fine structure day Share definition Flag Like Pi day, but using the fine structure constant 1/137 = 0.00729. So, the day is July 29th. You: "Happy fine structure day" Random Guy: "What the hell is that?!" fine structure day by physics nerd March 15, 2013 0 0 Get merch Get the fine structure day mug. Buy Now — $32.95 See more merch