Today is a very special Pi day since the “15” of 2015 carries the magical (technically irrational) number out to four digits (four digits to the right of the decimal point): 3.1415. And then there was a moment in the day–9:26 and 53 seconds–when the number was carried out to nine digits: 3.141592653!! Read more about Pi day (coincidentally Albert Einstein’s birthday) at this site here. How does this photo honor Pi day (no pies!?)? Because it features circles! Pi, in case anyone needs a refresher, expresses the constant ratio between a circle’s circumference and its diameter.