> Mac Oglesby recently asked: > > > >John Close has posted this message on the NASS Message Board: > > > >"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. > > As a Polar dial with an 'Oliver' type analemmical 'centrebody' is > effectively a Schmoyer 'Sunquest' with the hour arc flattened out into a > plate I don't seem to see any problem with this idea. Of course the > Oliver device is symmetrical so the meantime correction would be only a > close approximation. Of course it will suffer from the same problem all > polar dials demonstrate viz. a shadow of increasing fuzziness away from > Noon and problems with the early/late hours. > > Tony Moss > > P.S. Apologies for the delayed response but other problems have had my > undivided attention recently. > - > Pardon my ignorance, Tony, but could you please remind me/us what the Oliver device is.
My initial thought was that the objective - a mean time polar dial without analemma-shaped hour lines - was impossible due to the varying distance from the gnomon to different parts of the dial. The Schmoyer type equatorial works because the same section of the gnomon is used all day long. Is the Oliver device immune to this problem? I cannot imagine any shape that would be. While it is true that a polar dial has increased fuzziness away from noon, this is exactly compensated by the faster rate at which the shadow moves across the dial. So the fuzziness is plus or minus two minutes at all times. Chris Lusby Taylor Newbury 51.4N 1.3W -
