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(red -shift) A displacement of spectral lines toward longer wavelength values; for an optical line, the shift would be toward the red end of the visible spectrum. The redshift parameter, z, is given by the ratio δλ/λ, where δλ is the observed increase in wavelength of the radiation and λ is the wavelength of the spectral line at the time of emission from a source, i.e. the wavelength in the ‘normal’ terrestrial spectrum.

The redshifts of astronomical objects within the Galaxy are interpreted as Doppler shifts (see Doppler effect) caused by movement of the source away from the observer. The value of z is then v /c , where v is the relative radial velocity and c is the speed of light. The redshifts of extragalactic sources, including quasars, are also interpreted in terms of the Doppler effect, which for these objects results from the expansion of the Universe. The redshift parameter of a distant galaxy thus gives its velocity of recession; since recessional velocities can be very great, the relativistic expression for redshift must be used:

z = [(c + v )/(c v )]½ – 1

From measurements of galactic redshifts it has been possible to calculate the distances of galaxies, using Hubble's law (see distance determination).

The redshifts described above represent a loss of energy by the photons of radiation in overcoming the effects of recession or expansion. There is another mechanism, however, by which redshifts can be produced, i.e. by which photons can lose energy – the presence of a strong gravitational field. This gravitational redshift was predicted by Einstein in his general theory of relativity. Although the redshifts of galaxies are often interpreted as being caused by the relativistic Doppler effect alone, both the expansion and the gravitational field of the Universe are involved. See also cosmological redshift.


A systematic displacement toward longer wavelengths of lines in the spectra of distant galaxies and also of the continuous portion of the spectrum; increases with distance from the observer. Also known as Hubble effect.
References in periodicals archive ?
The highest redshifted objects, registered by the astronomers, are now the galaxies UDFj-39546284 (z = 10.
For the most distant galaxies, cosmic expansion has redshifted their ultraviolet output into the near-infrared.
Each observer anywhere in this Universe will determine that the incoming photons are redshifted.
The photon emitted in an orbital transition of an electron in an atom can only be redshifted if its mass is initially small.
The absorption lines created by hydrogen found in intervening clouds and galaxies are also redshifted.
The faintness of the galaxy in the infrared, its brightness at radio wavelengths, and the detection in visible light of what appears to be the redshifted glow of hydrogen gas all indicate that the team sees the galaxy as it appeared when the universe was just 8 percent of its current age, Rawlings says.
The first step in locating it was to identify faint candidate objects behind the gravitational lens that had the right infrared colors for a very highly redshifted object.
Dim bursts also appear redshifted, says study collaborator Robert J.
But this is not the case when one is viewing distant galaxies whose light has been highly redshifted by the universe's expansion.
These X-rays appear redshifted -- shifted to longer wavelengths - because of the gravitational tug exerted on the photons by the massive black hole.
Originally, its temperature was 3,700 [degrees] K, but it has been redshifted that far by the expansion of the universe.