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Re: sun's spectrum - riposte



At 07:29 1/30/98 -0800, Brian wrote:
As Kirchhoff pointed out in connection with thermal radiation, good
absorbers are in general good emitters. (In fact Prevost [1792] said
as much.)
So these 'absorption' lines do not in fact represent a loss of flux -
rather a contrast effect with the continuum radiation surrounding.

I'm not sure what point Brian is making here. The chromosphere acts
as a filter, absorbing light from the photosphere so that it does
not get through to us. It does result in a reduction of flux at those
wavelengths. There is still some flux left at those wavelengths, from
the chromosphere itself, but it is much attenuated with respect to
that at nearby wavelengths. In fact this morning I will introduce my
students to the Saha equation so they can understand those lines in
some detail.

Leigh

In the case of the chromosphere the radiation
is incident over a hemisphere, crudely speaking, and almost as
much is scattered into the line of sight as is scattered out.
Thus it is the effectof difference in temperature that dominates.

Is that good for insight?

Leigh

In that Leigh is locating the absorption mechanism in the
chromosphere his insight appears to falter.

With the arrival of Roger Freedman's rather handsome solar post
this morning, I believe Leigh is now better placed to examine
objections to his explanation.

It is not the hot chromosphere doing the absorbing, but rather
the outer, cooler layer of the photosphere.

Sincerely
Brian

brian whatcott <inet@intellisys.net>
Altus OK