The diameter of a circle is equal to the diameter of a circle times pi. It is also equal to the radius of a circle times tau. Tau is twice pi, approximately 6.2831853071. Many people (myself included) feel that we should use tau instead of pi. It would make measuring angles in radians more intuitive.
Pi day is celebrated on March fourteenth, 3-14. Tau day is celebrated on June twenty-eighth, 6-28. Yesterday was Tau day.
A group of 8 of us went out for pizza for dinner last night for no reason other than I wanted to try this place. We ordered a couple of pizzas. My brother was wearing a math shirt, so a man from the next table came over to us, and we talked about math a bit.
A bit later he came over to us and commented "I see you're celebrating Tau Day with two pies."