Instruction:
What do redshifts tell astronomers?

Response:
Edwin Hubble discovered in the 1920s that the spectral lines of light reaching us from the universe's most distant galaxies were redshifting to areas of the electromagnetic spectrum with lower energy intensity. This allows us to confirm that the various objects in the universe are moving away from us and from one another. The faster a galaxy moves away from the observer, the further it is from the observer. This phenomenon is interpreted as proof of the universe's expansion and the Big Bang.