# Pi Day celebrates 3.14159… ## Happy 3.14159… Day!

When we measure the distance around a circle (starting and stopping at the same point) compared to the distance measured across the circle’s center, we are computing a ratio (and calculating a number). As intuitive and curious as this ratio seems — a simple measurement of girth versus breadth — the resulting number is a mathematical constant known as pi, which we notate by the Greek letter, π, and define as π = C/d. Here C is the circumference of the circle, and d is the diameter of the circle. We learn that the distance around any given circle is a little more than three times the distance across it.

Pi itself is an irrational number. Irrational numbers are numbers that have no terminating digit after its decimal point, including no terminal repeating digits or terminal sequence of digits. With these concepts in mind, we invite you to view the first million digits of pi at the following link: One Million Digits of Pi. Interestingly, only pi’s first 39 digits are needed to calculate the spherical volume of our entire universe (Pi Day Website).

Yet, even though pi cannot be expressed as a rational number (and for that matter a common fraction), it is approximated by the fraction 22/7. Most people, however, choose to simply memorize a certain string of digits from pi, such as π = 3.14159.

Pi is used in the following non-exhaustive list of formulas:

• Circumference, C, of a circle: C = 2πr
• Area, A, of a circle: A = πr2
• Volume, V, of a cylinder: V = πr2h
• Volume, V, of a sphere: V = (4/3)πr3

For each of the aforementioned equations r is radius, and pertaining specifically to the volume of a cylinder, h is height.

#### Today is the 30th anniversary of Pi Day!

##### — Pi Day Contest (sponsored by Ashland Creation Colloquium) —

Celebrate Pi Day by taking NASA’s out-of-this-world mathematical challenge (click this internal link to download the novelty poster for the Planet Pi challenge).