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From: tomyee3@gmail.com (ProkaryoticCaspaseHomolog)
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 01:12:01 +0000
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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.)
> 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.

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.