Duane, In addition to all the other comments, I'd like to mention this possibility:
An ordinary garden sundial with triangular gnomon is usually mounted on a solid pedestal with the horizontal plane fixed. If instead you place it on an "equatorial table," the sundial can wobble about an axis through the north and south celestial poles. By controlling this wobble with the seasons, you can easily counteract the equation of time and make the sundial show mean time without any mental corrections at all. Equatorial tables, or platforms, have been around since they were invented by a French genius, Adrien Poncet, and described in the January 1977 issue of Sky & Telescope, pages 64-67. The prototype that I made then is sitting on the table in front of me now, and it seems ideal for carrying a horizontal sundial! This is Poncet's concept: If a rigid body (in this case the entire sundial) is supported at three points, one acting as a fixed pivot and the other two constrained to slide on a fixed plane (that of the celestial equator), the body can only rotate around the polar axis (defined by the gnomon's shadow-casting upper edge). Since 1977, many versions of the Poncet platform have been devised and produced commercially. They tend to get more complicated when you need them to carry heavy telescopes, such as Dobsonians, and track smoothly enough for time-exposure imaging. But for a sundial Poncet's original design seems quite adequate. All you would need is a cam of the proper shape to raise or lower one end of the table (by no more than 4 degrees) to correct for the equation of time. Using a knob attached to this cam, you could dial in the current month and day and that's it! (And if you forget to reset the date for a week or two, the readings will still be quite close.) -- Roger ________________________________________ Greetings, I am a new member and have what is probably a very simplistic question. My apologies in advance. When considering a flat, fixed sundial (not an equatorial dial) it appears that to get the sundial as close as possible to watch time you set it to the latitude and then adjust it for the longitude when laying out the hour lines. Having done all that, am I right in assuming that you are still at the mercy of the Equation of Time and will need to add/subtract minutes to the dials time to equal watch time? - or is it somehow possible to adjust a flat, fixed sundial to incorporate the equation of time also? Thank you for any guidance/help you will tender. Sincerely, Duane Thomson --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
