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.
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.
Capable of, suitable for, or exhibiting luminescence.
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.
Verbal noun of → luminous.
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.
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.
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.
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).
tâbân (#), tâbeši (#)
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)
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.
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 infrared galaxy (LIRG)
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.
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.
mâdde-ye tâbân (#)
Fr.: matière lumineuse
Ordinary baryonic matter that can emit electromagnetic radiation, as opposed to → dark matter.
luminous red nova (LRN)
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.
mângi (#), mahi (#)
Of or pertaining to the moon.
From O.Fr. lunaire, from L. lunaris "of the moon," from luna "moon" (with capital L) "moon goddess," from *leuksna- (cf. O.C.S. luna "moon," O.Pruss. lauxnos "stars," M.Ir. luan "light, moon"), from the same source as lux, lumen "light;" cognate with Pers. ruz, → day, rowšan "bright, clear."
Mâh and mâng in Pers. are variants of the same term, the dominant form being
mâh, while mâng (Av. from, see below) is used in classical literature
as well as in some dialects: Tabari, Kurd. mâng, Laki, Tâti, Taeši
Sangesari mung; Mid.Pers. mâh "moon, month;" O.Pers. māha-
"moon, month;" Av. māh- "month, moon," also māwngh-; cf.
Skt. mās- "moon, month;" Gk.
mene "moon," men "month;" L. mensis "month;"
O.C.S. meseci, Lith. menesis "moon, month;" O.Ir. mi,
Welsh mis, Bret. miz "month;"
O.E. mona; E. moon, month; Ger. Mond, Monat;
Du. maan; PIE base *me(n)ses- "moon, month."
Fr.: calendrier lunaire
lâvak-e mâh, ~ mângi, kandâl-e ~
Fr.: cratère lunaire
A → crater on the surface of the Moon.
ruz-e mâng, ~ mângi
Fr.: jour lunaire
The interval between two successive sunrises for an observer standing on the Moon. This is not the rotational period of the Moon, because the Moon-Earth system has moved round the Sun during that period. It is equal to the length of a → synodic month (29.5306 days).
Fr.: poussière lunaire
A fine, powder-like dust covering the Moon's surface. → regolith. It is formed when meteoroids crash on the Moon's surface, heating and pulverizing rocks, which contain silica and metals. Since there is no wind or water to smooth rough edges, the tiny grains are sharp and jagged, and cling to nearly everything. Their main chemical compositions are SiO2 (about 45%) and Al2O3 (about 15%). The dust grains have an average size of 19 microns (40% smaller than hair).