On Wed, 26 Sep 2007 01:11:39 -0700, George Dishman
wrote:

On 25 Sep, 22:53, HW@....(Dr. Henri Wilson) wrote:


Of course, the corona for example.

and that layer emits plenty of light.

Oops, no. You forgot Kirchofff's Law again, if it is
really transparent it cannot emit at all.

George, absorption is exponential.
If the layer absorbs only 10% per 100 kms, about 36% will still pass through
1000 kms. The layer will have an emissivity 0 and will still radiate.

See the next paragraph:

In practice
both the outer layer just above the photosphere and
the corona show spectral lines. The upper surface is
cooler than the photosphere so they appear in
absorption while the corona is hotter and the lines
show as emission. What we have been discussing re
temperature is the background continuum excluding the
lines.

There is no continuum emission from the 'transparent'
layer but where there is a resonance and the opacity
is higher at that specific frequency, we see absorption.

That's a funny paragraph.
'opacity' ...'specific frequency' ...I didn't know these had the same physical
dimensions...

...yes..and I have been pointing out that ADoppler can cause a considerable
shift in the planck curve.

And I have been pointing that while it _could_, we
know it _doesn't_, the actual shift is only 0.01%
and such a small shift doesn't affect temperature
determination.

If the shift is only 0.01%, so what?

Note also that if the frequency shift were larger,
it would no longer be a black body curve but in
practice the shift is so small that is negligible.

Many stars do not exhibit black body curves so how would you now if they were
shifted or not.

George

Henri Wilson. ASTC,BSc,DSc(T)

www.users.bigpond.com/hewn/index.htm