Every day I would come home from school and my sister would ask me, "what did you learn today?" Sometimes I'd stammer and tell her I hadn't learned anything useful, while other days I'd happily tell her I read Phaedo or learned what an isotope is. In the 'Does your interest in learning cease at a certain age?' thread jimmysynder reminded me of this old tradition we had. So today, tomorrow, and any day you get the chance, post something you learned. Anything from a new physics equation to a new word - whatever it is regardless of how technical or simple. I'll start. Today I learned how to measure how big the Earth is using only the sunset when I'm laying down and when I'm standing.