Happy Pi Day! Honoring the big number that begins with 3

Pi Pie, created at Delft University of Technology, applied physics, seismics and acoustics.

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’.

The parts of a circle – the encompassing circumference, the radius and diameter, equal to 2x the radius. Pi is the ratio between the circumference and diameter of a circle.

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.

Jodie Foster as radio astronomer Dr. Ellie Arroway in ‘Contact’. Credit: Robert Zemeckis

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.

My favorite pie chart.

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?

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

9 thoughts on “Happy Pi Day! Honoring the big number that begins with 3

  1. 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!

  2. 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?

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