Ah, but the problem specifies "flat" surface. I took this to rule out convex-polygonal or elliptical/circular. I believe that every truly flat surface with no other obstructions in the way would get some glimmer of sunlight. If the surface is facing north and is predominantly in the shade, it will still be illuminated during morning and evening hours of the summer when the sun rises in the northeast and sets in the northwest. Even if the surface is facing down (!) it will catch rays at sunrise and sunset, assuming that it is high enough to clear any surrounding obstructions including mountains, foliage, etc.
At 09:39 AM 7/19/99 -0500, William P Thayer wrote: >Big enough of course to fit every dialist that deserved it; but what I mean >is this: > >>1. Is there any flat surface anywhere that never gets sunshine at some >>moment during the year? > >If you mean direct sunlight, yes, lots of them. Trivially, any point >adjacent to, and away from the equator from, a vertical wall, >convex-polygonal or elliptical/circular in plan, the ends of which cast >shadows on it even at summer sunrise and sunset. Tof produce a minimum >single point, the arc traced by such a wall would not have to be great, >although it increases with latitude. > Extending that, there must be a zone of perennial shade -- you guys with >computers can calculate the general formula for its shape and extent based >on the latitude and the height of the wall -- including points not >immediately adjacent to the wall. > >Practically speaking, this is the principle behind the urban layout of many >old Mediterranean towns: narrow streets make for constant shade in the >summer; if in addition they are not straight, they also temper winter >conditions. I noticed this in several towns of central Italy; one of which >-- Pitigliano, in Tuscany -- has a sundial in about the only place it can >have one near ground level: in a piazza where the streets widen out. > >Geographically, there must be plenty of deep non-N-S valleys, and surely >steep enough mountains act as my walls, above, for places on their >"leeward" side so to speak. > >The question then becomes: "Where is the *largest* such surface on Earth? >(Now there's a project...!) A similar question would be "Where is the >largest *volume* of air on Earth never to see direct sunlight?" > >*** >BTW, did anyone see the special on Noah's Ark last night? in which God's >rainbow was shown with the colors backward... A miracle indeed! > > >Bill Thayer > LacusCurtius >http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman > >
