Correcting Galaxy Luminosities for Absorption ?? As light from distant galaxies traverses deep space towards Earth, some amount of that light is absorbed by various features lying between that emitting galaxy, and Earth receivers. Those features imprint those galaxies' observed Spectra, with Absorption Troughs. (Perhaps there are Emission Peaks as well ??) QUESTION: When calculating galaxies' Luminosities -- to estimate their M-to-L ratio's (say) -- do Astronomers correct for all those "missing photons" from the Absorption Troughs ? To wit, do calculations of galaxies' Luminosities give credit for all of the light actually emitted at the source... or only those photons that actually reach our receivers ?? Is this effect important, or is only a tiny fraction of the photons actually absorbed ??