Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:
Speed of waves in a dispersive medium is temperature dependent.
Maybe.. depends on the medium, I should think, and the mechanism of the
dispersion. Some dispersion might be due to ionization (which may or may
not be temperature dependent).

It is known that the speed of light in air is temperature dependent ( mirage
and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.
In the Solar System the temperatures are decreasing with the distance
from the Sun.

Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles. When
the number density gets down in the "few atoms per cubic meter" and the
mean free path gets to be meters or km, I think you need to start thinking
in different ways.

May be, but at first I must know if the mirage works in vacuum.
One common confusion is an assumption of a particular velocity
distribution in charged particles and then using the 11000K = 1 eV
relation.

Yes. But the simple measurement of the mirage or E. Schmidt's effect in
vacuum will clarify everything.
"I am sure that such experiments were done". Could you help?
S*



How about Ordinary and Extraordinary rays in the dispersive medium of
the ionosphere. Is the ionosphere "vacuum" enough for you? The space
station orbits in the middle of it, and most folks think that qualifies
as vacuum (1e-6 Torr, or so). Electron density runs pretty high: about
1E10-1E12/m3

At the top, the pressure runs about 1E-5 Pascal (7.5E-8 torr) & mean
free path is on the order of tens of km.


There's lots and lots and lots of data about dispersion of EM
propagation in the ionosphere.

Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)