Fr.: décalage anormal vers le rouge
The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.
Fr.: décalage vers le bleu
The apparent shift of the wavelength towards the shorter wavelength region of the radiation spectrum of an approaching object due to the Doppler effect.
Fr.: composante décalée vers le bleu
A constituent of a composite astronomical object which has a motion directed towards the observer, as revealed by its spectrum.
Fr.: décalage de Compton
Of the → Compton effect, the amount of increase in the wavelength of an energetic photon upon its collision with an electron.
sorxkib-e keyhânšenâsik, ~ keyhânšenâxti
Fr.: décalage vers le rouge cosmologique, redshift ~
The → redshift of a remote object (galaxy, quasar, supenova) due to the expansion of the Universe.
→ cosmological; → redshift.
Fr.: décalage Doppler
Effect of the relative motion of a wave source (light, sound) and the observer. If the source is moving away, the wavelength is stretched (shifted toward lower frequencies). If the source is approaching, the wavelength is compressed (shifted toward higher frequencies). These effects, known as Doppler shifts, are in the case of light waves called redshift and blueshift, respectively.
→ Doppler effect; → shift.
Fr.: décalage de fréquence
The change in the frequency of a wave motion due to the → Doppler effect.
Fr.: décalage vers le rouge gravitationnel
The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity.
→ gravitational; → redshift.
high redshift object
Fr.: objet à grand décalage vers le rouge
A galaxy or quasar having a → redshift larger than about 0.8, corresponding to a → look-back time half the present age of the Universe. The qualifier "high" is, however, relative and depends on context and authors' assessment.
Fr.: décalage isotopique
A displacement in the spectral lines due to the different isotopes of an element.
Fr.: décalage de Lamb
A tiny change in the → energy levels of the → hydrogen atom between the states 2S1/2 and 2P1/2, which creates a shift in the corresponding → spectral lines. The 2P1/2 state is slightly lower than the 2S1/2 state, contrarily to the Schrodinger's solution. The difference is explained by the interaction between → vacuum energy fluctuations and the hydrogen electron in different orbitals.
Named after Willis Eugene Lamb, Jr. (1913-2008), an American physicist who discovered this effect in 1951, and won the Nobel Prize in physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum;" → shift.
Fr.: faible décalage vers le rouge
A redshift characterizing a near-by receding object.
The portion of the isotope shift which results from the difference between the nuclear masses of different isotopes.
kib-e parâdiš, degarguni-ye ~
Fr.: changement de paradigme
1) Philosophy of science: A process of revolutionary change in scientific
→ paradigms, whereby established scientific ideas are
replaced by new ones. For instance, Copernicus' evidence that the Earth revolved
around the Sun caused a paradigm shift in astronomy.
Fr.: décalage de phase
Any change in the phase of a periodic quantity or in the phase difference between two or more periodic quantities.
Fr.: décalage vers le rouge
A shift in the lines of an object's spectrum toward longer wavelengths. Redshift indicates that an object is moving away from the observer. The larger the redshift, the faster the object is moving. Redshift is expressed by z = Δλ/λ = v/c, where λ is the wavelength, Δλ the wavelength shift, v the velocity of the source relative to the observer, and c the → speed of light. When v approaches c, redshift is expressed by the → relativistic formula z = ((1 +v/c)/(1 - v/c))½ - 1.
Fr.: espace de décalage vers le rouge
The space corresponding to → redshift measurements, as contrasted with real space. See also → redshift space distortion
redshift space distortion
cowlegi-ye fazâ-ye sorx-kib
Fr.: distorsion dûe aux vitesses particulières sur la ligne de visée
The distortion observed in → redshift space of → galaxy clusters caused by peculiar velocities of the members (→ peculiar velocity). In a perfectly homogeneous → Friedmann-Lemaitre Universe the redshifts would accurately measure radial distances from the observer, and the mapping from real space to redshift space would simply be an identity. In an inhomogeneous Universe the peculiar velocities associated with any inhomogeneous structure will introduce a distortion in this mapping (N. Kaiser, 1987, MNRAS 227, 1). See also: → fingers of God, → Kaiser effect.
→ redshift; → space; → distortion;.
bardid-e sorx kib
Fr.: relevé de décalages vers le rouge
A survey of a large region of the sky to measure the redshifts of all the galaxies down to a certain limiting magnitude.
Fr.: relation décalage vers le rouge-distance
The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances.