Circle the date! It's Pi Day today!
Meteorologist/Science Writer
Tuesday, March 14, 2017, 9:01 AM  Happy Pi Day, the annual celebration of the incredible, mysterious and irrational mathematical constant known as .
First of all, what is ?
Sure, it's a math constant. It's equal to 3.14, or 3.1415926 or 3.1415926535897932384626433832795  depending on what kind of calculator you use, although it goes on for much longer (see below). We use it in calculations in geometry and trigonometry, mainly having to do with circles and ellipses and so forth, and by extension, it shows up in the sciences  like physics, astronomy and meteorology, just to name a few examples.
But what is , really?
Simply enough, is the ratio of a circle's circumference to its diameter. Draw a circle 1 metre across and its circumference will be metres. A circle 1 centimetre across will be centimetre around.
The circumference of a circle being traced out in units of its diameter. Credit: Wikimedia Commons
OK, but what makes so special?
is an irrational number  one that never repeats and never ends. As such, to the best of our considerable knowledge of mathematics and the universe, we'll probably never know its exact value.
As the above circle unrolls, and it's compared to a ruler laid on the ground, the end of the circle will not fall exactly on one of the marks on the ruler. In fact, no matter how close together those marks are, and how small of a space they measure, the end of the circle will never fall exactly on the lines, ever.
As of October 2014, has been calculated to 13.3 trillion decimal places, which took a computer 208 days to complete!
Even with that incredible feat of computation, we still haven't found the end of it, or found any repeating pattern in the numbers, and it's very likely that we never will, no matter how much knowledge we accumulate or how powerful our computers become. That's why asking a computer or robot to compute the last digit of was such a good trick to use in science fiction stories. If the computer or robot didn't overload in the process, it at least bought you some time to escape.
Perhaps if we were able to look at our universe from the outside, we'd be able to see resolve down to a simple, rational number. From here, inside the universe, this mathematical constant holds as an enigma of the cosmos.
Fortunately, the cosmos is forgiving enough that we don't need to know to the last digit in order to produce useful results.
CLICK BELOW TO WATCH: The fine people at YouTube's Numberphile (who appropriately use as their user icon) show how to calculate , using pies.
Is there anything special about this particular Pi Day?
March 14 was chosen specifically because it comes out as 3/14 when we write the date out using only numbers. Usually, we extend that into the hours, minutes and seconds to produce more digits, so that in any year, on March 14, at 1:59:26 (am or pm) we can get the first 8 digits of .
In 2015, for the only time in the past century and the only time for the next century as well, we got even further, since the year was added to get 3/14/15 9:26:53  the first 10 digits of .
In 2016, we couldn't accomplish anything quite like that, but by calling it "rounded pi day"  as rounding off to four decimal places gives us 3.1416, or 3/14/16 on the calendar  we were able to celebrate all day long!
Now, in 2017, we're not getting anything special out of 3/14/17, but that's no reason not to celebrate!
So, how does one celebrate a mathematical constant?

Conveniently, the name of this particular constant happens to be a homonym for a very tasty dessert treat  pie!
Apple pie, cherry pie, blueberry pie, strawberryrhubarb pie ... even pizza pie.
As long as it's round, it will do just fine.
Do we celebrate any other scientific or mathematical constants?
Indeed, we do!
There's Pi Approximation day, on July 22, since 22/7 is a fraction used to approximate (it comes out as 3.14285714...)
Eday, either on January 27 or February 7  depending on whether you write your dates day first or month first  celebrates Euler's Constant, 2.7182818 (remember your 'natural logarithm', ln?).
For the chemists, there's Mole day, on October 23 (specifically between 6:02 am and 6:02 pm), since one Mole of a substance contains 6.02x10^{23} atoms or molecules of that substance.
Then there's Tau Day, on June 28, which celebrates , a constant that is equal to 2. Or, is 1/2, depending on which side of the rivalry you're on ... and yes there's a rivalry there.
Why? Because a circle is defined as "the set of all points in a plane that are at a given distance from a given point", or in other words, a circle is by its radius, not its diameter. So, the equation for circumference is really C = 2r = r. So, if you want to make the argument, technically makes a better mathematical constant. Unfortunately, while may be better mathematically, it does not have a tasty food associated with it.
For more on and Pi Day, go to piday.org, and if you'd like to try out some cool uses of , check out NASA's Jet Propulsion Laboratory Pi Day 2017 page!