Arthur Carlson wrote:
> I meant effectively fixed, in the sense that it hardly moves on the
> 10,000 year time scale we are talking about. Is that right?
No, to see this lets consider the change in Perihelion over a short
period. The URL below shows the times of Perihelion from 1992 -2005:
http://aa.usno.navy.mil/AA/data/docs/EarthSeasons.html
The variations listed are mainly due to the perturbing effects of the
Moon as the barycentric point of the Earth/Moon system changes, see J.
Meeus, Mathematical Astronomy Morsels, chap 27.
Arthur Carlson also wrote:
> For the Earth isn't the perturbation due to Jupiter the only significant
> cause?
No, the maximum perturbing effect of Venus on Earth's heliocentric
longitude at 12 arc-secs is almost as large as the maximum caused by
Jupiter at 13 arc-secs. The total maximum caused by the significant
planets is 31 arc-secs approx.15 minutes of time.
I have a graph (in digital form) of the long term change of Perihelion
(which is very non-linear) somewhere, when I find it I'll send it along.
However, I think the question of whether Perihelion can be considered
fixed or not should be apparent.
Best Regards,
Luke Coletti
