Cosmological Redshift

Stretching of light wavelengths by the expansion of space, the primary evidence for the expanding universe.

Vesto Slipher measured the first galaxy redshifts in 1912; Hubble's 1929 distance-velocity relation tied them to cosmic expansion.
It arises because expanding space stretches light waves in transit, not from motion through space as in the Doppler effect.
The James Webb Space Telescope has confirmed galaxies at redshifts above 14, seen less than 300 million years after the Big Bang.