zine-ye damâ (#)
Fr.: gradient de température
A physical quantity that describes the rate of change of temperature with displacement in a given direction from a given reference point. Same as → thermal gradient.
Fr.: inversion de température
Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.
Fr.: perturbation tensorielle
The perturbation in the → primordial Universe plasma caused by → gravitational waves. These waves stretch and squeeze space in orthogonal directions and bring about → quadrupole anisotropy in incoming radiation temperature.
Fr.: température thermodynamique
A temperature scale, measured in → kelvin (K), that is related to the energy possessed by matter; it was formerly known as → absolute temperature. The zero point on the scale (0 K) is absolute zero. Thermodynamic temperature can be converted to temperature on the → Celsius scale by subtracting 273.15.
Fr.: supernova thermonucléaire
Same as → type Ia supernova
andiš-âzmâyeš, âzmâyeš-e andišeyi
Fr.: expérience de pensée
A demonstration which is carried out in the realm of the imagination, rather than in a laboratory. Thought experiments are designed to test ideas, theories, and hypotheses which cannot physically be tested, at least with current scientific equipment. Some examples: → Maxwell's demon; → Einstein's elevator; Heisenberg's gamma-ray microscope; → Schrodinger's cat. Also called Gedanken experiment.
time of periapsis passage
zamân-e gozar az pirâhabâk
Fr.: temps de passage au périapse
âzmâyeš-e carx-e dandâne-dâr
Fr.: expérience de la roue dentée
The experiment which provided the first accurate measurement of the speed of light. The experiment, conducted by the French physicist Armand H. L. Fizeau (1819-1896) in 1849, used a rotating wheel containing 720 teeth. The function of the wheel was to cut a light beam into short pulses and to measure the time required for these pulses to travel to a distant mirror and back (17.34 km). The round-trip time for each pulse could be calculated to be about 1/18,000 sec, which yielded the value of 315,300 km/sec for the speed of light. Leon Foucault (1819-1868) improved on Fizeau's method by replacing the cogwheel with a rotating mirror. Foucault's estimate, published in 1862, was 298,000 km/s.
Âzmâyeš, → experiment; carx→ wheel; dandâne-dâr "toothed," from dandân "tooth," Mid.Pers. dandân; Av. dantan-; cf. Skt. dánta-; Gk. odontos; L. dens (Fr. dent); Lith. dantis, O.Ir. det, Welsh dent; PIE base *dont-/*dent- "tooth."
Fr.: expérience de Trouton-Noble
An experiment first carried out in 1903 to reveal the absolute motion of the Earth with respect to the → ether. The experiment consists of detecting a torque on a charged parallel-plate → capacitor that was suspended so that its plates were vertical. Since the Earth moves around the Sun, the moving charges were expected to produce magnetic fields, and the resulting torque should tend to turn the capacitor bringing its plates parallel to its velocity. No such effect was observed, and the absence of the torque supports the theory of → special relativity.
Named after Frederick T. Trouton (1863-1922) and Henry R. Noble; → experiment.
Type I supernova
abar-now-axtar-e gune-ye I
Fr.: supernova de type I
A type of supernova whose spectra lacks hydrogen lines. Its → light curve exhibits a sharp maximum with a gradual decrease. Typical magnitudes MV = -14 to -17. Ejecta velocities about 10,000 km/sec. Type I supernovae have several subtypes: → Type Ia, → Type Ib, and → Type Ic.
Type Ia supernova
abar-now-axtar-e gune-ye Ia
Fr.: supernova de type Ia
A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain 56Ni → 56Co → 56Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of 56Ni synthesized in the explosion. Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.
Type Ib supernova
abar-now-axtar-e gune-ye Ib
Fr.: supernova de type Ia
A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.
Type Ic supernova
abar-now-axtar-e gune-ye Ic
Fr.: supernova de type Ia
Type II supernova
abar-now-axtar-e gune-ye II
Fr.: supernova de type II
A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from MV = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of → massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.
Type II-L supernova (SN II-L)
abar-now-axtar-e gune-ye II-L
Fr.: supernova de type II-L
Type II-n supernova (SN II-n)
abar-now-axtar-e gune-ye II-n
Fr.: supernova de type II-n
Type II-P supernova (SN II-P)
abar-now-axtar-e gune-ye II-P
Fr.: supernova de type II-P
A → Type II supernova which reaches a plateau in its → light curve. The vast majority of Type II SNe are characterized by a fast (few days) rise to a flat light curve, most pronounced in the reddest optical bands, with a duration of 80-100 days. This plateau phase is interpreted as the recession of the photosphere as the ejecta expand and cool. The spectra of SNe II-P are typically dominated by strong → P Cygni profiles of hydrogen lines, as well as iron absorption features (for a review, e.g., see Filippenko 1997, ARA&A 35, 309).
Fr.: céphéide à très courte période
Fr.: opérateur unitaire
bâlâ (#), zabarin (#)
Higher, as in place, position, pitch, or in a scale.