On Sat, 7 Jun 2003, [ISO-8859-1] Anselmo P?rez Serrada wrote: > I think I can help you on this. They use a very elegant method to draw a > sundial based on geometrical > affinity that traces back to our High School days: > > 1. Draw two concentrical circles : one of radius r and the other one of > radius r*sin(Lat) > 2. Now draw a sheaf of 24 equispaced lines from its center as if it > were an equatorial dial. > 3. These lines intersect the circles at points I' and I'', II' and > II'', and so on up to XXIV' and XXIV''. > 4. Now trace horizontal lines from the inner points and vertical lines > from the outer points. Let's call > I the point where the lines from I' and I'' intersect, II the point for > II' and II'', and so on. > 5. If we connect these points we just have the analemmatic ellipse, > right? Well, but if we trace lines > from the center to these points we get a horizontal dial for that > latitude. Isn't that nice?
Very well described, Anselmo! Everything agrees perfectly with the original article, except you have one circle of radius 1 and the other of 1*sin(lat). Now, if I am looking at this correctly, that would make the second circle smaller than the first (and also avoid the singularityat 0 degrees!) However, is the ratio of the two circles' size the same in both constructions? I'll have to draw them up, and scale one to match the other... Dave 37.28N 121.97W -
