On Tue, 04 Jun 2013 22:52:47 +0200, "Paul B. Andersen"
wrote:

On 04.06.2013 12:20, Henry Wilson DSc. wrote:

What amazes me is that nobody ever discusses why planet Mercury precesses at
all. How many different factors are responsible for planetary precession in
general?

What doesn't amaze me is your ignorance.

The main reason for the precession of the perihelion of Mercury
(NOT the precession of Mercury) has been known for centuries;
it is simply the tug from all the planets in the Solar system.
Relativity hasn't changed that.

Maybe they all got it wrong.
In the frame of mercury, all the planets move in ellipses that appear to be
precessing because of their own orbital motion. Right?
Why should that have a nett force on Mercury over a long period of time?

Also, what effect would a finite speed of gravity have on the overall picture?

According to Newton, the precession should be 5557 arc seconds
per century. However, when the precession of the perihelion
of Mercury's was measured by Le Verrier in 1856, he found that
Newton's prediction was not exactly right, it was 38" per century
too small. Later more precise measurements have shown that the
precession of the perihelion of Mercury is 5600 arc seconds
per century, so the discrepancy is 43" per century. This is called
the anomalous precession of the perihelion of Mercury, and its
cause has indeed been discussed since Le Verries's time.
(Ever heard of the planet Vulcan?)
It is this anomalous precession that is explained by GR.
GR predicts 43" per century in addition to the tug from the planets.

Only after Einstein added the infamous factor of 2 after he found his original
prediction was wrong.

There are other factors as well, the oblateness of the Sun is one,
but this effect is minute.

The effect of the speed of gravity isn 't.

And of course the orbits of all the planets in the solar system
are precessing by the same reasons.

Something doesn't add up. I don't see that the fact that all planets are
orbiting in the same sense should cause precession. Where is the evidence of a
one way 'tug'? If some are pulled one way, others must be pulled the other
way.

Henry Wilson DSc.