Hi Jeffery you are actually calculating the horizontal angle indicated as 'angolo' on the diagram below ie. deviation of the Sun from the wall under consideration. Hope this helps, Alexei
[image: image.png] On Mon, 26 Jun 2023 at 16:37, Jeffery Brewer <jeffery.bre...@gmail.com> wrote: > I'm attempting to measure the declination of a wall using a method > described on this web page of The Sundial Primer > https://www.mysundial.ca/tsp/wall_declination.html (also described in > "Sundials: Their Theory and Construction" by Albert E Waugh Chapter 10). > > Referring to Figure 1 of The Sundial Primer reference, "The direction of > the sun relative to the wall, θ, can be determined as follows: θ = arctan( > AB / Nail Length)°" If I label the ends of the nail with points C and D > (see figure below) then the formula can be understood as θ = arctan( AB / > CD )° > > [image: Figure1Modified.jpg] > > With my very rudimentary understanding of basic trigonometry, I understand > how the formula would work for a simple right triangle existing in a single > plane, but not how it works here. It seems to me that AB lies in an XY > plane parallel to the wall, but CD lies along the Z axis, perpendicular to > the XY plane. The shape described by ABCD is a sort of twisted rectangle > and I don't understand how the formula applies. > > I'm almost certainly thinking about this wrong (it feels like an optical > illusion where I can only see the vase and not the faces). > > [image: image.png] > > If anyone can help me "see the light" I would appreciate it. > > Jeff Brewer > > > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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