All of these ideas using lasers, auxiliary sundials and transparencies all sound like they would help in drawing the sundial face, but I don't think they will precisely place the dial drawing on the ceiling or help to correctly align a declining or inclining mirror.
I think you all are minimizing the importance of the "optical lever" effect. Very slight errors in placing the transparencies, lasers and auxillarily sundials can cause the sunspot on the ceiling to be way off. For example, let's consider a large room with a maximum sunspot projection distance from mirror to ceiling of say 25 feet (8 meters). Let's see how far off the sunspot will be if the mirror is tilted just 1 degree from where the design specs say it should be. (To make the math easier, imagine that the mirror is in the center of a sphere projecting a sunspot onto the interior wall of the sphere). A circle of a 25 ft. radius has a circumference of 157ft.or 1884 inches (4800 cm). So, 1 degree = 1884/360=5 in. (13 cm.) This shows that just a 1 degree error in mirror alignment causes an unacceptable 5 inch error in sunspot location. Misalignments of the laser, transparency or an auxiliary sundial would cause similar errors. (There might also be an additional error caused be the sunspot being refracted from passing through the glass window or from uneven surfaces or tilts in the ceiling) In my opinion, these layout and construction methods might help as as guide to roughly get an idea for the final look of the dial or as a check, but can not equal the precision and accuracy obtained by using the actual sunspot to draw the dial on the ceiling. I still think that the easiest and best way to draw a ceiling dial is to first permanently install and mount the mirror to its support structure, and then mark the center of the sunspot on the ceiling at different times, and connect the dots. John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com>
