In studying the chapters on cosmology in Misner/Thorne/Wheeler (what a textbook!), I see that the cosmological redshift is different than Doppler. If I understand correctly, it is due to the expansion of the (Friedman, FLRW) universe during the photon’s long journey to us, rather than being due to some enormous retreating velocity during its emission. So my question is how do we distinguish between the two effects in astronomy? Or can we? Or do we need to tell the difference? If we have recently determined that the “expansion of the universe” is accelerating, is that one type or the other, or the sum of the two, etc.? And where do the energy and momentum of a red-shifted photon go as it is reduced, either during emission or its journey to us? Thanks.