Fr.: contrepartie optique
An astronomical object with usually weak emission in the → visible found to be the optical representation of the object radiating chiefly in other → wavelengths of the → electromagnetic spectrum.
→ optical; → counterpart.
Fr.: densité optique
The transmittance of a point on a photographic negative equal to the log to the base 10 of the reciprocal of the transmittance through the negative at that point.
Fr.: profondeur optique
1) A measure of how much radiation is absorbed when traveling through a medium
(such as the atmosphere of a star or the interstellar medium) from the source to a
given point. It depends on the type of medium and the frequency of radiation.
It is defined as a dimensionless quantity
dτλ = κλ ρ dx,
where κλ is the
extinction coefficient, ρ the density, and dx the path length.
optical double star
setâre-ye dotâyi-ye didgâni
Fr.: étoile double optique
A pair of stars that lie close to each other in the sky by chance, but are not physically associated, in contrast to a true → binary star.
→ optical; → double star.
Fr.: fibre optique
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote internal reflection. It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.
Fr.: illusion d'optique
A perception of visual stimuli in which what is perceived is in a way different from the way it is in reality. Same as visual illusion.
Fr.: instrument optique
An instrument that either processes light waves to enhance an image or analyzes light waves to determine one of a number of characteristic properties.
→ optical; → instrument.
Fr.: jet optique
An → astrophysical jet which is visible in the optical range of the electromagnetic radiation.
Fr.: aplatissement optique
(polar flattening) The ratio of the difference between equatorial and polar diameters to the equatorial diameter. A sphere has an oblateness of 0; an infinitely thin disk has an oblateness of 1 (Ellis et al., 2007, Planetary Ring Systems, Springer).
→ optical; → oblateness.
râh-e nuri (#)
Fr.: chemin optique
In → geometric optics, the distance a light ray would travel in a vacuum in the same time it travels from one point to another, a specified distance, through one or more optical media.
pulsâr-e nuri, tapâr-e ~
Fr.: pulsar optique
A member of a rare class of pulsars, such as the → Crab pulsar and → Vela pulsar, which can be detected in the visible spectrum.
Fr.: pompage optique
A process in which light energy is used to raise electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction, to pump the active laser medium so as to achieve population inversion. The technique was developed by 1966 Nobel Prize winner Alfred Kastler in the early 1950's.
râžmân-e nuri, ~ nurik
Fr.: système optique
A collection of lens, prisms, mirrors, and/or other devices, placed in some specified configuration, to act on light (reflect, refract, disperse, polarize, etc.) and perform some definite optical function.
Fr.: épaisseur optique
Same as → optical depth.
optical transfer function (OTF)
karyâ-ye tarâvaž-e nuri
Fr.: fonction de transfert optique
The function that provides a full description of the imaging quality of an optical system. A combination of the → modulation transfer function (MTF) and the → phase transfer function (PTF) , the OTF describes the spatial (angular) variation as a function of spatial (angular) frequency.
Fr.: fenêtre optique
The optical portion of the electromagnetic spectrum that passes through the atmosphere all the way to the ground.
Adverb of → optical.
→ optical + -ly.
Nurâné, from nur, → light, + -âné "-ly;" nurikâné, from nurik, → optical, + -âné "-ly."
Fr.: optiquement actif
Relating to → optical activity.
nurâné setabr, nurikâné ~
Fr.: optiquement épais
The qualifier of a medium in which the → optical depth is large, significantly larger than 1.
optically thick wind
bâd-e nurâné setabr
Fr.: vent optiquement épais
A wind with the → sonic point located at large optical depth for continuum. In particular, → Wolf-Rayet star winds are → optically thick. However, the outer parts of W-R winds are → optically thin for continuum, and in those regions the matter flow is driven by the same mechanism as in the winds of OB stars.