Hi Anselmo and others, In your last message you mentioned other factors, like atmospheric, refraction that might affect precision when setting or reading a sundial.
I've often wondered if there is a best time of day to set a sundial using the "Time method" (as opposed to the compass, the Polaris, the GPS and plumbob shadow methods). I'm thinking that the best time of day to precisely set and/or read a horizontal sundial would be at mid-morning and mid-afternoon (those times that are halfway between sunrise and apparent noon and apparent noon and sunset). These setting & reading times would avoid the early morning and late afternoon affects of maximum atmospheric refraction and would also avoid the compressed hourline markings that are close together at noon which make time estimation more difficult. Does anybody agree with my theory? Is there a best time for setting sundials? Thanks John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> ----- Original Message ----- From: "Anselmo Pérez Serrada" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, June 15, 2003 9:59 PM Subject: Re: Precise EOT Program - Comments and a correction > Hank de Wit wrote: > > > However, the method of simple differences introduce a 12 hour phase > > error so we would be better off producing the differential dEOT/dt. As > > the fourier approximation is linear this can be done with high school > > calculus. I've included the differential function below. Luckily this > > produces the same numerical result (to two dec. places) as before > > except the date is now 23.0UTC Dec (as expected from the phase argument). > > Beware! The derivative of an approximating function need not be the > approximation of the derivative of the real function. > > Besides, we must take into account that all algorithms to calculate the > EoT aren't very robust and are only accurate for > a more or less narrow span of time. No algorithm would be able to > calculate the EoT on the day when Ramses II was > born, for instance. > > And finally, if John or somebody else wants to work in the range of 10 > sec they'll have then to take into account other > difficult to calculate factors like the atmospheric reffraction (the > formulae we know are all rough approximations). > > Best regards, > > Anselmo Perez Serrada > > - > -
