Hi, I haven't seen any reply to the John Close / Mac question. Did I miss something? What's the verdict?
For my part, I can see that it would be possible to construct a 2D shape (approximately oval), which when set in equatorial plane, would cast a shadow giving a certain EoT adjustment - you would read off the time from the leading edge of the shadow of the oval. Next day, the EoT is different so the oval is a different size. You would need to stack a parallel set of these ovals to form a "cylinder" along the polar axis, and have something to indicate which one to use for a given day. But on the second day, the declination is different as well. A sun ray trying to touch the edge of the smaller oval will be blocked by the larger one adjacent to it (or vice versa). So the thing wouldn't work. To get round the latter problem, you would have to set the plane of each day's oval according to the declination of the sun on that day. The ovals are not quite the same shape as before, but the principle is the same. You would end up with a gnomon which was a bit like a bull's horn - curved and changing in thickness along its length (according to EoT). You would have to swap the gnomon for another when the declination changes from decreasing to increasing. Your timescale would be an East-West line instead of a face with a set of hourlines, so it wouldn't handle morning and evening well (a bit like a polar dial) but I think it would work.... Steve > "Does anyone have any ideas for a Polar Dial which allows for an > Equation of Time adjustment. I would not like analemma shaped hour > lines as I think this would detract from the simplicity and > minimalistic quality of a Polar Dial. I am told an analemma shaped > gnomon for a polar dial would be hideously complicated and probably > not work . Any ideas anyone? John Close" > > John has discussed this problem with several members of this list, > including me, Bill Gottesman, John Davis, and Pete Swanstrom. Some of > us think that a 3-D gnomon could be designed for use with straight > hour lines to correct for EoT, and some are skeptical. > Please share your comments and suggestions. > P.S. Since I do not know if John Close is a member of this List, > please cc to him. -
