Hi Jim, Declination lines will last for a very long time, at least if: - the dial was correct constructed - the orientation of the dial isn't changed in the course of ages - the dial isn't restored in a wrong way and so on.
Date lines are more difficult. Except for the solstices a dateline is at least one time wrong in a year because it will be used two times with the sun's declination of the same value. In other words, for each date line two dates are true. For a certain date the sun's declination will change each year in a leap year period but also over a long period. So calculate for a date of your choice the sun's declination for e.g. 1600, 1700, ..... 2100 to see the change. It will depend on the date you have choosen. For a zodiacal calendar however, the lines wll last for a longer time. The zodiacal calendar isn't in phase with the real situation but with the longitude of the sun and by that with the sun's declination. In fact it are declination lines. Also you have to look to the change in the obliquity of the earth axis. Well, there are many aspects to think about but in dayly dialling we may forget a lot of them. Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring mailto:[EMAIL PROTECTED] http://www.de-zonnewijzerkring.nl Home mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/index-fer.htm Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: "J.Tallman" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, June 16, 2003 9:34 PM Subject: Declination line precision over the years > Hello all, > > This recent discussion has me wondering about some of the old dials in > Europe, and the declination lines on some of them. How well has the > precision of these lines held up over time? > > Just for general discussion purposes, if I put a declination line for a > specific date on one of my sundials, how long could I expect it to be > accurate? > > > Best Wishes, > > Jim Tallman > > > - > -
