a shift in the lines of the spectrum of an astronomical object towards a longer wavelength (the red end of an optical spectrum), relative to the wavelength of these lines in the terrestrial spectrum, usually as a result of the Doppler effect caused by the recession of the object
Compare: blueshift
redshift in American English
(ˈrɛdˌʃɪft)
noun
Astronomy
the shift of spectral lines toward the longer wavelengths and lower frequencies at the red end of the spectrum in a luminous celestial body, indicating that the light source is moving rapidly away from the observer: thought to be a Doppler effect explaining an expanding universe, or the result of a strong gravitational field