The black lines that show red shift are confusing me, would anyone be able to explain to me how they're collected and what they can show. i get that an increase in wavelength of light means its red shift and if there are 2 to compare then the one towards the red side shows red shift, but I don't understand what is meant by the dark lines that can be found in the spectrum and what they are?
Red shift is where light waves coming from distant galaxies are shifted to the red end of the spectrum, so if you compared the absorption spectra (black lines) of a near galaxy and far galaxy the far galaxy's black lines would be far more shifted to the red end and closer galaxies will have the black line closer to the absorption spectra of our galaxy.
This is because further away galaxies are moving at higher speeds than ones closer to us. Further to the red side of the spectrum the faster it is moving away from us. So by this you are able to tell that the universe is always expanding.
I hope this helped!