Displacement of the
spectrum of an astronomical object toward longer wavelengths (visible light shifts toward the red end of the spectrum). In 1929
Edwin Hubble reported that distant galaxies had redshifts proportionate to their distances (
see Hubble's constant). Since redshifts can be caused by motion of an object away from the observer (the
Doppler effect), Hubble concluded that all galaxies are receding from each other. This became the cornerstone of theories of an
expanding universe.
For more information on redshift, visit Britannica.com.