redshift

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redshift

(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.

redshift

[′red‚shift]
(astrophysics)
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 ?
In the second step of tonotopic shift simulation, a noise-band synthesis was performed using the various enhanced speech stimuli processed through eight channels with three degrees of spectral shift.
In the processing condition where no spectral shift is present, the synthesis filters are exactly identical to the analysis filters.
Spectral shift was performed in 3 different ways by shifting the synthesis filters from the analysis filters by a frequency separation that corresponded to a shift of 0, 3 and 4.
Corresponding to the 4 sets of stimuli and 3 spectral shift values (0, 3 and 4.
Following the completion of pilot test, the subjects were tested with the sentences processed through the various spectral shift conditions.
The Table I shows the percent correct scores using the three noise reduction methods as well as the noisy condition for various values of spectral shift.
The spectral shift value of 0 mm, corresponds to the condition of no frequency mismatch and hence produced highest speech recognition across all the 4 different processing methods compared to the other two conditions of spectral up shifting.
3 Gravitational spectral shift exterior to oblate spheroidal distributions of mass
By shifting the model spectrum to the red where the emission spectrum of the currently used calibration standard, bead3, stands, the possible error due to the spectral shift combined with variation in transmission of the dichroic filter in the observation window was modeled (Fig.
A modified Lippert equation (13) was used in a separate study to correlate the spectral shifts in terms of the dielectric properties of the solvent and polymer bead materials (the result is not published yet).
Orbital motion, by contrast, displays the simple clocklike stability actually seen in the stars' spectral shifts.
Self-quenching in conjunction with spectral shifts may become important if the density of immobilized fluorophores is large.

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