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Re: sun's spectrum



Certainly light comming from the sun to my eyeball must be pretty well
collimated.

On Fri, 30 Jan 1998 10:35:28 -0800 Leigh Palmer said:
On Fri, 30 Jan 1998 07:07:30 -0600 brian whatcott said:
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.

My understanding was that when the hydrogen etc. absorb photons that were
directed toward me, they reradiate photons in all directions and therefore
I see fewer photons than I would have if the gasses had not been there.
Hence dark lines. However, this does not seem to help understanding of
the experiment Bob Sciamanda describes. Any insights?

That would be a correct explanation if the incident radiation is
collimated, like the absorption of radiation from a more distant
star by a nebula. 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