*Researched and written by Elizabeth O’Dea, (Indus Space Staff, Math major).*

Happy Pi Day!! Did you know March 14th is annually celebrated as Pi (Π) day?

What is π? It is a mathematical constant, calculated as a ratio.

π = circumference of circle/ diameter of circle. Pi is used in the calculation of circumference, area, and volume in all circular or spherical shapes.

To many people, π is only thought of in the basic math context, and they don’t see the utility of it in everyday life. But engineers and construction workers, for example, need π to be able to calculate things in order for them to work properly and fit in their desired places.

We’re here to tell you that π is used for so many wonderful things, including clocks, sports, navigation, and certainly in space exploration. Read all the way through, there’s a fun activity at the very end!

## What's in a number?

π has an infinite number of digits and millions of them are known to us, but for the most part we use a maximum of a dozen digits. In general, 3 digits of π is the most common approximation used, but for more precise calculations we typically only use about 12 digits of π.

## History of Pi

Pi has been around for approximately 4000 years. It all started with the ancient Babylonians who approximated π to be 3 and ever since many people have been studying and analyzing π.

After the Babylonians, the Egyptians found an even closer approximation of π that was still not quite right. Eventually, Archimedes of Syracuse became the very first mathematician to use an approximation of pi for calculations. He was able to estimate the range in which π was found and used that to calculate the circumference of circles.

Shortly after, the Chinese mathematician Zu Chongzhi found his own approximation of π simply by performing thousands of calculations and square roots of a shape resembling a circle.

π has been around for thousands of years, explaining the utility and importance of this number. However, π has been around for so long, but the symbol, **π** , which is taken from greek letters, has only been around since the 1700s. In 1706, William Jones decided the symbol for π and ever since it has been used across the world.

## Why Celebrate Pi Day?

π Day is on March 14 every year due to the significance of the date. 03/14 represents the first three digits of π and hence every year π day falls in March.

π Day is also the birthday of many important people linked to space exploration. Did you know: March 14 is **Albert Einstein**’s birthday? If you don’t already know who that is, he is a famous theoretical physicist who developed the theory of relativity. His research contributions has allowed us to further understand space, gravity, and the universe in many important ways.

Additionally, Italian astronomer Giovanni Schiaparelli (discovered canals on Mars), Pedro Duque (first Spaniard in space), American astronauts Frank Borman (Gemini 7/Apollo 8 missions) and Gene Cernan (last man on the Moon) all share the same birthday on π day.

These people all have an important role in the discovery and study of space and have all had to use π in their studies.

## Common Items That Rely on Pi

### π in sports!

Anything in this world in the shape of a sphere or circle that is man made, π was most likely used in it’s creation process. Things like basketballs, baseballs or tires all need π to determine their shape and size. Without π, every basketball would be shaped differently and would never bounce properly making the sport very difficult. .

### π at home!

In addition, your house or apartment would never be able to function. If π never existed your pipes wouldn’t be able to flow properly and many things you don’t even realize would cease to exist. Washing machines, photocopiers, blenders, and fans all use ball bearings, which are in the shape of a sphere and require π to be created. .

## Pi in Space: What's the deal?

#### π plays a huge role in many aspects of space exploration. We’ve picked the top 10 instances π has been directly used in mission planning and calculations.

### Parachute Design

Engineers use π to calculate the size of parachute to create drag and slow any spacecraft as it lands safely on Mars!

### Safely land onto Mars

π is also used to determine the uncertainty for where a lander or rover may land on Mars. While all efforts are made to select a target landing site that meets all scientific and engineering goals, uncertainties need to be factored in. Uncertainties include effects from wind, air density, speed and position of the spacecraft.

### Study quakes and tremors

Still staying on Mars, π is being used in calculations to study quakes and tremors, aka marsquakes! Scientists use signals captured by the InSight lander to determine when quakes occur and where!

### Eyes on Saturn

Mission engineers used a π-transfer method twice during the Cassini mission around Saturn to gain new perspectives of both Saturn and its moon Titan!

### Capturing pictures of other surfaces

Scientists use π when calculating the total surface area and use it to determine how many images need to be taken in order to map a full planet or body!

### Searching for exoplanets

Scientists use π in calculations when searching for extra solar planets (aka exoplanets). Ground and space-based telescopes observe the brightness around other stars, the dip in brightness from the star can help determine the size of any orbiting exoplanet!

### Is that you Goldilocks?

Scientists also use π to calculate the extent of the habitable zone around stars. A zone is considered habitable where water is present in liquid form instead of gas (close to a star) or ice (too far from a star).

### Calculate the orbital period

Scientists use π + Kepler's 3rd law to calculate orbital period of an exoplanet around its parent star. This helps determine if a planet is within the habitable zone or not.

### Communicating with Earth

π is used often in math equations to send signals to and from spacecrafts and antennas on Earth! Such as the Deep Space Network.

### Uncovering the heart of Pluto!

π was used to determine the size of Sputnik Planitia(heart feature) on Pluto!

**There are so many other ways **π** is used in space exploration.**

**Now you can always look back at **π** as an amazing and interesting topic when thinking about the space exploration. **

# Complete These Challenges!

Test your π knowledge by completing this self paced Kahoot quiz!

Check out NASA's annual π

challenge and look for solutions to be revealed soon.

Image Credits: NASA/ESA

Research Source: NASA