## It may be irrational but pi plays an important role in the everyday work of scientists at NASA.

## What Is Pi ?

Pi is the ratio of a circle’s circumference to its diameter. It is also an irrational number, meaning its decimal representation never ends and it never repeats. Pi has been calculated to more than one trillion digits,

## Why March 14?

March 14 marks the yearly celebration of the mathematical constant pi.

More than just a number for mathematicians, pi has all sorts of

applications in the real world, including on our missions. And as a holiday that encourages more

than a little creativity – whether it’s making pi-themed pies or

reciting from memory as many of the never-ending decimals of pi as

possible (the record is 70,030 digits).

While 3.14 is often a precise enough approximation,

hence the celebration occurring on March 14, or 3/14 (when written in standard U.S. month/day format), the first known celebration occurred in 1988, and in

2009, the U.S. House of Representatives passed a resolution designating

March 14 as Pi Day and encouraging teachers and students to celebrate

the day with activities that teach students about pi.

## 5 Ways We Use Pi at NASA

Below are some ways scientists and engineers used pi.

## Keeping Spacecraft Chugging Along

Propulsion engineers use pi to determine the volume and surface area of propellant tanks. It’s how they size tanks and determine liquid propellant volume to keep spacecraft going and making new discoveries.

## Getting New Perspectives on Saturn

A technique called pi transfer uses the gravity of Titan’s moon, Titan, to alter the orbit of the Cassini spacecraft so it can obtain different perspectives of the ringed planet.

## Learning the Composition of Asteroids

Using pi and the asteroid’s mass, scientists can calculate the density of an asteroid and learn what it’s made of–ice, iron, rock, etc.

## Measuring Craters

knowing the circumference, diameter and surface area of a crater can tell scientists a lot about the asteroid or meteor that may have carved it out.

## Determining the Size of Exoplanets

Exoplanets are planets that orbit suns other than our own and scientists use pi to search for them. The first step is determining how much the light curve of a planet’s sun dims when a suspected planets passes in front of it.

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