Dear Dan, The approach that you describe does indeed show you how long the sun can theoretically shine on a vertical wall, for a given solar declination, provided (as you say) that you know the times the sun rises and sets.
Now a simple exercise... What is the maximum amount of time the sun can shine on a vertical wall? You can choose the latitude and you can choose the orientation of the wall and you can choose the solar declination. Frank King Cambridge, U.K. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
