padidâri-ye fariz (#)
Fr.: visibilité des franges
Optics: If the intensity in an interference fringe pattern has the maximum and minimum values Imax and Imin, the visibility is defined by the relation ν = (Imax - Imin) / (Imax + Imin), where 0 ≤ ν ≤ 1. In terms of the intensities of the two interfering waves: ν = 2(I1 . I2)1/2 / (I1 + I2).
Fr.: anneau G
Fr.: diffusion géométrique
A type of scattering in which the wavelength (of the light or the sound) is much smaller than the size of object causing the scattering.
Fr.: anneau ténu
An extremely faint and broad ring (in fact two rings) of tiny particles around → Jupiter lying just outside the main ring.
Gossamer "a film of cobwebs floating in air in calm clear weather; an extremely delicate variety of gauze, used esp. for veils," from M.E. gossomer, from gos "goose" + somer "summer." Possibly first used as name for late, mild autumn, a time when goose was a favorite dish, then transferred to the cobwebs frequent at that time of year; → ring.
Halqé, → ring; tanté "cobweb, spider's web," from tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" PIE base *ten- "to stretch"), Pers. târ "string," tur "fishing net, net, snare," and tâl "thread" (Borujerdi dialect) belong to this family; variants tanta "cobweb," tanadu, tafen, kartané, kârtané, kâtené, Pashtu tanistah "cobweb;" cf. Skt. tantu- "cobweb, thread, string."
Fr.: érosion des grains par pulvérisation
The ejection of atoms from interstellar dust grains due to impact by gas ions, which leads to grain destruction.
→ grain; sputtering, from sputter "to spit with explosive sounds," cognate with Du. sputteren.
Osparâni, verbal noun of osparândan, from os- "out of, outside," → ex- + parândan "to eject," transitive of paridan "to fly" (from Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").
farizhâ-ye Haydinger (#)
Fr.: franges d'Haidinger
The interference fringes seen with thick plates near normal incidence.
W. K. von Haidinger (1798-1871), Austrian mineralogist and geologist; → fringe.
halqe-ye hâlé, ~ hâlevâr
Fr.: anneau de halo
A faint, wide ring around → Jupiter that has the shape of a doughnut. It is about 22,800 km wide and about 20,000 km thick. This ring starts at 100,000 km from the center of Jupiter. The outer edge of the Halo merges into the → Main ring.
xušé bandi-ye pâygâni
Fr.: groupement hiérarchique
A model in which a system of self-gravitating particles will gradually aggregate into larger and larger gravitationally bound groups and clusters.
Fr.: vol stationnaire
The act of one who hovers.
Fr.: correction de l'image brouillée
A technique using a mathematical model of the blurring process to recover the original, sharp image. See also → blurred image.
Fr.: diffusion inélastique
Fr.: franges d'interférence
One of the alternating bright or dark bands produced by optical interference.
Fr.: anneaux de Jupiter
Any of several faint, dark, narrow rings around Jupiter. Jupiter's rings are so faint and tenuous that are only visible when viewed from behind Jupiter and are lit by the Sun, or directly viewed in the infrared where they faintly glow. Unlike → Saturn's rings full of large icy and rock chunks, they are composed of tiny rock fragments and dust. Jupiter's rings are continuously losing material and being resupplied with new dust from → meteorite impacts with Jupiter's four inner moons (→ Metis, → Adrastea, → Amalthea, and → Thebe). Jupiter's rings were discovered by NASA's Voyager 1 in 1979. They are composed of three parts: the → Main ring, a → Halo ring that orbits closer to Jupiter, and a very wide → Gossamer ring that extends far from Jupiter.
Fr.: dernière diffusion
The epoch in the early evolution of the Universe when matter and photons decoupled. Once atoms formed, light and matter stopped constantly interacting with one another, and photons were able to travel freely. As a result, the Universe became transparent. Light from this period is observed today as the → cosmic microwave background radiation. Same as → decoupling era and → recombination era.
last scattering surface
ruye-ye vâpasin parâkaneš
Fr.: surface de dernière diffusion
The set of locations in space corresponding to the → last scattering epoch in the early Universe. It is a spherical surface around the present-day observer from which the → cosmic microwave background radiation appears to emanate.
Fr.: effet Lense-Thirring
An effect predicted by → general relativity whereby a rotating body alters the → space-time around it. This effect can be thought of as a kind of "dragging of inertial frames," as first named by Einstein himself. A massive spinning object pulls nearby objects out of position compared to predictions for a non-rotating object. The effect is important for rapidly rotating → neutron stars and → black holes, but that near Earth is extraordinarily small: 39 milli-arc second per year, about the width of a human hair seen from 400 meters away.
Named after Austrian physicists Joseph Lense (1890-1985) and Hans Thirring (1888-1976), who first discovered this phenomenon in 1918; → effect.
tavân-e gerdâvari-ye nur (#)
Fr.: pouvoir collecteur de lumière
The most important function of an astronomical telescope, which is directly related to the area (or to the square of the diameter) of the main mirror or lens.
Tavân, → power; gerdâvari, verbal noun of gerd âvardan, from gerd "round; around" (Mid.Pers. girt "round, all around," O.Iranian *gart- "to twist, to wreathe," cf. Skt. krt "to twist threads, spin, to wind, to surround," kata- "a twist of straw;" Pali kata- "ring, bracelet;" Gk. kartalos "a kind of basket," kyrtos "curved") + âvardan "to bring," Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring, to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry;" nur, → light.
Fr.: anneau principal
A thin strand of material encircling Jupiter; the main component in → Jupiter's ring system of three parts. The diffuse innermost boundary begins at approximately 123,000 km. The main ring's outer radius is found to be at 128,940 km,
Fr.: diffusion de Mie
The scattering of → electromagnetic waves by → particles of → size comparable to the radiation → wavelength. Mie scattering depends weakly upon the wavelength, hence the → scattered light spectrum is similar to that of the → incident light. Mie scattering explains the → white color of clouds when scattering is due to → water droplets having a size of few microns. Cloud → droplets with a diameter of around 20 microns or so are large enough to scatter all visible wavelengths more or less equally. Because all wavelengths are scattered, clouds appear to be white. When clouds become very deep, less and less of the incoming solar radiation makes it through to the bottom of the cloud, which gives these clouds a darker appearance.
Named after Gustav Adolf Mie (1868-1957), a German physicist, whose theory of 1908 explains the process; → scattering.
Fr.: diffusion multiple
A process of → radiative transfer in which more than one → scattering event may be of importance before → transmission, → reflection, or → absorption. In → radiation-driven winds photon scattering can take place in different → spectral lines. Each scattering occurs in a different spectral line, and successive scatterings occur at lower energies (longer wavelength). The standard theory of line driving (→ CAK model) assumes that photons can be scattered only once in the wind, which is a reasonable assumption for normal → O stars. In → Wolf-Rayet stars, where photons evolve in an atmosphere with a strong → ionization stratification, multiple scattering is important. Indeed the strength of W-R winds appears to exceed the single scattering limit.