You got it... Luke
Arthur Carlson wrote: > I wrote: > > > > ... I think > > > the processes which change the eccentricity and obliquity of the > > > Earth's orbit work on a much slower time scale than the precession of > > > the equinoxes, so that we can still use the same Equation of Time > > > 13,000 years from now. Does anybody know for sure about this? > > Luke Coletti <[EMAIL PROTECTED]> replied: > > > You are right regarding the relative small changes in the values of > > Obliquity and Eccentricity over the period of a precession cycle. However, > > it > > is the phase relationship of the two effects and not their values that play > > the > > dominant role in the variation of the Equation of Time over this period. The > > Analemma will indeed look considerably different 13,000 years from now. > > My mistake. The magnitude of the obliquity and eccentricity change > very, very slowly, but the phase is determined by the precession of > the perihelion (also very, very slow) and the precession of the > equinoxes, with the 25,860 year period we are discussing here. > Putting it another way, dialists (not only those using astrolabes) do > care about the stars because they care about the perihelion, which is > fixed relative to the stars. > > The Millennium Clock will either need to calculate the changing > Equation of Time, or else average its sighting of the sun over several > years, which I presume to be more difficult. I would anyway rather > see the clock designed for the astronomically significant cycle of > 25,860 years than for a numerological cycle of 10,000 years. If the > mechanism of the clock inherently contains the precession period, that > is one more reason to make the display correspond. The 10,000 time > frame was chosen, among other reasons, because that is the length of > time since the development of agriculture and technology. On the > other hand, there were some damn good painters active 25,860 years > ago. > > Art Carlson
