- a shift toward longer wavelengths of the spectral lines emitted by a celestial object that is caused by the object moving away from the earth.
- 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 objectCompare: blueshift
- See under Doppler effect.
In physics, the reddening of light sent out by an object that is moving away from an observer. (See Doppler effect.)