Re: sun's spectrum

[Leigh Palmer <palmer@sfu.ca>]

> > . . .                              Emission lines are those for which
> > the radiant flux is greater than the flux at adjacent wavelengths.
> > they show as peaks in a spectrum of intensity plotted against
> > wavelength. The Sun has none to speak of in the visible, and
> > certainly not in the disk for hydrogen, which is abundant in the
> > chromosphere. Emission lines of hydrogen can be seen in solar
> > prominences during a total solar eclipse. In fact they look red.
> > Those with an intense interest in the solar spectrum might like
> > to store this URL:  http://mesola.obspm.fr/form_spectre.html
> >
> > Leigh
> There is a project going on, involving several observatories, which is
> mapping the rotation velocity of the sun's surface by carefully measuring
> (and mapping) Doppler shifts in the H alpha line as a function of position
> on the disk.  Our campus astronomer is involved;  I don't know all the
> details, but I was given to understand that the procedure involved observing
> the disk through an H alpha filter.  Does this jive with what you're saying,
> Leigh?  Perhaps it is just that the H line is there but it does not stand
> out in brightness against the continuum. (?)

I have no special knowledge regarding the observation of structure in
H-alpha light. "The" spectrum of the Sun I take to mean the integrated
light from the whole disk. I don't think that a spectrum taken from any
part of the disk shows emission lines either, but I could easily be
incorrect. One can still have strong contrast features when observing
within an absorption line. For example, suppose one has an 80%
absorption in one part of a feature and 95% absorption in another part.
(By this I mean, of course, that one would interpret them that way by
measuring intensity - one has a flux density which is 80% of the disk
average outside the absorption line and the other 95%. I don't mean
that the actual absorption of the chromosphere varies in that manner.)
The contrast between the two areas is a factor of four in brightness.

Perhaps you could help us by asking your colleague for help. Ask him if
the H-alpha light he's observing in is within the Fraunhofer absorption
linewidth. I'm betting it is.

Leigh