The Doppler Effect, which is familiar to us in terms of sound waves, also affects electromagnetic waves.
Normally we are talking about light but the same effect would be detected in, for example, microwaves or radio waves.

more redshift

and Yoker Uni’s video about Doppler and stuff

While redshift can be used to tell us about the recession velocity of (non relativistic) galaxies, we also need to find a way to measure the distance to these galaxies.  Astronomers have two main methods to measure these distances; parallax (more parallax here) and cepheid variable stars – there’s a Khan Academy video on cepheid variable stars.

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