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http://www.eso.org/public/teles-instr/t ... ctroscopy/

Hello Jean-Paul,

I think this is a too simplistic view of emission/absorption phenomena.

In my opinion, the example is not well chosen. It seems to show that all stars have a continuous spectrum without absoption/emission lines (that's false) and it seems to explain that all the emission/absorption phenomena is due to nebulae between stars and observers (this is false too). Instead, most of the emission and absorption lines on spectrum are the results of stars atmospheres, winds and accretion disks which is the really neighborhood of stars.

I prefer this kind of picture, less cartoony (as Steve Shore said) :





Regards,
Vincent

Hello,


keep in mind that a star can emit light which excite a gaz (ex: planetary nebulae, diffuse nebulae) which will reemit light when the gaz desexcite. But a gaz could stay excited for very very long time, long time after the source of excitation and desexcite during long period of time, as "fossile" emission.

A good exemple is hydrogen and 21cm line seen in radio - this is a fossile emission, of course of very low energy.


Cordialement,
Olivier Thizy
http://observatoire-belle-etoile.blogspot.fr/

In addition to this old post, do not forget that emission is from excited gaz. Excitation can be radiative (light from a source excite the gaz) but also from physical shock from other particles such as a Wind. So we could see emission line wihout having a light source...