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Happy Pi Day!

As March 14th, "Pi Day" approaches, a look at how NASA uses this number to explore space.

Posted 2021-03-06T20:58:16+00:00 - Updated 2021-03-06T21:05:08+00:00

Tony Rice

, NASA

Sunday, March 14 is "Pi Day", a celebration of the approximate ratio of the circumference of a circle to its diameter, Pi Day was recognized by Congress in 2009 as well as the United Nations.

Locally Pi Day celebrations include a Pi Day Scavenger Hunt at Pullen Park in Raleigh and Virtual Pi day at Kidzu children's museum in Chapel Hill.

Pullen Park lines up Pi Day, St. Patrick's Day activities for families

Bull City Burger and Brewery in Durham, Blaze pizza locations, and Bond Brothers in Cary along with Slice Pie Company are offering Pi Day specials. Be on the look out for other discounts at pizza and other restaurants this week.

We couldn't explore space without pi

NASA calls pi the "Swiss Army knife of numbers". From measuring the size of a single atom to the size of our universe, the ratio of the distance around it (circumference) to the distance across (diameter) is always equal to pi.

While the fuel tank in your car is more-or-less like a box, NASA's fuel tanks on the ground and in space are more spherical to accommodate fuels stored at high pressures. Propulsion engineers use pi in calculating the size and weight of those tanks as well as how much fuel they can squeeze in there.

The launch pad facilities focus on the space shuttle. The white sphere stores liquid hydrogen fuel that will power the shuttle's three main engines. On the other side of the complex, an identical storage tank holds liquid oxygen, also for the main engines. Photo credit: NASA

Engineers used pi extensively in designing the parachute with slowed the Perseverance rover, and previous missions as they landed on Mars. It also helped the, encode a message for fans to decode.

From colors to Morse code, secret messages appear as Mars rover gets to work

Scientists use pi to find planets outside our solar system. By combining information about light coming from distant stars changes as an orbiting planet passes in front, with the formula for the area of a circle, we can come up with a pretty good estimation of the planet's size.

Just knowing the circumference, diameter and surface area of a crater can tell scientists a lot about the asteroid or meteor that created it.

How much pi is enough?

In 2019, Google developer advocate Emma Haruka Iwao used the company's cloud infrastructure to calculate pi to 31.4 trillion decimal places, beating the previous record by more then 8 trillion. This took 25 virtual machines nearly four months and required 170 terabytes of memory, roughly equivalent the printed books in the Library of Congress.

NASA's Jet Propulsion Laboratory (JPL) uses 15 decimal places (3.141592653589793) for interplanetary navigation. Why not more?

15 digits are plenty to calculate the circumference of the Earth to accuracy within the size of a molecule according to Marc Rayman, JPL's Chief Engineer for Mission Operations and Science.

Consider Voyager 1, the furthest human-made object from Earth, currently 14.1 billion miles away. If used that 15th decimal place approximation of Pi to calculate size of the circle Voyager is within approximate of Pi, the result would be off by less than 2 inches.