How to determine the formula to calculate this position of reflected Sun? I created a geometrical simulation of how the Sun is reflected on a wall along the day and along the year, using Geogebra:

https://www.geogebra.org/classic/dckhbc8h
Playing with parameters, I found an oddity: in some specific cases, changing the &quot;season angle&quot;, i.e. inclination of su circle w.r.t. horizon, I can see the &quot;sun reflection line&quot; always passing in same point on the wall along whole year:



Overlapped:

Is this a real behaviour or just an error in my simulation?
Does it happens always at same time of the ay? My simulation currently does not show the times along the &quot;sunLine&quot; segment.
How could I build a Geogebra formula to directly draw the &quot;convergence point&quot; of all the sunLine lines along the year?
When the &quot;sun angle&quot; is zero, the position of the &quot;sun&quot; doesn't depend on the season angle, so the lines will cross at the point that is the image of the sun at &quot;sun-angle 0&quot;
One important aspect in your model is that the season doens't change the &quot;angle&quot; but the position of the sun.  In summer, the sun rises and sets in the north East and north west and describes a small cirle around the north celestial pole. In winter it rises and sets in the southeast/west. And only at the equinox does it describe a great circle.