Re: Solar absorption lines
- From: Scott <ss@xxxxxxxxxxxxxxxx>
- Date: Mon, 10 Jul 2006 23:26:21 +1000
Hi Jeff,
Thanks for joining in too.
Electrons also can become unbound from atoms and
radiate freely.
Can you elaborate on what you mean by "radiate freely"?
He means "radiate at any wavelength".
It's still not clear to me what this means. What might the
electron do once it's unbound?
Imagine a thin gas in front of a black background. The
gas is too thin and too cold to have significant blackbody
emission, so all you see is black.
The gas is illuminated by a very strong source of light
off to one side, where you can't see it. This is the same
as looking at the solar chromosphere during an eclipse.
Most of the light of particular wavelengths entering the
gas is absorbed
Yep.
> The
result is a low-intensity blackbody glow from the gas, with
a bright-line spectrum superimposed on it.
Where is the energy coming from to heat the gas to have
a blackbody glow?
If it absorbs a H-alpha photon & then re-emits it, there's no
energy left behind.
The bright-line
spectrum isn't especially bright. Only a small fraction
of the light of a particular wavelength which is absorbed
is then re-emitted at one of the particular wavelengths
toward your eye. The vast majority of it is emitted either
in other directions or at other wavelengths, or both.
Yep.
Now move the source of light behind the gas. You now see
a very strong, high-temperature blackbody radiation, with
the cooler gas again absorbing particular wavelengths of
that light, which causes a dark-line spectrum.
Well that works if the gas doesn't surround the emitter.
(Such as the case of interstellar gas/dust.) Please see my
reply to George in this thread. It has a diagram & an
explanation for why I think this doesn't apply in the
case of the chromosphere.
Scott.
.
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