A little history, a little pie, and a few activities to get you in the mood!
Written by Adrienne M. Roehrich, Chemistry Editor
Pi Day, March 14, or 3.14 has been gaining popularity over the past few years. There’s a counter movement to promote Tau Day as well. I love that a geeky mathy thing that everyone learns in elementary school is so popular. It’s also a great excuse to eat some pie!
Pi or π is the ratio of a diameter of a circle to its circumference. It is a mathematical constant and sometimes called a constant of nature. It is commonly given as 3.14159 (and next year we get to celebrate Pi Day to the fourth decimal place!) but is an irrational and transcendental number, with no common fraction representation and the decimal form being neverending with no repeating pattern. Cool, right? (I love numbers!)
The history of π is also fascinating. Pi has been recognized for just about 4000 years and our earliest known determination of it was the Ancient Babylonians on a tablet, who recognized that the circumference of a circle was roughly 3 x the diameter, π = 3. Just about that same time, the Egyptians were also calculating pi, leaving behind the Rhind Papyrus as evidence.
In the early first millennium, both Archimedes of Syracuse, Greece and Zu Chongzhi of Baoding, Hebei, China, were using different methods to rigorously calculate pi. They represented pi in fractions, rather than decimals.
The Greek letter π was not actually used to represent this mathematical constant until the 1700s when it was introduced by William Jones and popularized by Leonhard Euler. Euler is well known for a number of theorems in mathematics and the angles used to specific the orientation of a rigid body called Euler’s angles.
Most recently, pi has been calculated to one trillion places beyond its decimal point. The accuracy of Pi Day varies, but many especially celebrate at 1:59 (am or pm). The most accurate celebration day in our lifetime will be 3/14/15 at 9:26:53.589, the likes of which hasn’t been seen since 1915 and won’t occur again until 2115.
Pi Day is often celebrated with pie! (What else?) So, the Venn Diagramm of Lovers of Pie and Lovers of Pi converge for the day. What kind of pie is appropriate for Pi Day? Any flavor will do, as long as it is round.
Besides eating pizza pie and following up with a dessert pie, what else can you do to celebrate Pi Day? There are tons of online Pi Day activity suggestions. Here are just a few resources:
 Visit the Pi Day website for nifty Pi Day Stuff
 Shirts, clocks, mugs, and more!
 WikiHow gives 8 tips (with lots of subtips) on Celebrating Pi Day
 Create pi ambience with wearing pi clothing
 Tell time in pi
 Have a pi recitation contest
 Run a pi (that’s 3.14 miles)
 TeachPi.org has over 50 activities related to pi
 Create a pi chain
 Dress as Albert Einstein (born on Pi Day)
 Compose poems, songs, and make pi art, then hold an exhibit
 Hold a Math workshop or symposium
 Edutopia refers to a number of other websites with pi activities
 Chiff has a few more local events highlighted
 Princeton’s entire Pi Weekend
 Education World has worksheets and party ideas for all grade levels
 Geometry, Trigonometry, Algebra II and more!
 National Council of Teachers of Mathematics bring on more ideas
 Play Monopily
You can also search for “Pi Day” and your city to see if there are local activities for you to participate in. In my locale of Seattle, for instance, The Seattle Children’s Museum has Pi Day activities starting at noon and the West Seattle Branch of the Seattle Public Library has activities starting at 3:14pm (of course!).
Should you want to make a pie on Pi Day, here is an Apple Pie Recipe.
Crust Ingredients:
 2 cups flour
 1/2 T. sugar
 3/4 tsp. salt
 3/4 cup lard
 1 small egg, beaten
 1/2 T. vinegar
 1/4 cup water
Crust Directions:

In a large bowl, sift together flour, sugar and salt. With a pastry blender or two knives, cut in lard until mixture resembles coarse crumbs. Mix together egg, vinegar and water, then add to flour mixture. Mix until dough is moist enough to form a ball.

Wrap in plastic and chill for 30 minutes.

Divide dough in half. On a floured surface, roll one half into a 12inch circle. Press dough into pie plate. Crimp to form decorative border, then prick bottom with fork.

Place in freezer while preparing pie filling. Makes one double crust pie.
Apple Pie Filling Ingredients:
 3 cups pared, cored and sliced apples (about 3 apples, really good with granny smiths)
 3 T. flour
 1 cup sugar
 1/2 tsp. cinnamon
 2 T. butter
 3 T. milk
Apple Pie Filling Directions:

Preheat oven to 375ºF.

Mix apples, flour, sugar and cinnamon. Stir gently. Pour into unbaked pie shell. Dab with butter and pour milk over filling.

Roll top crust same as bottom and lift onto filled pie or decorate with woven lattice top. Bake 4045 minutes. Filling for one pie.
Don’t feel bad if you miss celebrating Pi Day today. You can always celebrate Pi Day Approximation on July 22! What are your plans for Pi Day?
This post appears concurrently at the GeekGirlCon blog.
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