Sometimes I’m slow on the uptake. On Saturday, when June and I were treating our oldest son, Mark, to lunch on his birthday, Mark said, “Do you want to join me for lunch at the Pi Bar Tuesday?” It’s a restaurant I’d heard of but never been to. We agreed on a time, and it just occurred to me this morning that we’re going to lunch in honor of Pi Day, today, 3.14 (March 14).

March 14, written 3.14, captures the first two decimal digits of pi. Some people pause for a moment of silence at 1:59 pm in honor of the next three digits. Pi’s digits go on infinitely and I think the record for memorized pi digits is 70,000. That’s a lot of digits and completely unnecessary. Someone asked a rocket scientist at the Jet Propulsion Laboratory (JPL) how many digits they use in their calculations:

To start, let me answer your question directly. For JPL’s highest accuracy calculations, which are for interplanetary navigation, we use 3.141592653589793. – Marc Rayman, who first asked the question as a 6th grader!

He went on to explain that using an approximation to pi out to 15 decimal places means that if you wanted to calculate the circumference of the earth given its diameter of just over 7900 miles, your answer would be off by about the size of a molecule.

Do you not know? Do you not hear? Has it not been told you from the beginning? Have you not understood from the foundations of the earth? It is he who sits above the circle of the earth, and its inhabitants are like grasshoppers; who stretches out the heavens like a curtain, and spreads them like a tent to dwell in; who brings princes to nothing, and makes the rulers of the earth as emptiness. (Isaiah 40.21 – 23, ESV, emphasis mine)