Pete Swanstrom wrote: > snip... > I do still have one big question that I wish to resolve, which pertains > to my analemmic equatorial sundial. The question is, how long will it be > before the changing analemma renders my current analemmic gnomon > inaccurate? (Say until either the date positions on the gnomon have > shifted by 1/4 day or more, or the EoT for some date has changed by over > 15 seconds.) > > Thanks again! Pete Swanstrom. >
This already happens within each 4 year period. The begin of the seasons shift about 5h50m each year. In 3 years this is about 17.5 hours, more then half a day, and in 4 years it should be nearly a day which is corrected by adding 1 day in our calendar. Than we start again. But in the 4 year we jump about 3 quarters of an hour to much. After 100 year this gives a shift of about 0.22 day. After 400 year this should be 0.88 day but than we leave the extra day so the difference remains to about 0.12 day. After about 3200 years we need the extra day again. By this reason also the EoT changes more than 15 seconds at some days in a 4 years period, only due to the length of the year which isn't 365 days exactly. So not only long terms are involved, also short terms. But thanks for the discussion on this list. It's all very interesting to read. Fer de Vries, Netherlands.
