Chris Thank you for your comments that amplifies on your email of 17 Feb 99.
I am not convinced that your comments are true. My computation of the curve on my sundial involved a determination of the geographical lat. and long. of the sun versus the long. of the mean sun. My recollection is that that relationship involved a choice of epoch and that this choice, if altered, would alter the placement of the curve, although by only a small amount over a four year period. I will take another look at the calculation and perhaps post it here for others to comment on. Would you be willing to substantiate your statement? Are there others who perhaps can give the/a relationship between the suns geographical position versus the geographical long. of the mean sun? Dan Wenger >Daniel Lee Wenger <[EMAIL PROTECTED]> writes: > >> On my globe the significance of the analemma is apparent. Each analemma >> represents the geographical >> position of the sun at mean time 6, 7, 8, 9, etc. for each day of the year. >> In fact the geographical >> postions of the sun at those mean time hours would be a collection of 365 >> dots but the analemma >> is interpolated to generate a semi continuous curve. Since the set of dots >> that would be generated during the following year would be slightly >> different the curve used represents some sort of average >> of the dots over a four year period. > >The set of dots that would be generated during the following year would lie >on the same curve. The reason the dots are not in the same places is that >the year is not a whole number of days long. The curve is not an average >over a four year period. If you were to draw four years' curves separately, >you would see that the curves are identical, but the points used to plot >them are not. The curves are the graph of Equation of Time against >declination, both of which are functions of the solar longitude. The >particular values of solar longitude at, say, noon every day in 1999 are >different from those in 2000, but the analemma points lie on exactly the >same curve (ignoring only very long-term drift). >To use straight lines as an illustration, the points (1,100) and (6,105) lie >on the same line as the points (2,101) and (7,106) or the points (3,102) and >(8,107) or the points (4,103) and (9,108). > > >Chris Lusby Taylor > >Email: [EMAIL PROTECTED] > (Formerly [EMAIL PROTECTED]) Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
