Here’s 255,032,236 Square Kilometers of Pi Day. More or Less.

Bad Astronomy
The entire universe in blog form
March 14 2013 1:33 PM

Happy Pi Day!

In the United States, today is the nerdiest of unofficial holidays: Pi Day (or really, π Day), because as we write dates here, today is 3/14, the first three digits of the eponymous number.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Pi is one of the most important of mathematical numbers, popping up everywhere in physics. Most people know it because it’s how you get the circumference of a circle:π x the diameter (or 2 x π x the radius).


It’s also how you get the surface area of a sphere: 4 x π x radius2. In honor of that, NASA released a photo showing half the surface area of our planet today, about 255,032,236 square kilometers (98,034,392 square miles) worth of it:

Earth from space
Happy Pi Day, from the GOES 13 weather satellite.

Image credit: NOAA/NASA/GOES Project

Pretty, isn’t it? To be fair, this is slightly less than half the Earth, since the satellite is about 36,000 kilometers (22,000 miles) above the Earth, and you'd need to be infinitely far away to see exactly half (due to the horizon problem). Still, close enough.

I like how they chose an image taken today by GOES 13, an Earth-observing weather satellite, which looks down upon the western hemisphere, including the U.S. In other parts of the world, dates are written in the form DAY-MONTH-YEAR, so to them today is (ignoring the year) 14-3, which doesn’t help. I guess for everyone else, π Day would be on the 31st of April.


π really is amazing. It's irrational, which means it cannot be exactly represented as the ratio of two other numbers. It goes on forever after the decimal point, never ending and never repeating (some numbers, like 1/9, are just repeating numerals when expressed as a decimal). That seems so counterintuitive, but it’s just the way numbers are. The Universe is under no obligation to conform to our common sense. More likely, our brains didn’t evolve to grasp such things easily. Good thing we invented math to figure this stuff out!

Otherwise, we might never have discovered the elegance that is the greatest equation of all time:

eiπ + 1 = 0

where e is the base of the natural logarithm, and i is the square root of -1. This is called the Euler Identity, and the more you think about it the more your brain will twist into a Möbius strip.

Anyway, π really is amazing. Did you know it pops up in an equation that describes how the Universe itself behaves as it expands? It’s related to prime numbers. It appears in so many integrals it would be impossible to list them all (here are a few). You can add up an infinite series of numbers to get π.

It’s so important that Carl Sagan wove it into the very fabric of his fantastic book Contact (the movie was based on it, and while very good, the book’s even better). I won’t spoil how, but you have to read to the very last page.

So π may be the most important single number in the entire cosmos. Take a moment today to contemplate any or all of this information; you’ll be the better for it. Pondering such things expands the brain, renews our sense of wonder, and adds to the joy of life.

C’mon! Who doesn’t want a slice of π?

Pi pie!
Pi are round.

Image credit: Medea_material on Flickr, used under the Creative Commons license.



Smash and Grab

Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?

Stop Panicking. America Is Now in Very Good Shape to Respond to the Ebola Crisis.

The 2014 Kansas City Royals Show the Value of Building a Mediocre Baseball Team

The GOP Won’t Win Any Black Votes With Its New “Willie Horton” Ad

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?


Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

One of Putin’s Favorite Oligarchs Wants to Start an Orthodox Christian Fox News

These Companies in Japan Are More Than 1,000 Years Old

Trending News Channel
Oct. 20 2014 6:17 PM Watch Flashes of Lightning Created in a Lab  
  News & Politics
Oct. 20 2014 8:14 PM You Should Be Optimistic About Ebola Don’t panic. Here are all the signs that the U.S. is containing the disease.
Oct. 20 2014 7:23 PM Chipotle’s Magical Burrito Empire Keeps Growing, Might Be Slowing
Oct. 20 2014 3:16 PM The Catholic Church Is Changing, and Celibate Gays Are Leading the Way
  Double X
The XX Factor
Oct. 20 2014 6:17 PM I Am 25. I Don't Work at Facebook. My Doctors Want Me to Freeze My Eggs.
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
Brow Beat
Oct. 20 2014 9:13 PM The Smart, Talented, and Utterly Hilarious Leslie Jones Is SNL’s Newest Cast Member
Oct. 20 2014 11:36 PM Forget Oculus Rift This $25 cardboard box turns your phone into an incredibly fun virtual-reality experience.
  Health & Science
Medical Examiner
Oct. 20 2014 11:46 AM Is Anybody Watching My Do-Gooding? The difference between being a hero and being an altruist.
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.