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From: "Paul.B.Andersen" <relativity@paulba.no>
Newsgroups: sci.physics.relativity
Subject: Re: Weakness in the results of the three tests of GR shown in rhe
 lasr century,.
Date: Thu, 31 Oct 2024 10:08:38 +0100
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Den 31.10.2024 02:12, skrev ProkaryoticCaspaseHomolog:
> On Wed, 30 Oct 2024 21:45:10 +0000, Paul.B.Andersen wrote:
> 
>> Den 30.10.2024 01:30, skrev rhertz:
>>> On Tue, 29 Oct 2024 21:35:06 +0000, LaurenceClarkCrossen wrote:
>>>
>>>> Mr. Hertz: Perhaps this source would be interesting: "Hipparcos did not
>>>> measure directly the light bending" = Serret.
>>>
>>> Of course IT DID NOT!
>>>
>>> The MAIN objective of HIPPARCOS was to measure the RELATIVE POSITION AND
>>> LATERAL MOTION of more than 100,000 stars with respect TO EACH OTHER,
>>> besides its  brightness and colors.
>>
>> Right.
>> The point with measuring the positions of the stars relative to each
>> other is that neighbouring stars have the same stellar aberration,
>> so it is not necessary to compensate for. (The correction is small.)

This is poorly formulated.
Note that I said "The correction is small."
What I meant is that since the stars are close to each other
the correction is small relative to 20", and the distance between
them can be measured with better precision than if the stars were futher 
apart.

>> The angular distances between the neighbouring stars are measured
>> with a precision of ~1 mas. The sky is scanned over and over at
>> different times of the year so that the distances between
>> the same stars are measured many times.
>> Change in the distances between the stars can be caused by:
>> 1. Proper motion. (A constant angular velocity)
>> 2. Parallax. A yearly change in the position.
>> 3. Gravitational deflection of the Sun. A daily change in position.
>>
>> Post-procession of the data is obviously a formidable task.
>> But even you should be able to understand that it is possible
>> to find:
>> The position of each star.
>> The proper motion of each star.
>> The parallax of each star. (Distance.)
>> The gravitational deflection of some of the stars.
> 
> ..and their displacements due to stellar aberration. The precision of
> Hipparcos's measurements were such that stars even a fraction of a
> degree different in declination would follow measurably different
> Bradley ellipses (or rather, overlapping Bradley ellipses from the
> spacecraft's orbit around the Sun and its orbit around the Earth.)
> 
> The global displacements due to stellar aberration and gravitational
> deflection, and the individual displacements due to parallax and
> proper motion all needed to be taken in account.
> 
> Hipparcos' mission was most decidedly NOT to "prove relativity right".
> Rather, adjustments of stars' measured positions due to general
> relativistic effects were among the corrections necessary to minimize
> the residuals. Otherwise it would have been IMPOSSIBLE to combine the
> data measured over a period of years into a consistent map.
> 
> ======================================================================
> 
>> Nothing was assumed.
>> When the position of a star was known at different times of a day,
>> the difference could only be caused by gravitational deflection.
>>
>> It was _measured_, not assumed.
> 
> I would put it somewhat differently. Gravitational deflection was
> _corrected for_, otherwise the data simply wouldn't make sense.

OK.
The fact that the data only make sense when gravitational deflection
was corrected for does mean that it, in principle, would be possible
to deduce the gravitational deflection from the measured data.

But of course, the gravitational deflection is known, so it
is simpler to correct for it.

> 
> Sort of like, particle accelerators don't measure special
> relativistic effects. Rather, special relativistic effects must be
> taken into account, otherwise analysis of particle trajectories
> don't make sense.


-- 
Paul

https://paulba.no/