Dear Gianni, Mea culpa! You are of course right. The summer solstice arc indeed curves upwards on a cylindrical surface.
I was assuming that the surface was made of flat segments (as in the external photograph) but this is not so. > - The higher line (at ¾ of the height of the > doors) (aluminium) is the 70° almucantarat > (constant-altitude curve) I hadn't noticed this but, again, you are right. Yes, I agree with that. > - The compass rose is of 24 points because from > each of them comes out one of the vertical azimuth > lines True, but azimuth lines are usually separated by 22.5 degrees or 11.25 degrees. > I don't understand why the planners have used a > program that solves Kepler's Laws... I agree. Kepler's laws are fine for an ideal case but the Earth's orbit is much more complicated than pure Kepler. A good exercise is to implement the Meeus algorithms. This takes a long time but when you have finished you understand how messy the Earth's orbit really is! Best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
