Do absorption lines have a Doppler shift?
We are studying atomic physics at school which involves the electromagnetic spectrum. We have been shown the absorption spectra for various substances. We have also been shown how if an object like a star is moving towards Earth the Fraunhofer lines will shift slightly to the blue end of the spectrum in a blue shift, and if the star is moving away the Fraunhofer lines will shift slightly to the red end of the spectrum in a red shift. My question is why is it the Fraunhofer lines which shift, as I would have thought the atoms in the atmosphere of both Earth and the star would absorb the same frequency of light regardless of the movement of the star or Earth? I asked my physics teacher and he did not know the answer. Reply Imagine an absorption line in the spectrum of a star. To its right and left in the spectrum are bright emissions, which get shifted by the Doppler effect due to the relative motion between the star and us, in the same direction (to the red or the blue). Would the dark
