All celestial bodies (as well as the Earth) are traveling through the space-time of the Universe along with the distortions (contraction) of the contiguous, warped by the bodies themselves (and belonging to them) time-spatial domains, which we can name “near the surface of the celestial bodies”. The intensity of the gravitational field “near the surface of the celestial body”, remains practically the same, during the travel of the celestial body through the space, because the intensity of the gravitational field is determined (dominated) by the mass of the celestial body. The speed of light in vacuum (in the stationary empty space), in any particular local time-spatial domain, corresponds to the intensity of the gravitational field in this time-spatial domain. Therefore, during the travel of the celestial body through the space, the constant intensity of the gravitational field “near the surface of the celestial body” determines the constant “speed of light in vacuum” there.
Therefore, that is the reason why there is no variation in “the speed of light in vacuum” when the Earth moves in its orbit around the Sun and together with the Solar System in the Galaxy.
That is the reason, why the experiments carried out “near the surface of the Earth” cannot detect any change in the “speed of light in vacuum”, due to the travel of the Earth “through the ether”, which turns out to be the space itself.
One can say that the speed of light in vacuum is the same for the whole Universe – that it is a fundamental constant. However, it is a big delusion, because actually the speed of light in “empty space” is different in regions with different intensity of the gravitational field. As was mentioned above, the “Shapiro time delay effect” is proof of this reality.
Furthermore, using a laser technique, various experiments can be made on board an orbital station, (where the gravity is weaker) – to prove the change (the increase) of the wavelength and frequency of given electromagnetic radiation… and this is actually the proof that aboard the orbital station, the speed of light in a vacuum is higher!
On the basis of the “Model of the Physical Reality in the Universe”, a“Thesis about the Behavior of the Electromagnetic Radiation in Gravitational Field” is proposed in chapter 10 of the book, which actually rejects the accepted by the contemporary physics “postulate of the constancy of the speed of light for all inertial frames of reference for the entire Universe”.