Dave Bell wrote: > On Mon, 22 Oct 2001, Chris Lusby Taylor wrote: > > > Can anyone help me, please, with understanding a sundial in Bremen shown in > > Frans's 'inverted' armillary sphere section. (See < > > http://www.hs-bremen.de/planetarium/astroinfo/sonnenuhren/digitalk.htm >). > <snip>
> >. I cannot see why a curved dial should work. > The best rationale I can see for the curved dialplate is to keep the > shadow surface at a constant distance from the image-forming holes in the > ring. With the pivoting dialplate, you also get the essence of a curve in > the East-West plane, as well. By manually adjusting the plate so the > perpendicular post is in the Sun plane, you have a "slice" of a > hemispherical dial. > > > The biggest contradiction I cannot resolve in my mind relates to the > > analemma. <snip>. > > I think this is the same answer? > > Dave Bell > 37.3N 122W Hi Dave, Thanks for the explanation. I hadn't realised that the curved dial plate was pivoted and should be rotated to face the sun. I thought it was fixed. I'm afraid my German isn't up to reading the text, which no doubt explained this. If you're going to pivot the dial plate to face the sun, its curvature doesn't affect timekeeping. I can imagine that having the dial at a constant distance from the ring gives a clearer image. I now realise that the dial is convex. I had thought it was concave - the pictures can be 'read' either way! Regards Chris 51.4N, 1.3W Content-Type: text/x-vcard; charset=us-ascii; name="chris.lusby.taylor.vcf" Content-Transfer-Encoding: 7bit Content-Description: Card for Chris Lusby Taylor Content-Disposition: attachment; filename="chris.lusby.taylor.vcf" Attachment converted: Macintosh HD:chris.lusby.taylor.vcf (TEXT/ttxt) (00032334)
