Re: Precession of the equinoxes ?


<tadchem@xxxxxxxxxxx> wrote in message
news:1163192224.995180.151730@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| http://individual.utoronto.ca/kalendis/seasons.htm
| has amost informative discussion of the lengths of the seasons and why
| they vary, including some discussion of the variability of perihelion
| passage (about 1/3of the way down the apge, under "Orbital Eccentricity
| and Variation of Season Lengths"):
|
| "The intervals between Earth's passage through perihelion vary from 363
| to 367 days, which cannot be explained by interactions with other
| planets or Sun. If one considers the passages of the Earth-Moon
| barycenter through perihelion, however, this oscillation vanishes, and
| hence its cause is Moon.

That makes sense.


(See Jean Meeus' chapter 26, "The barycenter
| of the solar system" starting on page 165 and chapter 27, "On the
| passages of Earth in perihelion" starting on page 169 in "Mathematical
| Astronomy Morsels", published in 1997 by Willmann-Bell, Richmond,
| Virginia, USA). Nevertheless, there are long-term periodic variations
| in the rate of perihelion advance, which can cause successive
| perihelion cycles to differ in duration by several millennia!
| Specifically, as orbital eccentricity decreases perihelion advances
| more quickly, and conversely as orbital eccentricity increases
| perihelion advances more slowly.
|
| At the present mean rate of about 11.6 arcseconds of advancing
| heliocentric longitude motion relative to the distant stars (eastward),
| perihelion takes about 111,700 years to revolve once around Sun.


That's highly questionable.
360 degrees is 1296000 arc minutes. Divide that by 11.6
and we get 111,724 years, so the claim is 11.6 arc seconds per year.
The problem is any advance IS caused by the other planets, and
the advance of longitude of Mercury is 43 arc seconds per CENTURY
or 0.43 arc secs per year, or roughly 0.1 arc seconds per orbit, and
Mercury's orbit is much more eccentric than Earth's.

http://www.dynamical-systems.org/threebody/index.html


| At the
| same time, however, the northward equinox is precessing at the rate of
| about 50.3 arcseconds of ecliptic longitude per year (retrograde, or
| westward) or one cycle per 25,765 years, due to Earth wobbling on its
| axis like a spinning top,


Note: the advance of longitude of perihelion is also called
"precession", which can lead to confusion. And you can add nutation,
a small change in the tilt angle.
http://www.pietro.org/Astro_Util_StaticDemo/MethodsNutationVisualized.htm


| so the net effect (50.3+11.6 = 61.9
| arcseconds per year) is that perihelion takes about 20,940 years to
| revolve once relative to the northward equinox of the date, advancing
| through all of the seasons in sequence. Relativistic --- {fucking crap
deleted}

That makes the entire document suspect, Einstein omitted the other
planets entirely when he tried to explain the advance of longitude of
perihelion of Mercury.
http://www.schulphysik.de/physik/perihel/Perihel.htm
http://faculty.ifmo.ru/butikov/Projects/Collection1.html

Androcles




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