Re: Relativistic aberration

Le 02/08/2024 à 21:49, "Paul.B.Andersen" a écrit :

 The position of the star is given as two angles and a distance.
The angles are Right ascension (RA) and Declination(DEC).
The former is equivalent to longitude and the latter to latitude.
The distance is given in Parsecs or light years.
It is of course a trivial matter to convert these three coordinates
to a Cartesian  frame of reference.
 Your system have the transit time of the light from the star
as a fourth coordinate, which is redundant because it is given
by the distance.
I didn't fail to notice that your √(x² + y² + z²) = -To⋅c.
So you could remove the To from your system.
 When it comes to the time of the observation t, it would be
very inconvenient if the stars in the star catalogues were
observed at different times given in the catalogue, so the
data are given as they would be at the same time.
The current standard is Epoch J2000 (January 1, 2000)
That means that if a star is observed at another time,
the data must be calculated to what they were at Epoch J2000.
(The angular and radial velocity will normally be known).
 Now to the real reason why this system is better than yours.
When you know the RA and DEC of the star, you know where
to point the telescope! (Corrected for stellar aberration and parallax.)
 You can now buy amateur telescopes where you can enter the RA and DEC
of an astronomical object, and the computer will know where to point
the telescope on a rotating Earth, and even track the object.
You do not have to know the distance.
 And when you observe a star, the direction of your telescope
give you the RA and DEC.

What I would like physicists to understand because it is doubly important, for the beauty of the thing, and then for the scientific truth of the equations that will result from it, is the notion of universal anisochrony, and the fact that what we believe to be an absolute present time, does not exist.
That it is only a mental idea, a complete abstraction, an empty shell.
I think it is not nice to teach children this ridiculous idea that they do not have innately, because THEY, they intuitively know the thing without being mistaken, and do not say that what they see in the sky does not exist or no longer exists, and that it belongs to the past, and that perhaps, stars that they see no longer exist.
Philosophically, theologically, artistically it is not BEAUTIFUL.
And worse, scientifically, it is false.
Now, it is preferable, you are right, to use To, which is however an abstract structure, but which places all the observers in a certain coherence that anisochrony does not allow for all the observers at the same time.
But it must be specified that it is a useful abstraction.
This is why it is necessary to note, I think (x,y,z,To,t) for any event perceived in the sky.
t being the moment when the observer perceives the event, but ALSO the moment when it actually occurs, in perfect simultaneity with the observer.
Be careful, this effect is not reciprocal; because if it is true that everything I observe in the sky is part of my present moment, of my perfect simultaneity of existence, the reverse is not true. My current existence does not exist for the whole of the observable sky and according to the distance of the stars, it will only exist for them in t = 2x / c. My present is in their future. If I send them a signal, they will receive it instantly in their frame of reference, but this instant is for ME at t=2x/c.
This geometry is very simple to understand, and if it is not understood, it only comes from a kind of intellectual reluctance to change our own notion of present time.
R.H.