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Re: sun's spectrum



At 12:49 1/30/98 EST, David Dockstader wrote:
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?



Bob described a classical experiment where the varying intensity of the
white light (formerly an arc, now an incandescent) appears to throw an
emission line into absorption.
In this case, the flux from the line is constant, and the white light
provides a contrasting ground in high- or low-relief....
This is called 'the reversal of the sodium spectrum'.

The condition for extinction of an emission (or absorption) line is equality
of the temperature of the continuum radiator and that of the thermally excited
line radiator.
(Physics, Starling & Woodall, Longmans)
brian whatcott <inet@intellisys.net>
Altus OK