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.
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.
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."