Thank you Chris for that nice amplification of my comments. My sundial has figure eight hour lines. The problem is where does one place the figure eight hour lines. My sundial is a globe of the earth with longitude lines indicated every 15 degrees. The figure eight hour lines are placed on the globe at a slight displacement from the 15 degree lines. The issue is that the placement varies from year to year. I believe that the periodicity of this placement is a similar one to that in the EoT error, if not one and the same.
Am I missing something here? Dan Wenger >Daniel Wegner ([EMAIL PROTECTED]) is only partly correct in >saying that an analemma must have an error due to leap years. The error can >be avoided. > >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. >If an EoT table is drawn graphically to allow a sundial reading to be >converted to mean time, then this too must have an error with the same 4 and >400 year cycles. > >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. > >By the way, if you are ever making a circular date scale - to calibrate a >declination scale, for instance - you should divide it into 365.25 and make >February 29th be just the .25. This is the best simple way to allow for one >February 29th every four years. > > >Chris Lusby Taylor > >======================================================= >Email: [EMAIL PROTECTED] > (Formerly [EMAIL PROTECTED]) >======================================================= Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
