"Invisible" <voi### [at] devnull> wrote in message
news:47347b15$1@news.povray.org...
> Gail Shaw wrote:
> > "Invisible" <voi### [at] devnull> wrote in message
> > news:47342cbb$1@news.povray.org...
> >> For light, the velocity varies a little, but it's roughly 300,000 km/s.
> >
> > Ur, no. The speed of light in a vacuum doesn't vary at all. It's a
universal
> > constant.
> >
> > 299 792 458 m.s^-1
>
> Yes, the speed of light *in a vacuum* doesn't vary.
>
> The speed of light in other mediums varies though. ;-)

Kinda. Maybe. Not really. Depends on your definitions. *g*

From wiki
(http://en.wikipedia.org/wiki/Speed_of_light#Interaction_with_transparent_ma
terials)

In passing through materials, the observed speed of light can differ from c.
The ratio of c to the phase velocity of light in the material is called the
refractive index. This apparent contradiction to the universality of the
constant c is a consequence of sloppy (but universally practiced)
nomenclature: what is referred to as light in a medium is really a
light-like hybrid of electromagnetic waves and mechanical oscillations of
charged or magnetic particles such as electrons or ions, whereas light in
the strict sense is a pure electromagnetic wave

---

And it is possible for particles to travel faster than the 'speed of light'
in a particular material. (Though, of course not faster than c)
This is most commonly seen around submerged nuclear reactors and is called
Cherenkov radiation. If you've ever seen a picture of a submerged reactor,
it's that eery blue glow.

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