Arthur,
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.
Mathematical Astronomy Morsels by J. Meeus has a chapter (although its a small
one) devoted to the EoT and its variation.
http://www.willbell.com/math/mc16.htm
Best Regards,
Luke Coletti
Arthur Carlson wrote:
> "Sonderegger" <[EMAIL PROTECTED]> writes:
>
> > I think in the northern hemisphere summer is always in July, because the
> > beginning of spring is here always when then sun crosses declination of 0
> > degree from south to north (= crossing the ecliptic). The places of the
> > stars on then sky will change in this 13000 years.
>
> Right. The question is not whether summer will be in July, but
> whether July will be in summer. That only depends on how you choose
> your calendar system. The Gregorian calendar reform was an effort to
> keep July in the summer. The precession is a physical process, which
> does not depend on our calendars. What it does is change the
> constellations that are visible at night in July. Since we don't use
> the stars for sundials, it won't make any difference. What will
> matter is the Equation of Time, as mentioned by Luke Coletti. 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?
>
> Art Carlson
