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.
Fr.: efficacité lumineuse
A measure indicating the ability of a light source to emit visible light using a given amount of → power. It is a ratio of the visible energy emitted to the power that goes into the bulb from the electrical line.
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).
Fr.: éclipse de lune
The → darkening of the → Moon which occurs when the Moon enters the → umbra of the → Earth's shadow. This phenomenon can occur only when the → full Moon is near one of the → lunar nodes of its → orbit around the Earth. There will be a → total eclipse if the entire Moon enters the umbra, otherwise the eclipse will be partial when the Moon is somewhat to the north or south of the node and does not cross the shadow entirely. During the eclipse the Moon looks more or less dark, depending especially on the transparency of the Earth's → atmosphere. The → refraction of Sun's light through the atmosphere sometimes gives a red color to the eclipsed Moon. Colored fringes can be seen around the shadow edge during → partial eclipses. Because an eclipse of the Moon is due to the cutting off of the Sun's light, it is visible from the entire hemisphere where the Moon is above the horizon. The maximum duration of a total lunar eclipse, when the Moon passes through the shadow centrally, is 1h 47m (M.S.: SDE).
lunar ecliptic limit
hadd-e hurpehi-ye mâh
Fr.: limite écliptique de la Lune
The farthest distance from a → lunar orbit node within which, if the Moon happens to be at full, a lunar eclipse may occur. The lunar ecliptic limit extends about 12° on each side of the node.
Fr.: exosphère lunaire
An extremely thin gathering of gas surrounding the → Moon. It is made up of → atoms and → ions generated at the Moon's surface by interaction with → solar radiation, → plasma in the Earth's → magnetosphere, or → micrometeorites.
lunar far side
ruy-e dur-e mâng
Fr.: face cachée de la Lune
The Moon's hemisphere which is not visible from the Earth. The Moon always shows the same face to the Earth, because Earth and Moon are → tidally locked. This means that the period of → lunar rotation on it axis is the same as its sidereal revolution period around the Earth (→ sidereal month). In other words, the Moon is in → synchronous rotation with the Earth. As a result, the same side always faces the Earth. To be more precise, taking the lunar → libration into account, the Moon presents about 59% of its surface to Earth. → libration in longitude, → libration in latitude, → physical libration, → geometrical libration.
Fr.: géologie lunaire
Fr.: hauts plateaux lunaires
lunar horizon glow
foruq-e ofoq-e mâh
Fr.: éclat de l'horizon lunaire
A very bright crescent of light glowing on the lunar horizon at → sunset or just before → sunrise. It has been suggested that → lunar dust is transported electrically high into sky, allowing sunlight to scatter and create glows. On the day side of the → Moon, solar → ultraviolet radiation is strong enough to kick → electrons from → dust grains in the lunar soil. Removal of electrons, which have a negative electric charge, leaves the dust with a positive electric charge. Since like charges repel, the positively charged dust particles get pushed away from each other, and the only direction not blocked by more dust is up. In the 1960s, Surveyor probes filmed a glowing cloud floating just above the lunar surface during sunrise. Later, Apollo 17 astronaut Gene Cernan, while orbiting the Moon, recorded a similar phenomenon at the sharp line where lunar day meets night, called the → terminator.
manzel-e mâh (#)
Fr.: maison lunaire
One of the 28 divisions of the sky, identified by the prominent stars in them, that the Moon passes through during its monthly cycle, as used in ancient Chinese, Hindu, and Arab astronomy/astrology.
From O.Fr. mansion, from L. mansionem (nom. mansio) "a staying, a remaining, night quarters, station," from manere "to stay, abide" (Fr. maison, ménage; E. manor, mansion, permanent); cf. Pers. mân "house, home," mândan "to remain, stay, relinquish, leave;" Mid.Pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" Gk. menein "to remain;" PIE base *men- "to remain, wait for."
Manzel, from Ar. "dwelling, habitation, mansion."