Pi Day, the informal holiday beloved by math enthusiasts — and even by the math averse — is here! March 14 marks the yearly celebration of the mathematical constant π (pi).

**What is Pi?**

Pi (3.1415….) is the ratio of circumference to diameter in a circle. Any time you want to find out the distance around a circle when you have the distance across it, you will need this formula.

Despite its frequent appearance in math and science, you can’t write pi as a simple fraction or calculate it by dividing two integers. For this reason, pi is said to be “irrational.” Pi’s digits extend infinitely and without any pattern, adding to its intrigue and mystery.

**How Do We Use Pi at NASA?**

**Measurements: **Pi can be used to make measurements – like perimeter, area and volume.

For example, sometimes we use lasers to explode ice samples and study their composition. In this scenario, we can uses pi to calculate the width of the laser beam, which in turn can be used to calculate the amount of energy, or fluence, that hits the ice sample. A larger fluence equals a bigger explosion in the ice.

**Commanding Rovers:** Pi is also used every day commanding rovers on the Red Planet. Everything from taking images, turning the wheels, driving around, operating the robotic arm and even talking to Earth!

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