On Wed, 26 Sep 2007 05:32:46 -0700, George Dishman
wrote:

On 26 Sep, 11:49, HW@....(Dr. Henri Wilson) wrote:
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...

Why would you imagine they would? The opacity
of the gas just above the photosphere is higher
at the specific frequency we call hydrogen Alpha
than at other frequencies between such resonances.
You even claimed you had taken pictures in H alpha.

Sorry I misread your statement...
It's OK..

...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?

So the amount of energy that falls outside a
bandpass filter from 2000 to 2400 nm because
of the shift is negligible hence the temperature
measurement based on that value is valid.

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.

The shift is measured from specific lines,
you cannot measure a shift of 0.01% in the
continuum which is never exactly a black
body because of the finite thickness. This
is all obvious stuff Henry.

George, let's get this straight.

You say temperature is estimated by comparing the energy arriving in the two
fliter bands and assuming a black body curve.

I say the average light in the two bands can come from slightly different
layers with different radial velocities. ADoppler can shift the light by much
more than 0.01% and might easily lead to false ratios in the two bands.

George

Henri Wilson. ASTC,BSc,DSc(T)

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