Many around the world spent today celebrating the widest known mathematical constant, that share’s it’s name with a tasty treat:

π

The celebrate today because as March 14, or 3.14, it is a representation of π.

However this is wrong.

π in decimal (base-10) is 3.14159…, however, the calendar is not based on a base-10 system. So when is the real “pi day?”

We could consider a year to be like a circle, in that at the end (December) it connects right back to the start (January). In this representation we could represent the total number of days in a year (365.25) equal to the total angle of a circle (360 degrees, or 2π radians). This system would make “pi-day” to be approximately July 1st (or 2nd on a leap year, which also helps deal with rounding errors). This would also give us a 2π day on New Year’s Eve.

Or perhaps we should use the year’s total number of days as a base of counting, in which case π would have to be converted to that base and that would be the date. (Check my math perhaps) I think this date works out to April 24th or 25th (depending on leap years again).

However, explaining to people why you’re calling April 25th, or June 1st pi day and eating pie (which I did indulge in today), might take longer than the brief amusement provided by the idea.

I didn’t celebrate pi day, even though when asked I always say pi is my favorite number. It just sounds better than picking out any old number! 🙂

I’m not entirely sure what you mean by “use the year’s total number of days as a base of counting”, but it looks to me like you’re trying to find the day N such that 365/n≈π, in which case N would be the 116th day of the year, which would be April 26. Since 366/π=116.5015…, this would round up to 117, which gives us April 26 in a leap year, as well.

If we use Earth’s orbit and radians, 2π and 0 would occur on the same day. My preference would be to use perihelion for the zero point, which would mean Pi Day would coincide with aphelion. Perihelion was on January 4th this year, and will be on January 3 next year, while aphelion will be on July 4 this year and July 6 next year.