Why are the 'Fixed Stars' so FIXED?

Henri Wilson wrote:

How does the light know that it should adjust its speed
relative to the barycentre rather than something else?

In actual fact light only 'knows' of one object, its own
source. Theoretically the source could be the only object
in the universe. The best reference for a change in speed
is the source itself.

That is what I expected.

Since I am discussing the unification of light speed from
the star over a complete orbit, I am suggesting that its
barycentre is the most practical reference to use. It is
not the only reference one could use.

I agree. My questions were about the behavior of the light,
as you discuss next, rather than choice of reference.

How does the light determine its speed relative to the
barycentre of the system it has left?

It leaves at between c+v and c-v in the observer direction,
wrt the orbit centre. I'm saying, that in time, it unifies
to something like c wrt that centre. Don't ask me how or
why... but this seems to happen in varying amounts according
to the BaTh.

It is most astonishing. Light from the star adjusts its
speed relative to something with which it has no connection.

If the light came only from the far side of the orbit,
would it unify relative to the mean radial speed during
that half-orbit, instead of unifying relative to the mean
radial speed over the full orbit?

I presume it unifies to the mean, rather than the median.
Is that correct?

Would light leaving the Moon toward a distant viewer unify
its speed to c relative to the Earth-Moon barycentre or to
the Moon-Sun barycentre?

For a three body system, The radial velocity would be
something like c+Acos(xt)+Bcos(yt).

The max amd min are c+A+B and c-A-B.

That seems reasonable.

So I presume there would be two separate unification
processes occuring simultaneously at different rates.
The A would go towards zero over relatively short
distances followed by the B over larger distances.

So light from the Moon would tend to unify relative to the
Earth-Moon barycentre, and then tend to unify relative to
the Moon-Sun barycentre.

It is a puzzle how the light could seem to know that it
was emitted from a body which is orbiting other bodies.
And it is a puzzle how the light could seem to know its
speed relative to the different barycentres.

I say this because unification rate appears to be dependent
on orbit period. Don't ask me why. There could be an entirely
different explanation as to why the hipparcos distances are
generally longer than those I need to match brightness curves.

The obvious relationship is that the shorter the orbit
period, the higher the radial speed, and thus the greater
the initial bunching effect, so the unification distance
needs to be shorter in order to prevent excessive bunching
during transit.

Leonard