angle of reflection
zâviye-ye bâztâb (#)
Fr.: angle de réflexion
The angle between the reflected ray and the normal to the reflecting surface.
Fr.: réflexion diffuse
Reflection of light from a rough or granular surface, which takes place in all directions due to the microscopic irregularities of the interface; opposed to → specular reflection.
Foucault's Marseille reflector
bâztâbgar-e Foucault-ye Marseille
Fr.: réflecteur marseillais de Foucault
The first functioning → reflecting telescope with a silvered glass mirror. It was built by Léon Foucault in 1826 for the Marseille Observatory. The mirror of 80-cm in diameter (f/d = 5) had an excellent quality. The telescope was used for a century as a visual instrument. Edouard Stéphan (1837-1923) used it from 1871 to 1884 to find 800 high-brightness galaxies, among which the → Stephan's Quintet. From 1906 to 1962 the telescope was used by Robert Jonckheere (1888-1927) to discover 3,350 new binary stars. In 1873, following an idea of Hippolyte Fizeau (1819-1896), Stéphan attempted to use it as an → interferometer to measure the diameter of a number of stars. In 1914 Charles Fabry (1867-1945) and Henri Buisson (1873-1944) used the telescope to obtain the first astronomical Fabry-Pérot interferogram, on the → Orion Nebula.
After the French physicist and optician Léon Foucault (1819-1868); Marseille (Observatory), the second largest city of France, located on the south east coast of the Mediterranean Sea, from L. Massalia, from Gk. Massalia; → reflector.
law of reflection
qânun-e bâztâb (#)
Fr.: loi de réflexion
One of the two laws governing reflection of light from a surface: a) The → incident ray, normal to surface, and reflected ray lie in the same plane. b) The → angle of incidence (with the normal to the surface) is equal to the → angle of reflection.
To throw or bend back from a surface, specially light, sound, or heat.
M.E. reflecten, from L. reflectere "to bend back," from → re- "back" + flectere "to bend."
Bâztâbidan, from bâz-, → re- + tâbidan, variants tâftan "to shine," tafsidan "to become hot;" Mid.Pers. tâftan "to heat, burn, shine;" taftan "to become hot;" Parthian t'b "to shine;" Av. tāp-, taf- "to warm up, heat," tafsat "became hot," tāpaiieiti "to create warmth;" cf. Skt. tap- "; to heat, be/become hot; to spoil, injure, damage; to suffer," tapati "burns;" L. tepere "to be warm," tepidus "warm;" PIE base *tep- "to be warm."
1) Same as → reflection factor.
From → reflect + -ance
Bâztâbâyi, verbal noun from adj./agent noun bâztâbâ "reflecting."
partow-e bâztâbidé (#)
Fr.: rayon réfléchi
A → light ray that is reflected from a surface.
Fr.: cercle à réflexion
An instrument for measuring angular distances, based on the same principle as the → octant, but with a full circular limb divided into 720°. It was invented in 1752 by the German astronomer Johann Tobias Mayer (1723-1762) to improve on the octant which often gave wrong results because of incorrect graduations. The instrument consisted of an index arm and a small telescope, both pivoted centrally. In practice, the index arm is first set to zero, and the telescope rotated until the two images of a star are seen in coincidence (the one directly, the other by double reflection). Then the index arm is freed, and rotated until the other object is seen in coincidence after double reflection. The angle has now been measured, but the double operation is repeated several times, and the final angle divided by the number of repetitions to find a mean value. Hence, the instrument was sometimes called a "repeating circle." The reflecting circle had little success because it was heavy and uncomfortable to use. Its improved form is called → Borda circle.
teleskop-e bâztâbi (#), durbin-e ~ (#)
Fr.: télescope réflecteur
A telescope in which the image is produced by reflection of light by a concave mirror.
Verbal noun of → reflect.
hamgar-e bâztâb (#)
Fr.: coefficient de réflexion
The ratio given by the → amplitude (or energy) of a reflected wave divided by the amplitude (or energy) of the incident wave.
Fr.: facteur de réflexion
The ratio of total flux that is reflected from a surface to the incident flux. Also called reflectance, reflectivity.
Fr.: nébuleuse par réflexion
A type of nebula that is visible from its reflection of starlight. Bright stars near reflection nebulae emit light into the region that is reflected by the large amount of dust there. The size of the dust grains causes blue light to be reflected more efficiently than red light, so these reflection nebulae frequently appear blue in color.
Fr.: réfléchissant, réflecteur
That reflects; reflecting. Of or pertaining to reflection.
From → reflect + -ive a suffix of adjectives and nouns of adjectival origin.
Bâztâbi adj. of bâztâb, → reflection.
Fr.: réflexion régulière
bâztâb-e âyenevâr (#)
Fr.: réflexion spéculaire
The reflection of light waves in which the reflected waves travel in a definite direction, and the directions of the incident and reflected waves make equal angles with a line perpendicular to the reflecting surface. Same as → regular reflection; opposite of → diffuse reflection.
From L. specularis, from speculum "mirror;" → reflection.
total internal reflection
bâztâb-e hamâk-e daruni
Fr.: réflexion totale interne
A phenomenon occurring when a light ray traveling cross an → interface from a higher → refractive index medium to a lower refractive index medium hits the interface at an angle larger than the → critical angle. In these conditions the light will not pass through to the second → medium at all. Instead, all of it will be reflected back into the first medium.