Chris Lusby Taylor <[EMAIL PROTECTED]> writes: > Another approach would be to have a ring for each value of the > EoT. That turns the figure-of-eight hour lines into a > figure-of-infinity date line. Having found today's date one follows > the ring it's on to read the mean time directly from the shadow. > This should be easy to use. The hour lines could be almost straight.
This would work with an axial gnomon, where the direction of the shadow does not depend directly on the declination. I haven't done the math(s) in detail, but I don't think it would work with a vertical gnomon because the azimuth of the sun depends not only on the hour angle (Equation of Time) but also on the declination. In other words, the direction of the shadow at a particular time depends on the date for two reasons (EoT and declination) with different dependences on the date. Consequently, it would be a great exception if two dates could share the same time markers. Cheers, Art
