Hi, Fubaruk!

There is a frequent poster here who I hope will see your post and provide
you with a set of links to other threads which have discussed your main
question at length.

Light traveling through any medium slows down, but what is happening
on an atomic and photon scale is quite likely that the photons travel from
one electrically-charged particle to the next at the speed of light, then
are momentarily absorbed by the particle and emitted again a short time
later. The delays are the result of the time the energy is tied up in the
charged particles. Some very strange materials have been developed in
recent years which allow photons to keep on traveling from one particle
to the next for a very long time without getting permanently absorbed
or scattered in all directions.

Others can give you more complete descriptions.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves