Hello all: I have been working on the design of my new double duty 40" horiz. sundial which will use the same cable gnomon as my current sundials (see website) but will also include a brass vertical gnomon/nodus for date, solar azimuth & altitude and analemmatic noon mark. At first I was thinking of locating the vertical gnomon/nodus at the dial's center, with the cable attached to its foot which would place the equinoctial line north of center. But then I noticed that if I place the vertical gnomon south of center, at exactly the right distance, that the equinoctial dec. line could be made to pass through the dial's center. This arrangement seems to be the perfect solution to several goals:
1. By centering the equinox line over the center of the dial, all the lines used with the vertical gnomon are nicely centered in the middle of the dial. (currently, I use this non-functional part of the dial for artwork) 2. By placing the vertical gnomon SOUTH of center, I am able to use a taller gnomon (about 10") which produces greater spacing between the summer and winter solstice lines and a larger analemma (about 18" at 12 pm). Because the vertical gnomon/nodus lines are larger, precision is greatly increased. 3. For telling time, a vertical gnomon, by itself is not as precise as a polar axis style, especially around noon in the summer because there is severe time line compression at this time. But for declination readings, a vertical gnomon is better than a nodus located on a polar axis style because it is taller. Using both a vertical gnomon/nodus with its own declination lines and a seperate polar axis style ( the cable) with its own hour lines gives the best of both worlds: precise dates and precise time. Any thoughts on my thoughts? gracias, John Carmichael http://www.azstarnet.com/~pappas
