Re: Orbital precession w/o GR

"JMA" <NOSPAM@xxxxxxxxx> wrote in news:5r9a6hF13l56tU1@xxxxxxxxxxxxxxxxxx:

My [not so clear] point was that they mean [to paraphrase slightly] is
that "the precession of mercury is the slow shift of the point of
nearest approach to the sun along the orbital plane," whatever the
cause of said drift.

After taking into account the gravitational effects of all the planets,
there was still some 'precession' left over. They first attributed it
to a small [as yet to be observed] planet inside mercury's orbit, but
that theory was rejected because such an orbit would not be stable.

GR came to the rescue and explained the drift.

So far I'm trying to figure out the problem based on Newton.

Then look at how precession of the equinoxes works.


When you say, "the precession of mercury is the slow shift of the
point of nearest approach to the sun along the orbital plane" how
does that point shift.
1 - The point becomes closer, or far away, from the sun within
the plane of the orbit.

NOT what I am talking about. Not to say that this might not happen, but
this is NOT precession.

2 - The distance to the Sun is always the same, but the point
moves in a plane orthogonal of the orbit plane.
(The distance to the Sun is always the same since rotation occurs
along a line that includes the Sun and is orthogonal to the line
defined by the perihelion-sun-aphelion.)

The oval 'pictures' of the 'orbit' do not exactly overlap [with respect to
'the fixed stars' and a heliocentric frame of reference]

Keep in mind the FACT that the rotation of the SUN around its axis and
the revolution of the sun around the galactic center and the drag from
each passing planet has an effect on that ellipse.

No specific constant 'torque' need be supplied, but the planet 'Vulcan'
would have supplied such a torque if Vulcan existed.

Torque needs to be orthogonal to the plane of the orbit.

That is your understanding.

'Precession' can be used as a model by assuming a rigid body rotating and
calculating the [averaged] impulsive torques that each planet exerts on
every other body in the solar system.


That is, the vector torque is in the plane of the orbit.

The model is a rotating rigid body. It has angular momentum.
Periodic small taps provide something which can be modeled as a
constant 'torque'.

I guess people say it is precession because they don't know
what precession is and it's a sound name.

If I do not understand why a particular word is used, that does not imply
that those that use the word are ignorant.

Astronomers use the word because the earth precesses just like a top.

'People' say it is precession because the MODEL of a rotatin rigid body
precesses. The word is correct.


Mercury's perihelion advance doesn't look like precession.

That depends on what is meant by 'look like'.

When you use the right math to average those periodic small taps via the
mechanism of their influence on the angular momentum of a rotating body
that is orbiting a very massive rotating body, precession is the
correct word to use.

Even so, all books and every drawings show a precession
like motion that is constant and requires constant torque.

The rotation of the flywheel in your car does NOT require a constant
force. It is sufficient that small explosions provide energy. Inertia
averages those pulses.

Newton is necessary for understanding what is going on with Mercury.

Newton's physics [as modified by Einstein] AND Newton's invention that
we call 'calculus', allow the handling of those 'small taps', delivered by
the orbiting planets, so that we need not have a 'constant torque' to get
precession.

Eric and Androcles [I hate to cite Androcles. I no longer read his posts
because of HOW he says things and the fact that reading his rants is
usually a waste of time, but you quoted him. I ALSO don't like how Eric
often says things but his clue to noise content is much higher than
Androcles] have each given you some very good advice and clues.


--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+spr@xxxxxxxxxxxxxxxxxxxx remove ch100-5 to avoid spam trap
.

Relevant Pages

  • Re: Orbital precession w/o GR
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  • Re: Orbital precession w/o GR
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