Should the constancy of the speed of light in vacuum be understood to have the value c "relative to the material detector" and not necessarily c relative to the reference frame of description?

An experiment observing a distant celestial body could be performed to check that alternative interpretation to the Special Theory of Relativity.
- First: Observe (and photograph) the distant body with a powerful telescope when the body is near the horizon of the observation site. I must be a body that can be seen either looking east or west (but not looking north or south).
Doing so, the body will be observed when the Earth has its maximum (or its minimum) annual speed relative to the body.
- Second: Photograph again the body 6 months later and again when the body is near the horizon of the observation site.
If in the first observation the detector (the Earth) was "approaching" the body it will now be "receding" from it (and vice versa).

Let v be the orbital speed of the Earth around the sun (v =30 Km/sec approximately).
Let d be the average distance between the body and the Earth.
If it happened to be true that the speed of light in vacuum is c relative to the primary detector (in this case the Earth's atmosphere) and not necessarily c relative to the description frame (the sun) nor to the emitter (the body) then
- The light received in the first observation will have travelled the distance d with a speed c-v (or alternately c+v) relative to the sun while in the second observation the observed light will have travelled the distance d with a speed c+v (or alternately c-v) relative to the sun. That difference of speeds imply that the first observation is receiving the light emitted from the body at an epoch t1 earlier than the epoch t2 in which it emitted the light received in the second observation. If the body is very far away the difference t2-t1 will be much bigger than the 6 months delay between the two observations (that should also be accounted for).

If the observed body was changing significantly any of its features (luminosity, size, spectroscopy,...) during the time interval (t1, t2) then the photographs will reveal changes unable to have taken place in only 6 months.
Perhaps the remnants of a supernova are a good candidate body for the experiment but the astrophysicists might know of a better candidate.

Please see more details at the YouTube video

https://www.youtube.com/watch?v=cMwFjqGeAtE

The analysis of the experiment begins at
https://youtu.be/cMwFjqGeAtE?t=1584