From Newton’s time to the middle of the 20th century it was generally believed by scientists that the atmosphere of the Earth extended to a certain altitude, around 80 km, whereafter the perfect vacuum of space began.
In the 1950’s “most scientists visualised our planet as a solitary sphere traveling in a cold dark vacuum of space around the Sun”
In 1919 The Royal Society of London sent out two expeditions to observe a total eclipse of the sun, the purpose of which was to view a star beyond the sun whose position would be seen as being close to its surface when shielded by an eclipse of the moon.
One went to Sobral in Brazil and one to the island of Principe, off West Africa, and the latter was led by Sir Arthur Eddington.
Photographic plates were exposed at the time of the eclipse in both places and later analysis showed that the position of a star that was near to the suns surface was shown to deviate from its true position by about 1.6” (seconds of arc) in Principe and 2” in Sobral.
Eddington considered the possibility of gases surrounding the sun having a refractive effect and accordingly worked out what would be the necessary density to produce the required refractive index, but concluded: – “It seems obvious that there can be no material of this order of density at such a distance (an altitude of 400,000 miles) from the sun”.
In other words he made an assumption, based upon the beliefs current at this time, that there was a perfect vacuum at this altitude above the sun’s surface, and accordingly assumed that this result was a proof of Einstein’s prediction of a relativistic influence.
Today however the picture is different. The sending of satellites into orbit around the Earth and probes further out into the solar system and the moon landings have demolished the belief in a thin and finite layer of terrestrial atmosphere, and at altitudes of 300-400 km it is known that the proportions of oxygen and nitrogen are in the same ratios as at sea level. And it is also now known that the atmosphere of the earth has no defined border at any altitude.
‘The sun too has an atmosphere, and because the sun accounts for more than nine tenths of the total mass of the solar system, its atmosphere is much larger than that of any planet. The solar atmosphere extends far beyond the orbit of the earth, and at 80,000 Km our atmosphere merges imperceptibly with that of the sun.’
Of course the density of the solar atmosphere at any point in the solar system is dependent upon the particular altitude from the sun, and the density of its extended atmosphere is influenced by the Earth and other planets and other lesser satellites.
With respect to the Earth, it is now acknowledged that:-
“Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude. This refraction is due to the velocity of light through air decreasing (the index of refraction increases) with increased density.”
As it is known that the Sun has an atmosphere that extends beyond the Earth’s orbit and accordingly merges with the Earth’s volume of atmospheric influence, then it is obvious that there is no clearly defined border between the two.
Accordingly there can be no, arbitrarily defined, altitude from either body where the refraction of light begins or ends and thus where its velocity is constant.
It is now known that space is not a perfect vacuum, the Sun also has an atmosphere that extends far beyond the Earth’s own sphere of atmospheric influence, and that in inter-galactic regions there is a consistent distribution of matter, but of course at densities that are at or near the lowest occurring universally.
In these circumstances it is quite obvious that light will always travel at a speed appropriate to the density of the medium and that light never travels at a constant speed (apart from short distances through a solid, translucent matter such as glass).
Thus light when emitted from one of the Jovian moons, as it emerges from behind that planet, will accelerate up to the point of gravitational neutrality, and density, between it and the planet, it will then decelerate up to where it passes the tangential point of greatest density of the Jupiter’s atmosphere, whereupon it will again progressively accelerate to the point of neutrality between Jupiter and Earth (this assuming no other planetary influences are involved during this passage) and again, as discussed, it velocity will progressively decrease down to the Earth’s surface.
It is therefore clear that an increasing density of the medium results in an increasing inhibitory effect on the motion of light, but in terms of the currently accepted atomic structure of gaseous, macroscopic matter, which assumes that it is composed mostly of ’empty space’, a vacuum, this is inexplicable, as this theory assumes that light is somehow transported through a vacuum that, by definition, can have no inhibitory effect.*
If c is calculated on the basis of the average velocity of light through the variable densities of matter between the Earth and Jupiter, then in the progressively decreasing densities outwards to the median points between the Sun and the nearest stars and onwards to these points between the “Milky Way” and the nearest galaxies, its velocity at any point will be appropriate to the variable densities of matter in these positions.
And as the densities of gases here in these regions are significantly lower, its velocities will accordingly, and also significantly, exceed the hypothetical maximum “c”.
* Mark D. Roberts – Vacuum Energy P 15 :- “If one considers the propagation of light, the speed c is its speed of propagation in a vacuum, there is never an absolute vacuum so that light never propagates at c.” https://arxiv.org/pdf/hep-th/0012062.pdf