This is probably a stupid question - but I guess I am doomed to remain stupid if I don't ask, but there is a chance for me to become a little bit less stupid if somebody can provide an answer ...
Given that our atmosphere is composed of a lot of nitrogen (78%), oxygen (21%), and a smattering of other "stuff", how is it that we are able to do ANY spectroscopic or narrow-band observation in the wavelengths corresponding to the major constituents of our atmosphere?
"Telluric contamination" is an issue at some wavelengths, but why isn't the absorption from the major atmospheric components so overwhelming as to render observation of OIII emission nebulae impractical, for example?
