[Bored chemist]

Pressure broadening, because the gas has an increasing density as you get closer to the surface

Funny stars in your universe.

ANyway, I think Alan's point is that, if there were some"etner" then, if it varied at all with time or space then it would make stars "twinkle" in much the same was at the atmosphere. Occasionally, it would een send light off at right angles to where it was expected.

The fact that we don't see even that slightest bit of twinkling suggests that, if there  is an "ether" it is incredibly homogeneous- which is fine as an hypothesis, but at odds with the idea of "ether drag"- which is needed to get round things like the MM experiment