Chris Lusby's post is instructive and I'd like to learn more. Chris Lusby wrote:
> It is true that tables of the Equation of Time are slightly inaccurate > > because they take a mean value for the solar longitude on a named date > (such > as February 17th), whereas the 4 year and 400 year cycles should be > allowed-for to be totally accurate. Fortunately for us, the peak error > is > less in the next few years than at any other time in the 400 year > cycle. How > convenient. The worst case is in 1903+400n and 2096+400n, when the > longitude > is 7/8 of a day different from its mean value. But even 7/8 of a day > accounts for less than 30 seconds of EoT, so still allows a sundial to > be > less than a minute out. Around the year 2000, the worst case is half > this - > about 14 seconds. Where do the 1903 and 2096 come from? Am I correct in assuming that ALL of the EoT discrepancy above comes from the (longitude-mean day) delta? > But if the sundial is marked with figure-of-eight hour lines, then > there > need be no such error, since the sun's declination and longitude are > related > by geometry, not by what we call the date. Even if we lost another 11 > days > in a calendar reform (I am from England), such a sundial would > continue to > read correct mean time. Therefore, I suggest that this is a purer and > altogether more satisfactory solution than an EoT table or figure. > Except > for the little point that the EoT changes rather a lot, and the > longitude > does not, at the solstices. Pity. I often see the figure-of-eight hour lines and don't understand why just one along the noon hour line isn't used. Is it only the practical matter that the observer isn't "there" at noon when he/she is observing at say 3pm? Or can the noon observation NOT be used to "calibrate" the observations for the rest of the day, at least? Thanks for your help t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<((((*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
