in astronomy, the systematic increase in the wavelength of all light received from a celestial object; it is observed in the shifting of individual lines in the spectrum of the object toward the red, or longer wavelength, end of the visible spectrum. The effect was discovered by V. M. Slipher of Lowell Observatory. Some red shifts are the result of the Doppler effect, i.e., of the relative motion of the earth and the object away from each other. However, all distant galaxies show a red shift proportional to their distance from the earth as a result of the general expansion of the universe (see Hubble's law); the most distant known galaxies have red shifts that indicate they are moving away from the earth at speeds approaching that of light. Red shifts are also produced by gravitation in accordance with the general theory of relativity. Because of the strong gravitational field, the frequency of the light emitted by atoms in a dense, compact star will be lower and the wavelengths consequently longer; such effects have been observed in white dwarfs. See cosmology.

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