Dear Siegfried, You ask:
> I am confused ... about your sundial design / drawing Most sundials have a polar-oriented gnomon, and the shadow directly indicates the hour-angle of the sun. The hour lines (and other features) on such a sundial are a *gnomonic* projection of part of the local celestial sphere. 'My' design (which is many centuries old!) requires a vertical gnomon, and the shadow directly shows the azimuth of the sun (its direction). The relationship between azimuth and hour-angle varies according to the time of year so I include seven circular arcs for different times of year. The extreme arcs are for the winter and summer solstice. The central arc is for the equinoxes. This is one example of an azimuth sundial. There are many possibilities. In the design I attached, I use a *stereographic* projection of the local celestial sphere. The centre of the design corresponds to the local zenith and the outermost circle corresponds to the horizon. This design can therefore show the entire heliodrome. A gnomonic projection can show only part of it. My design is intended for 52.2 N and your latitude is about 49 N. If you print out the design it will work approximately. If you can fix a day-trip to Hanover it will work better! One great advantage of this design is that you can cut it in half and rearrange it. I give a full description in the book 'Sundials - Cutting Time' which you can see at: www.kindersleyworkshop.co.uk/shop The stereographic projection is one of the greatest gnomonic inventions. You don't have to have the zenith in the centre. On astrolabes, the centre is a projection of the north celestial pole. Frank Frank King Cambridge, U.K.
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