Hello all: My new dial design will have the customary seven declination lines indicating the cusp of each month (the ascent and descent of the sun between the solstices). Rohr (pg. 84) lists these dates as the 21st of each month, however, depending on the year, this date can fall between the 20th and the 23rd of some months (Rohr pg. 97). The Shadows sundial generator lists its preselected zodiacal declination lines at: 0, +/- 11* 29', +/- 20* 20', +/- 23* 27'. Does anybody know to which dates and year the Shadows program refers?
In labeling these lines on the dial, should I use the 21st for each month, or should I use different cusp dates for an average year like 1998 (half way between two leap years)? Which is customary? For example, ZONWLAK permits you to pick any any year and any declination, so if I use this program, should I pick 1998 as an average year and use the declinations for the 21st of each month, or should I use the correct declinations? ie. the autumnal equinox in 1998 was on Sept. 23, not Sept 21. I'm sure that you have probably discussed this problem before, but if you could repeat the correct answer again, I'd be most grateful. Thanks, John Carmichael p.s. I think it would be easier for the general non-dialing public to understand labeling on the 21st of each month.
