Re: sun's spectrum

[Leigh Palmer <palmer@sfu.ca>]

> 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