not only altitude dials, but azimuth dials also. I have a chapter in Illustrating More Shadows showing the portability and rules for portability of both dial types, from the equator to the pole, and the correlation with calendar curves on an hour angle dial.
The DeltaCAD macros for the Shepherd and the winged azimuth dial's both animate over latitude, and it interesting to see the evolution fro the equator to the pole, and in the case of the azimuth dial, even more fun when given a longitude correction. Simon --- Edley McKnight <[EMAIL PROTECTED]> wrote: > Hi Duane, Roger, and all, > > A true equatorial mount is truly fine if you have > one, A simple hinge mounted > in parallel with the earth's axis at some point > below the horizontal surface, > allowing the dial to tip a little one way or the > other will allow adjusting for both > Longitude and the Equation of Time. One could > consider the sundial to be a > slightly slow or fast clock and set it daily for the > correct time, like any other > clock. (even daylight saving's time if the tilt is > large enough) Mounting an > east west hinge below that would allow adjusting for > errors in Latitude as > well. Setting up such a table is a fun thing to > test various designs or sundials > found. I call it an "Latitude/Longitude table". > > BTW, Even Pillar or Shepherd's dials made for other > places seem to work > just fine locally when rotated on such a table, set > for the correct Lat/Long > rather than dangled by their cords. Has anyone else > observed this? > > I still like Hendrik Hollander's cone gnomon design > the best currently. > > Enjoy the Light! > > Edley McKnight > > > 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 > > > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
