Dear All, I am delighted that so many readers explored the amusing problem of how long the sun can fall on a north-facing wall.
I liked the diagrams that Roger and Helmut prepared. The different approaches led to much the same answers, including Roger's once he had looked at the correct side of the wall! Willy says: You're right. Never and nowhere a vertical wall can receive sunlight over a longer period of time in a day. Helmut adds: Further on the pdf shows that the maximum of sun on a south wall is 12:00 hours but, at equinox not on summer solstice. This needs interpretation... For the maximum sun on a vertical *south* wall you have to place it on the ANTarctic circle where you get the same answer! Helmut is right that a south-facing wall gets 12 hours of sun at an equinox. This is true for any south-facing vertical wall in the northern hemisphere. You won't get 12 hours on the south side in the southern hemisphere! Alas, here it is raining so no sun at all, and in half an hour I am leading 20 visiting academics on a sundial walk walk:-( Enjoy the sun if you have it! Frank King Cambridge, U.K. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
