angle of refraction
zâviye-yé šekast (#)
Fr.: angle de réfraction
The angle between the direction in which a ray is refracted and the normal to the refracting surface.
Fr.: réfraction astronomique
Fr.: réfraction atmosphérique
The shift in apparent direction of a celestial object caused by the bending of light while passing through the Earth's atmosphere. Since the density of the atmosphere decreases with altitude, the starlight will bend more as it continues down through the atmosphere. As a result, a star will appear higher in the sky than its true direction.
Fr.: refraction différentielle
A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction.
Fr.: double réfraction
Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.
doubly refracting crystal
bolur-e šakst-e dotâyi
Fr.: cristal à double réfraction
A → transparent → crystalline substance (such as calcite, quartz, and tourmaline) that is → anisotropic relative to the → speed of light. A ray incident normally on such crystals is broken up into two rays in traversing the crystal, → ordinary ray and → extraordinary ray.
Fr.: réfracteur de Fraunhofer
The first modern refracting telescope which had an outstanding quality. It was built in 1824 by Fraunhofer for the Russian Imperial Observatory in Dorpat, now Tartu in Estonia. It had a 23-cm → achromatic lens and a German-type → equatorial mounting driven by a clockwork. Wilhelm Struve (1793-1864) used the refractor to observe many → visual binaries, and attempted to measure the distances of stars through their visual → parallaxes. He also obtaibned accurate values for the diameters of the → Galilean satellites of → Jupiter.
Named after Joseph von Fraunhofer (1787-1826), German optician and physicist; → refractor.
Fr.: réfraction géodésique
The limiting case of → astronomical refraction when the light path is entirely within the Earth's atmosphere.
šekast-e ofoqi (#)
Fr.: réfraction horizontale
The angular distance of an object below the horizon when it appears to lie on the horizon.
index of refraction
Fr.: indice de réfraction
Same as → refractive index.
law of refraction
qânun-e šekast (#)
Fr.: loi de réfraction
One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.
To alter the course of a wave of light, sound, etc. when the wave crosses the boundary between this medium and another through which it travels at a different speed.
From L. refractus, p.p. of refringere, → refraction.
Verb of šekast, → refraction.
partow-e šekasté (#)
Fr.: rayon réfracté
A → light ray that undergoes a change of velocity and direction, as a result of interaction with the material medium in which it travels.
Fr.: réfraction; à réfraction
manšur-e šekastgar (#)
Fr.: prisme réfractant
A prism that is used as a dispersing element in a spectrograph.
teleskop-e šekasti (#), durbin-e ~ (#)
Fr.: lunette astronomique
A telescope in which an image is formed by the refraction of light through a lens or lens system.
1) Optics: The change of direction which a beam of light undergoes as it
enters a medium of different → refractive index.
From L.L. refractionem (nominative refractio) "a breaking up," from L. refractus, p.p. of refringere "to break up," from re- "back" + combining form of frangere "to break," from PIE base *bhreg- "to break" (cf. Goth. brikan, O.E. brecan "to break;" Lith. brasketi "crash, crack").
Šekast, past stem of šekastan "to break, split;" Mid.Pers. škastan "to break;" Av. scind-, scand "to beak, cleave;" Proto-Iranian *skand- "to break, cleave;" PIE sken- "to cut off."
Fr.: indice de réfraction
Of any optical medium, the ratio of the → speed of light in vacuum (c) to that in the medium (v): n = c/v. The refractive index for vacuum, by definition, is 1. The refractive index of air is 1.00029 at standard temperature (25 °C) and pressure (1 atm). The refractive index of a medium depends on the wavelength of refracted wave. With light waves, n increases as the wavelength decreases. → Snell's law can be used to derive n. Same as → index of refraction.
Same as → refracting telescope.
Agent noun of refract, → refraction.
From refract, → refraction + adj. suffix -ory.
Sarkeš "refractory, disobedient, rebellious, stubborn,"
literally "withdrw, remove head," from sar
"head" (variants soru, sorun "horn,"
karnâ "a trumpet-like wind instrument," variant sornâ "a wind instrument;"
Mid.Pers. sar "head," sru "horn;" Av. sarah- "head,"
srū- "horn, nail;" cf. Skt. śiras- "head, chief;"
Gk. kara "head," karena "head, top," keras "horn;"
L. cornu "horn," cerebrum "brain;"
P.Gmc. *khurnaz (Ger. Horn, Du. horen;
cognate with E. horn, as above, from PIE *ker- "head, horn;"
O.E. horn "horn of an animal," also "wind instrument;"
E. horn); PIE base *ker-
"head, horn, top, summit")
+ keš present stem of kešidan, kašidan
"to draw; withdraw, remove" (dialectal Yaqnavi xaš "to draw," Qomi xaš
"streak, stria, mark," Lori kerr "line;"
Av. karš- "to draw; to plow," karša-
"furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;"
cf. Skt. kars-, kársati "to pull, drag, plow;"
Gk. pelo, pelomai "to move, to bustle;" PIE base kwels-