An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 474
lower culmination
  بالست ِ زیرین   
bâlest-e zirin

Fr.: culmination inférieure   

The instant of culmination when the star passes between the pole and the horizon, having an hour angle of 12h. Lower culmination for non-circumpolar objects occur below the horizon and is thus unobservable. Same as → inferior culmination. See also → upper culmination.

lower; → culmination.

lower mantle
  گوشته‌ی ِ زیرین   
gušte-ye zirin

Fr.: manteau inférieur   

The part of the Earth's → mantle extending from about 660 km below the surface to above the → outer core at about 2,900 km.

lower; → mantle.

LS coupling
  جفتش ِ LS، جفسری ِ ~   
jofteš-e LS, jafsari-ye ~

Fr.: couplage LS   

Same as → Russell-Saunders coupling.

L referring to the total → orbital angular momentum and S to the total → spin angular momentum; → coupling.

lukewarm
  ولرم   
velarm (#)

Fr.: tiède   

Moderately warm; tepid.

M.E. lukewarme "tepid," from luke "tepid," of unknown origin, + → warm.

Velarm "lukewarm, tepid," of unknown origin.

lumen
  لومن   
lumen (#)

Fr.: lumen   

The SI unit of luminous flux, equal to the luminous flux emitted per unit solid angle by a standard point source having a luminous intensity of 1 candela. → candela.

L. lumen (gen. luminis) "light," from lucere "to shine," related to lux "light," lucidus "clear," luna, "moon;" Fr. lumière "light;" cf. Pers. ruz "day," rowšan "bright, clear," rowzan "window, aperture;" foruq "light," afruxtan "to light, kindle;" Mid.Pers. rôšn "light; bright, luminous," rôc "day;" O.Pers. raucah-rocânak "window;" O.Pers. raocah- "light, luminous; daylight;" Av. raocana- "bright, shining, radiant;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness."

Lumen loanword, as above.

luminance
  تابانی   
tâbâni (#)

Fr.: luminance   

The luminous intensity in a given direction of a small element of surface area divided by the orthogonal projection of this area onto a plane at right angle to the direction. It is measured in candelas per square meter. Luminance is often called surface brightness of the object.

From lumin-, combining form of → lumen "light," + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.

Tâbâni, from tâbidan "to shine," → luminous.

luminescence
  فروزستی   
foruzesti

Fr.: luminescence   

The emission of light at low temperatures by any process other than → incandescence, where a substance emits light without being strongly heated. Luminescence is a collective term for different phenomena, for example: → phosphorescence, → fluorescence, → chemiluminescence, → photoluminescence.

From lumin-, from → lumen; → -escence.

luminescent
  فروزست   
foruzest

Fr.: luminescent   

Capable of, suitable for, or exhibiting luminescence.

From lumin-, from → lumen; → -escent.

luminosity
  تابندگی   
tâbandegi (#)

Fr.: luminosité   

The → total → brightness of a star or other astronomical object. It is expressed in watts and represents the total amount of → energy that the object radiates each → second over all wavelength regions of the → electromagnetic spectrum. Because this quantity is independent of distance, it is an → intrinsic brightness.
See also:
absolute luminosity, → anomalous luminosity effect, → bolometric luminosity, → color-luminosity diagram, → Eddington luminosity, → H II region luminosity, → intrinsic luminosity, → luminosity class, → luminosity distance, → luminosity function, → luminosity problem, → mass-luminosity ratio, → mass-luminosity relation, → peak luminosity, → period-luminosity relation, → solar luminosity, → stellar luminosity, → wind luminosity.

Verbal noun of → luminous.

luminosity class
  رده‌ی ِ تابندگی   
rade-ye tâbandegi (#)

Fr.: classe de luminosité   

A classification of stellar spectra according to luminosity for a given → spectral type. The luminosity class is an indication of a star's → surface gravity. It is shown by a Roman numeral as follows: I (→ supergiants), II (bright → giants), III (normal giants), IV (→ subgiants), and V (→ dwarf stars, or → main-sequence stars). Luminosity classes VI (→ subdwarfs) and VII (→ white dwarfs) are rarely used. Subclasses a, b, and c are especially used for supergiants, while the most luminous → hypergiants are assigned luminosity class Ia-0.

luminosity; → class.

luminosity distance
  اپست ِ تابندگی   
apast-e tâbandegi

Fr.: distance de luminosité   

1) Distance derived by comparison of → observed and → intrinsic luminosities. If an object has a known luminosity L, and the observed flux is S, the luminosity distance is defined by DL = (L/4πS)1/2.

