Gianni, You wrote:
> Because of these changes of the EOT from one year to the other it is wrong, > in my > opinion, to use values very precise in calculating sundials. They may be > useful to find the exact istant of the noon in a given day, etc. > I don't fully agree with your arguments. If drawing the EoT curves ( analemmas ) on a sundial try values with a reasonable high accuracy. But use the combination sun's declination and EoT. These combinations don't hardly change in a man's life. Also declination lines on a sundial are accurate for such a period and so far you may use the values of any year. I think that's even better then using average values for a leap year period. Problems occur if date lines are drawn. The relation between date on one hand and sun's declination / EoT on the other hand changes in the leap year period as you wrote. The result is that in fact date lines aren't precize on a dial but declination lines are. Declination marks on an EoT curve would be better then date marks for accuracy, however, many times I would prefer date marks or datelines. A dial isn't a precision instrument in most of the times. I fully agree with you writing:: They may be useful to find the exact instant of the noon in a given day. But than the correct values for the running year have to be used because you also use the date. 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: "Gianni Ferrari" <[EMAIL PROTECTED]> To: "SUNDIAL MAILING LIST" <[email protected]> Sent: Monday, June 16, 2003 6:44 PM Subject: Re: Precise EOT Program - Comments and a correction > > Hank, > > some years ago also I have obtained the Fourier approximation of the EOT > from its MEAN values on a 48 year period (from 2000 to 2047) ( I published > it in 2000) > > The coefficients that I have found are practically equal to those found by > you and precisely: > > t = 2 * pi * (j - 1) / 365.2421897 > EOT = 0 + > + 7.3656 * Cos(t + 1.5113) _ > + 9.9158 * Cos(2 * t + 1.9574) _ > + 0.3060 * Cos(3 * t + 1.8347) _ > + 0.2027 * Cos(4 * t + 2.3213)_ > > Where j = N-1 and N = number of the day in the year (32 for February the > 1st) > > I have also calculated the difference ( true exact value - mean value from > formula ) in every day of the perod (17532 days) and I have found a maximum > error less than 18 sec. > > The values (exact) of the EOT changes from one year to the other as in the > follwing example. > > EOT calculated on December 25 at noon in Greenwich : > > > DAY Time Eq. > > DEC 25 2003 Th - 6.90 sec > > DEC 25 2004 Sa +16.74 > > DEC 25 2005 Su + 8.64 > > DEC 25 2006 Mo + 1.68 > > DEC 25 2007 Tu - 5.82 > > DEC 25 2008 Th +15.72 > > DEC 25 2009 Fr + 9.00 > > DEC 25 2010 Sa + 0.84 > > > The mean value = 6.54 sec. On December 26 the mean value = 36.2 sec > > Because of these changes of the EOT from one year to the other it is wrong, > in my > opinion, to use values very precise in calculating sundials. They may be > useful to find the exact istant of the noon in a given day, etc. > > A regard > > Gianni Ferrari > > > > P.S. - The EOT is non changed from the atmospheric refraction > > > > > > > > > > - > -
