsion lab only uses 15 digits to calculate interplanetary travel, while mathematician James Grime argues that just 39 digits of pi is enough to calculate the circumference of the known universe.

It’s hard to imagine Pi Day didn’t exist until 1988

The first party in honor of the amazing mathematical entity known as “pi” began in 1988 when Larry Shaw, a physicist at the Exploratorium, the San Francisco science museum, looked at the calendar and said, “March 14 — it’s the number pi. It’s Pi Day. Let’s celebrate!” Now Pi Day is marking its 30th anniversary. Today, Google marks the 30th anniversary of the math-inspired day with a special Doodle.

The Massachusetts Institute of Technology releases its undergraduate admissions decisions on Pi Day and starting in 2012, it began sending the verdicts at 6:28 pm, or “Tau time,” for the mathematical equation 2π.

In 2009, the U.S. House of Representatives passed a resolution in support of officially designating March 14 as Pi Day, so the holiday has some official backing in the U.S. but not yet enough to shut down post offices and schools.

Happy Pi Day! Enjoy and celebrate mathematics today.

Sadly, the world lost a great mathematician and physicist Stephen Hawking today on the Pi day and the birthday of another great mathematician and physicist Albert Einstein. Time and space are relative! May his noble soul rest in peace!