**Happy Pi Day**! Friday March 14 marks the celebration of “pi”, one of the tastiest confections, er, mathematical constants in the universe.

Exactly what is pi?

It all goes back to circles. The ancient Babylonians determined the area of a circle measuring the radius – a straight line from the center to the circle’s circumference – and multiplying the square of it by 3.125.

This number, further refined to 3.1415926 and now known to **10 trillion decimal places as of 2011**, was crowned ‘pi’ in 1706 after the Greek letter of the same name. Simply, pi’s the ratio of a circle’s circumference to its diameter. No matter the size of your circle, if you divide the length of its circumference by the diameter (= two times the radius), you’ll always get pi for an answer. That’s why it’s called a ‘constant’.

So who cares? People who like pizza for one. Which is the better deal – a medium, two smalls or a large pizza? Ask your server for the diameter of each, half it to find the radius, then apply the simple formula *pi times r squared* to determine the area.

Divide the area by the price and the one with the lowest price per area is the best deal. OK, that’s pretty nerdy.

Pi shows up in more places than your neighborhood pizza parlor. Anything involving circles, spheres and ellipses feature pi front and center which is why astronomy and architecture require healthy servings of pi for sustenance. Galileo, Copernicus and Kepler used pi in their calculations of the sizes, distances from Earth, and orbits of the planets. It pops up in statistics, mechanics, cosmology and even in Einstein’s Theory of Relativity equations.

One of my favorite pi debuts was in Carl Sagan’s book ** Contact**, which was later made into an excellent movie featuring Jodie Foster as the radio astronomer who first hears an intelligent signal from space. She describes the signal’s frequency as “pi times hydrogen”, referring to the radio signal emitted by hydrogen atoms in space (1.42 GHz), but multiplied by pi, a sure indicator of an intelligent origin.

Intelligence or not, pi’s an **irrational number** which means you can’t write it as a simple fraction. For instance it’s almost equal to 22/7 (22 divided by 7) but not quite. It’s closer yet to 245850922/78256799 but again, not quite. Pi’s digits never end when converted to a decimal. Nor does it contain repeating sequences of numbers of any length. Check it out yourself **HERE**.

Because we take anything that doesn’t yield to the human will as a personal challenge, people keep hitting up pi again and again, trying to unlock its secrets. Good luck. After 4.000 years it still has the upper hand, though we’ve partially tamed it for many practical purposes.

That’s why we celebrate not only its usefulness (and mathematics in general) but also pi’s tenacity every year on March 14. Why that date? Does 3.14 ring any bells? Now imagine the excitement next year March 14, 2015 at 9:26:53 a.m. Worth celebrating with an extra slice of pie, don’t you think?

I DO think so… and since it is my birthday too, I’ll beg an *extra* extra slice… if I may.

Just curious: what other numbers are there that are constants like Pi? There’s the speed of light. I sometimes hear about something called a cosmological constant, but I have no idea what that number is or why it is important. Are there others?

As always, I enjoy reading your posts, Bob! Thanks so much!

Happy Birthday Bob! May the force of pi be with you. Yes, there are other constants such as G, the gravitational constant (= 6.67384 × 10-11 m3 kg-1 s-2) and the fine structure constant a (= 7.29735257×10−3) that characterizes electromagnetic interactions and many more. If you’ll ever in need, you’ll never run out here: http://www.ebyte.it/library/educards/constants/MathConstants.html

Carl Sagan’s “hydrogen frequency times Pi” actually means the aliens where sending the message only for us. It means that they knew us very well: only in a decimal numeral system does Pi equal 3,1415etc. But ore important, the Herz is based on our very earthly SI international system of units. Carl Sagan would have though of that, or am I missing something?

Sebastien,

No, I think you’re absolutely right. And indeed, in the movie, they were intending it only for us.

Come on Bob! Everybody knows pi r NOT squared! pi r round! CAKE r squared. : ) Keep smiling, even math CAN be fun.

Gordy,

Good one Tastier too.

Bob, I like your favorite pie chart.

Just guesstimating, but it looks like you’ve eaten about one pie radian.

Richard,

And I feel positively radiant for doing so.

I still regret the day when I had to utter the unthinkable in order to get the attention of a restless group of scientists:

http://youtu.be/V98soOyQWKY