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--- Begin Message ---I think I must be missing something here. I cannot quite wrap my brain around what we would be trying to accomplish with a longitude adjustment. A horizontal garden variety dial should tell apparent local solar time as long as it is correctly designed and the gnomon is pointing at the north celestial pole. It can be moved to a new location and will continue to tell apparent local solar time as long as the whole thing is tilted so that it is at the latitude it was designed for and positioned so that the gnomon continues to point to the north celestial pole. Now, If such a dial were to be tilted on its other axis so that it corresponds to the original longitude then I think it would tell local solar time at the original longitude. This would appear to be wrong since it would not correspond to either local solar time or local civil time. AFAIK, the only way longitude comes into play in the design would be to make the dial conform more closely to civil time (leaving aside the equation of time) for example if the dial is located near the edge of the time zone. AFAIK the only way to do this is to shift the dial plate around the vertical axis originating at the bottom end of the gnomon so that noon is no longer lined up with the gnomon and east west are no longer at right angles to the gnomon. If such a dial were relocated then it would need some kind of longitude adjustment but would it not then tell something approximating civil time at its old location rather than the new one? Is this wrong? Is it possible to make a local longitude adjustment by tilting the whole thing on its polar axis? My spherical trig is almost nonexistent so I am trying to imagine all this visually and cannot quite see how it would work. It seems to me that an east-west wedge would throw the gnomon off its polar axis. Jack Aubert From: sundial <sundial-boun...@uni-koeln.de> On Behalf Of Steve Lelievre Sent: Monday, April 3, 2023 7:47 PM To: Rod Wall <rodwall1...@gmail.com>; kool...@dickkoolish.com Cc: 'Sundial sundiallist' <sundial@uni-koeln.de> Subject: Re: Adjusting dial to new location Hi, Roderick, My home internet connection is still non-functional so I can't fix it yet, but it does seem that I will have to add an extra test to handle southern hemisphere locations and reducing latitudes. Actually, I originally had a southern hemisphere check in there but took it out after convincing myself the same frame of reference (x axis east, y axis north, z up) applied to the spherical trigonometry irrespective of hemisphere. Ho hum. Steve On 2023-04-03 6:45 a.m., Rod Wall wrote: Hi Steve, For both examples below with all sundials at the same Longitude. The instructions indicate: Place the wedge-sundial assembly on a horizontal surface in a nice sunny location. Start with the higher end of the wedge to the north and the sides aligned on a north-south line and the sharp edge should be on an east-west line. Example 1: If you have a sundial that was designed for Latitude -20 deg. And relocate it at Latitude -50 deg. Would you start with the higher end of the 30 deg wedge to the North. Or would it be to the South? ***** Example 2: If you have a sundial that was designed for Latitude 50 deg. And relocate it at 20 deg. Would you start with the higher end of the 30 deg wedge to the North. Or would it be to the South? ***** Please correct me if I am wrong. I think that both examples would be to the South. Roderick.
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