For other people interested in actual science, there are plenty of resources on cosmological redshift.
How any redshift in astronomy is worked out is quite easy to understand. There are spectral lines in the spectrum from galaxies. There are spectral lines from plasma in labs here on Earth. There are sets of distinctive lines. For example there is a triplet of lines from oxygen. We match up the distinctive lab lines with the distinctive astronomy lines. We see that the only way to get the lines to match is to shift all of the lines toward the red. That is red shift.
How any redshift in astronomy is worked out is quite easy to understand. There are spectral lines in the spectrum from galaxies. There are spectral lines from plasma in labs here on Earth. There are sets of distinctive lines. For example there is a triplet of lines from oxygen. We match up the distinctive lab lines with the distinctive astronomy lines. We see that the only way to get the lines to match is to shift all of the lines toward the red. That is red shift.
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