An Etymological Dictionary of Astronomy and Astrophysics
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The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.

→ anomalous; → redshift.

The apparent shift of the wavelength towards the shorter wavelength region of the radiation spectrum of an approaching object due to the Doppler effect.

→ blue; → shift.

A constituent of a composite astronomical object which has a motion directed towards the observer, as revealed by its spectrum.

→ blueshift; → component.

Of the → Compton effect, the amount of increase in the wavelength of an energetic photon upon its collision with an electron.

→ Compton; → shift.

The → redshift of a remote object (galaxy, quasar, supenova) due to the expansion of the Universe.

→ cosmological; → redshift.

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.

The change in the frequency of a wave motion due to the → Doppler effect.

→ frequency; → shift.

The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity.

→ gravitational; → redshift.

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.

→ high; → redshift; → object.

A displacement in the spectral lines due to the different isotopes of an element.

→ isotope; → shift.

A tiny change in the → energy levels of the → hydrogen atom between the states 2S_1/2 and 2P_1/2, which creates a shift in the corresponding → spectral lines. The 2P_1/2 state is slightly lower than the 2S_1/2 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.

A redshift characterizing a near-by receding object.

→ low; → redshift.

The portion of the isotope shift which results from the difference between the nuclear masses of different isotopes.

→ mass; → shift.

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.
2) The idea of paradigm shift has been transferred from the sciences to other areas of society and culture, referring to a fundamental reorganization of how people think about an entire topic.

→ paradigm; → shift; → change.

Any change in the phase of a periodic quantity or in the phase difference between two or more periodic quantities.

→ phase; → shift.

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.

→ red; → shift.

The space corresponding to → redshift measurements, as contrasted with real space. See also → redshift space distortion

→ redshift; → space.

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;.

A survey of a large region of the sky to measure the redshifts of all the galaxies down to a certain limiting magnitude.

→ redshift; → survey.

The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances.

→ redshift; → distance; → relation.