How does redshift reveal that distant galaxies are moving away?

Redshift reveals that distant galaxies are moving away from us through the Doppler effect, a phenomenon where the observed wavelength of light changes based on the relative motion between a source and an observer.12

As a galaxy recedes from Earth, the distance between successive light wave crests increases, stretching the light toward longer, redder wavelengths. This shift is measured by comparing the observed wavelength of a galaxy's spectral lines to their known "rest" wavelengths.23

In the context of cosmology, this is known as cosmological redshift. American astronomer Edwin Hubble discovered that the redshift of a galaxy increases proportionally with its distance from Earth, a relationship now known as Hubble’s law. This observation provides fundamental evidence that the universe is expanding, with galaxies moving away from one another as space itself stretches. The faster a galaxy is receding, the greater the redshift observed in its light.245