Hello Anselmo, The times of sunrise and sunset can be easily determined on a vertical declining dial that has declination lines. The horizontal line from the base of the gnomon is the horizon line. The intersection of the declination line and the horizon line shows the time of sunrise or set. This is of limited use on south facing dials as the scale of the gnomon and resulting declination lines is usually to great to show much more than the winter solstice. Declining dials, east for sunrise and west for sunset show the times well. You also get a sense of the azimuth as this is the line from the intersection point through the tip of the gnomon to the distant horizon. This may seem obvious but it is not. The vertical declining dial on my house shows hour lines above the horizon line. I did not realize the problem until I checked the design using Fir's program. It clearly showed the horizon line and sunset times.
I do not know if this answers your question. It addresses sunrise and sunset times but does not look at insolation times, how long the sun is on the dial. Roger Bailey Walking Shadow Designs N 51 W 115 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Anselmo Pérez Serrada Sent: January 12, 2002 3:56 PM To: Sundial, Mailinglist; fer j. de vries Subject: Re: Seasonal Sunrise Marker Fer, I have read in Rafael Soler Gaya's book that you can rotate these circles (or the approximation by straight lines) you have drawn so that they can tell you as well the sunrise and sunset hours for any vertical declining dial... The problem he says that incidentally in a very brief paragraph and perhaps I misunderstood his words. Do you know if that is true? Cheers, Anselmo
