Fr.: température absolue
adiabatic temperature gradient
zine-ye damâ-ye bidarrow
Fr.: gradient de température adiabatique
The temperature gradient defining the → radiative equilibrium condition in a region. It is expressed as: dT/dr = (1 - 1/ γ)((T / P)(dP / dr), where T and P are temperature and pressure, dT / dr and dP / dr temperature and pressure gradients respectively, and γ = CP / CV. For radiative equilibrium to be stable against → convection, the actual temperature gradient must be less than the adiabatic temperature gradient, i.e. |dT /dr|rad < |dT /dr|ad. See also → Schwarzschild's criterion.
Fr.: température d'antenne
In radio astronomy, a measure of the power absorbed by the antenna. In an ideal, loss-free radio telescope, the antenna temperature is equal to the brightness temperature if the intensity of the received radiation is constant within the main lobe. → antenna; → temperature.
antenna; → temperature.
damâ-ye siyah-jesm (#)
Fr.: température de corps noir
The temperature at which a blackbody would emit the same radiation per unit area as that emitted by a given body at a given temperature.
Fr.: température de brillance
In radio astronomy, the temperature of a source calculated on the assumption that it is a blackbody emitting radiation of the observed intensity at a given wavelength. → antenna temperature.
Fr.: température de couleur
The temperature of that black-body which has the same spectral energy distribution in a limited spectral region, as the object under study has.
damâ-ye Curie (#)
Fr.: température de Curie
The highest temperature for a given → ferromagnetic substance above which the → magnetization is lost and the substance becomes merely → paramagnetic. The Curie temperature of iron is about 1043 K and that of nickel 631 K.
Named after the French physicist Pierre Curie (1859-1906), a pioneer in magnetism, crystallography, and radioactivity. In 1903 he received the Nobel Prize in Physics with his wife Marie Curie (1867-1934, née Maria Skłodowska), and Henri Becquerel (1852-1908); → temperature.
damâ-ye Debye (#)
Fr.: température de Debye
Fr.: température de poussière
An indication of the heat amount received by → dust grains from the ambient → radiation field. Dust temperature depends on the optical properties and → sizes of grains (i.e., on the way they → absorb and → emit radiation) as well as on the → interstellar radiation field. Most of the visible and → ultraviolet radiation in galaxies from stars passes through clouds of particles and heats them. This heating leads to re-radiation at much longer wavelengths extending to the millimeter.
Fr.: température effective
A measure of the surface temperature of a star derived from the total emitted energy, assuming that the star is a → blackbody emitter (→ Stefan-Boltzmann law, → Planck's radiation law). See also → brightness temperature; → color temperature.
damâ-ye Einstein (#)
Fr.: température d'Einstein
damâ-ye elektroni (#)
Fr.: température électronique
1) The temperature of electrons in an interstellar ionized nebula (e.g. in
→ H II regions and
→ planetary nebulae) as determined by characteristic
→ emission lines (optical
→ forbidden lines or
→ radio recombination lines).
Fr.: température d'excitation
Of a gas or plasma, the temperature deduced from the → populations of atomic → excited states, as expressed by the Boltzmann formula: Nu/Nl = (gu/gl) exp (-ΔE/kTex), where Nu and Nl are the upper level and lower level populations respectively, gu and gl the statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h→ Planck's constant. The higher the energy of the occupied states, the higher the excitation temperature.
Fr.: température de Hawking
The temperature inferred for a → black hole based on the → Hawking radiation. For a → Schwarzschild black hole, one has TH = ħc3/(8πGMk) where ħ is the → reduced Planck's constant, c is the → speed of light, G is the → gravitational constant, M is the mass, and k is → Boltzmann's constant. The formula can approximately be written as: TH≅ 6.2 x 10-8 (Msun/M) K. Thus radiation from a solar mass black hole would be exceedingly cold, about 5 x 107 times colder than the → cosmic microwave background. Larger black holes would be colder still. Moreover, smaller black holes would have higher temperatures. A → mini black hole of mass about 1015 g would have TH≅ 1011 K.
Fr.: température de Hayashi
The minimum → effective temperature required for a → pre-main sequence star of given mass and radius to be in → hydrostatic equilibrium. This temperature delimits the boundary of the → Hayashi forbidden zone.
Fr.: température d'inflammation
The minimum temperature to which a fuel must be heated in order to initiate self sustained combustion independent of another heat source.
damâ-ye jonbeši (#)
Fr.: température cinétique
The temperature of a gas defined in terms of the average kinetic energy of its atoms or molecules.
Fr.: température de bruit
A means for specifying the noise generated as unwanted → electromagnetic radiation in a receiver system or one of its components. It is usually measured in terms of the equivalent temperature in a → Rayleigh-Jeans spectrum. Noise temperature is used mainly in radio astronomy.
Fr.: température protonique
The temperature in the → solar wind, as derived from the mean kinetic energy of protons: mv2/2 = (3/2)kTp, where k is → Boltzmann's constant. There are two types of proton temperature: parallel temperature, measured from protons moving parallel to the magnetic field, and perpendicular temperature relating to protons at right angles to the magnetic field. The proton temperature is usually derived using particle detectors on board space probes that determine the velocity → distribution function of the particles from their energies (N. Meyer-Vernet, 2007, Basics of the Solar Wind, Cambridge Univ. Press). See also → electron temperature.
Fr.: température de rayonnement
The temperature of a source calculated assuming that it behaves as a → blackbody that radiates with the same intensity at the same frequency. Compared to the → effective temperature, the radiation temperature is measured over a narrow region of the → electromagnetic spectrum.