On Mon, 3 Jun 1996, Fer J. de Vries wrote: > On a flat plane the following lines also will be straight: > -azimuth > -astrological houses (system Regiomontanus) > -italian hours > -babylonic hours > -siderial hours > -ascendants and descendants > -the declination line for declination = 0 (equinoxes)
They all have in common that they are generated by a gnomonic projection of a 'grand circle'. The gnomonic projection transforms a 'grand circle' into a straight line. E.g. the italian and babylonic hours are the projections of horizons which are 'grand circles'. I'm not sure if I have found the correct translation for 'Grosskreis', the german word for the intersection circle of a sphere with a plane containing the center of the sphere. Please let me know if the word isn't correct. - Daniel Roth, Arbeitskreis Sonnenuhren, Germany