2) In cosmology, the → expansion of the Universe results in a diminution of the photon flux and the above equation fails. The reason is that for a homogeneous and isotropic Universe (→ Robertson-Walker metric), the luminosity decreases by a factor (1 + z)4. Therefore, the luminosity distance is related to the → angular diameter distance (DA) by: DL = (1 + z)2.DA.

luminosity; → distance.

luminosity function
  کریا‌ی ِ تابندگی   
karyâ-ye tâbandegi

Fr.: fonction de luminosité   

Number → distribution of → stars or galaxies (→ galaxy) with respect to their → absolute magnitudes. The luminosity function shows the → number of stars of a given intrinsic luminosity (or the number of galaxies per integrated magnitude band) in a given → volume of space.

luminosity; → function.

luminosity problem
  پراسه‌ی ِ تابندگی   
parâse-ye tâbandegi

Fr.: problème de luminosité   

Low-mass → protostars are about an order of magnitude less luminous than expected. Two possible solutions are that → low-mass stars form slowly, and/or protostellar → accretion is episodic. The latter accounts for less than half the missing luminosity. The solution to this problem relates directly to the fundamental question of the time required to form a low-mass star (McKee & Offner, 2010, astro-ph/1010.4307).

luminosity; → problem.

luminous
  تابان، تابشی   
tâbân (#), tâbeši (#)

Fr.: lumineux   

Radiating light or other types of electromagnetic energy.

From L. luminosus "shining, full of light," from → lumen (gen. luminis) "light," related to lucere "to shine."

Tâbân "luminous," verbal adj. of tâbidan "to shine," variants tâftan "to shine," tafsidan "to become hot," related to tâb "heat, burning; heated iron; torment," âftâb "sunshine," tâbé "frying-pan," tab "fever;" dialect of Gaz tôu-, tôwâ "to shine;" Khotanese ttav- "to be hot;" Mid.Pers. tâftan "to heat, burn, shine;" taftan "to become hot;" Parthian tâb- "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."

Luminous Blue Variable (LBV)
  ورتنده‌ی ِ آبی ِ تابان   
vartande-ye âbi-ye tâbân

Fr.: variable bleue lumineuse   

A high-luminosity variable star, which represents a transition phase in the life of a massive star when it evolves off the main sequence to become a supernova. Only about a dozen confirmed LBVs are presently known in our Galaxy. → Hubble-Sandage variable.

luminous; → blue; → variable.

luminous flux
  شار ِ تابشی   
šâr-e tâbeši (#)

Fr.: flux lumineux   

A measure of the rate of flow of luminous energy, evaluated according to its ability to produce a visual sensation. It is measured in lumens.

luminous; → flux.

luminous infrared galaxy (LIRG)
  کهکشان ِ فروسرخ ِ تابان   
kahkešân-e forusorx-e tâbân

Fr.: galaxie lumineuse en infrarouge   

A galaxy that emits most of its energy in the infrared and whose infrared luminosity (in the 8-1000 µm range) is more than 1011 solar luminosities. → ultraluminous infrared galaxy.

luminous; → infrared; → galaxy.

luminous intensity
  درتنویی ِ تابشی   
dartanuyi-ye tâbeši

Fr.: intensité lumineuse   

A measure of the amount of light that a point source radiates in a given direction. It is expressed by the luminous flux per unit leaving the source in the direction per unit of solid angle.

luminous; → intensity.

luminous matter
  مادّه‌ی ِ تابان   
mâdde-ye tâbân (#)

Fr.: matière lumineuse   

Ordinary baryonic matter that can emit electromagnetic radiation, as opposed to → dark matter.

luminous; → matter.

luminous red nova (LRN)
  نو‌اختر ِ سرخ ِ تابان   
now-axtar-e sorx-e tâbân

Fr.: nova rouge lumineuse   

A stellar explosion thought to be caused by the → merger of stars in a → binary system. They are characterized by a distinct red color, and a → light curve that lingers with resurgent brightness in the → infrared. The luminosity of the explosion is between that of a → supernova and a → nova.

luminous; → red; → nova

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