# What is Pi Day?

by kajohu

## Did you know that there's a day to celebrate the math constant "pi", 3.14....? (March 14) What will you do to celebrate pi?

No, I'm not forgetting an "e" at the end of "pi", but it would certainly be an appropriate and fun way to celebrate Pi Day with a circular fruit pie or pizza pie!

"Pi" or "π" is the math constant that is the ratio of a circle's circumference to its diameter, or approximately 3.14. Remember that the circumference of a circle is the measurement of the perimeter, or outside, of the circle, and it's diameter is the length across the widest part of the circle.

National Pi Day is thus celebrated on March (3rd month) 14. Will you be celebrating Pi Day this year?

 Circle

### First, What is Pi? (A Brief Refresher Course)

##### Pi = 3.14159....

Do you remember what the number pi is and what its significance is from your school math days?

If you're a mathematician or a scientist, of course you do -- you probably use it often.

Pi, represented by the Greek letter π is the math constant that is the ratio of a circumference of a circle to its diameter.

Circumference = the measurement around the circle, perimeter of the circle.

Diameter = the length of the line through the center of the circle.

The circumference, or perimeter, of a circle of any size is a little over 3 times the length of its diameter, or 3.14159 (etc.) times as long.

Pi is an irrational number, meaning that it can't be expressed exactly as a number or a fraction.   The first 50 digits of pi are 3.1415926535897932384626433832795028841971693993751.

And why was the Greek letter Pi or π chosen for this math constant?  Because Pi is the first letter of the Greek word for perimeter, or perímetros.

### March 14 is National Pi Day

March 14 is Pi Day, because March 14 can also be represented as 3.14, which is a good approximation of the math constant pi, or π.

Physicist Larry Shaw created Pi Day in 1988, where it was first celebrated at the San Francisco Exploratorium (museum for the ongoing exploration of science, art, and human perception).   To celebrate, museum staff and museum visitors marched around one of the circular spaces within the Exploratorium, and then ate pi(e)s!

In 2009, the U.S. House of Representatives passed a resolution that designates March 14 (3.14) as National Pi Day.

Schools around the country take advantage of this day to teach students in fun ways about the significance of this special number.

 Happy Pi Daykyz on Flickr.com, CC BY 2.0

### Pi Gifts for Pi Day

Here are a few fun gift ideas for Pi Day, or for any special occasion for your math and science family members and friends (my husband teaches high school physics, and my two sons are both in physics Ph.D. physics....these are the kinds of people these gifts are good for!).

This humorous button says "Come to the Nerd side!  We have pi!"

The t-shirt is representative of a number of cool pi shirts available on Zazzle.com.

On March 14, 2010, Google had this great pi doodle up on their page.  I'm hoping they have it up again this year.   This doodle shows different usages of pi, including for calculating the circumference of a circle, the area of a circle, the volume of a sphere, plus a couple other usages.

### Cool Pi Trivia

Cosine! Secant! Tangent! Sine! Three Point One Four One Five Nine!

Part of a college cheer

March 14 is also Einstein's birthday.  How fitting!   He was born in 1879.

Celebrate Pi Day to the Minute.
Celebrate pi on March 14 at 1:59 (π=3.14159)

Or even cooler, on  March 14, 2015, celebrate at 9:26 (π=3.1415926)

Pi Approximation Day is July 22, because in DD/MM format, this date is 22/7.
A good approximation of pi is the fraction 22/7 = 3.142857(with repeating 142857).

### Have a Pi Party

Eat a pizza pie, cut by this Pizza Pi Cutter.   Cutter is made of Pi plastic handle and two stainless steel blades.   (Hand wash only!)

Open a brew (or a soft drink) with the Pi Solid Steel Bottle Opener, and add pi shaped ice cubes to your drink!

 Pi Symbol Ice Cube TrayOnly \$9.99

### Kate Bush Sings Pi

So now you and your friends are settled in with your PIzza and PI-ice-cold beverage.   You may want to include a PIna colada, a pineapple, or some pine nuts to round out your PI Day meal!

Now it's time to sit back and relax to this beautiful song by Kate Bush, in which she sings a long version of PI!   I bet you've never heard a lovelier pi recitation!

Updated: on 05/25/2013, kajohu
5

### How Will You Celebrate Pi Day?

katiem2 on 03/13/2012

I'm so excited Pi day is almost here and I can't wait, did I ever mention pie is my favorite day so pi math is a good day for me as well.

katiem2 on 03/10/2012

I'm ready to go, I've ordered my pies from a very good local baker and will have a great day this Wednesday celebrating Pi Day, I;m having them include the Pi sign you added to your pie on this web page!!! Great Idea!

kajohu on 03/05/2012

It's so fun when kids get excited about something as unusual as Pi Day :-) I'm glad your kids like it, katiem2!

katiem2 on 03/05/2012

Oh yes thank you for the reminder, every year my kids get so excited about pi day, this year I won't forget to bake some pi to celebrate pi day. Last year my daughter wanted to take her math teacher a pie but she asked the night before and rather late, this year I will be on the ball. Thanks again :)

kajohu on 03/04/2012

Save a piece of chocolate pie for me :-)

ohcaroline on 03/04/2012

I think a nice piece of chocolate pie would be most appropriate. You've given me a reason to go for the pie on pi day. Thanks. :)

kajohu on 03/04/2012

Any reason to eat pie is a good day in my book :-) And might as well do it for pi day!