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.
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."
"daryâ-ye mâh" (#)
Fr.: mer lunaire
An area on the surface of the → Moon that appears darker and smoother than its surroundings. Once thought to be seas, lunar maria are now known to be basaltic basins created by volcanic → lava floods; plural maria.
"daryâhâ-ye mâh" (#)
Fr.: mer lunaire
Plural of → lunar mare.
→ lunar mare.
jerm-e mâh (#), ~ mâng
Fr.: masse lunaire, masse de la Lune
The mass of the → Moon, which is 7.35 x 1022 kg, about 1/81 of the Earth's mass.
Fr.: mois lunaire
gereh (#), gowzahr (#)
One of the two points of intersection of the orbit of the Moon with the plane of → ecliptic. Indeed, the lunar orbit is tilted by about 5 degrees relative to the ecliptic. The revolution period of a lunar node in ecliptic is 18.61 years. Due to perturbation by the Sun, the lunar nodes slowly regress westward by 19.3° per year. See also → ascending node; → descending node.
lunar orbit node
gereh-e madâri-ye mâh
Fr.: nœud de l'orbite lunaire
Same as → lunar node.
Fr.: parallaxe lunaire
The apparent shift in the → Moon's position relative to the background stars when observed from different places on Earth. The first parallax determination was for the Moon, by Hipparchus (150 B.C.). He determined that one-fifth of the Sun's angular diameter corresponded to the lunar parallax between Hellespont and Alexandria.
simâ-ye mâh (#)
Fr.: phase de la lune
One of the various changes in the apparent shape of the Moon, because as the Moon orbits the Earth different amounts of its illuminated part are facing us. The phases of the Moon include: the → new moon, → waxing crescent, → first quarter, → waxing gibbous, → full moon, → waning gibbous, → last quarter, → waning crescent, and → new moon again.
Fr.: sonde lunaire
A probe for exploring and reporting on conditions on or about the Moon.
Fr.: éloignement de la lune
The process whereby the → Moon gradually moves out into a slightly larger orbit. The → gravitational attraction of the Moon on the → Earth creates two ocean → tidal bulges on the opposite sides of our planet. The Earth rotates faster than the Moon revolves about the Earth. Therefore, the tidal bulge facing the Moon advances the Moon with respect to the line joining the centers of the Earth and the Moon. The Moon's gravity pulls on the bulge and slows down the → Earth's rotation. As a result, the Earth loses → angular momentum and the days on Earth are gradually increasing by 2.3 milliseconds per century. Since the angular momentum in the → Earth-Moon system is conserved, the Earth must impart the loss in its own angular momentum to the Moon's orbit. Hence, the Moon is being forced into a slightly larger orbit which means it is receding from the Earth. However, eventually this process will come to an end. This is because the Earth's own rotation rate will match the Moon's orbital rate, and it will therefore no longer impart any angular momentum to it. In this case, the planet and the Moon are said to be tidally locked (→ tidal locking). This is a stable situation because it minimises the energy loss due to friction of the system. Long ago, the Moon's own rotation became equal to its orbital period about the Earth and so we only see one side of the Moon. This is known as → synchronous rotation and it is quite common in the solar system. The Moon's average distance from Earth in increasing by 3.8 cm per year. Such a precise value is possible due to the Apollo laser reflectors which the astronauts left behind during the lunar landing missions (Apollo 11, 14, and 15). Eventually, the Moon's distance will increase so much that it will be to far away to produce total eclipses of the Sun.
sangpuš-e mâh, ~ mângi
Fr.: régolithe lunaire
The loose, fragmentary material on the Moon's surface. The lunar regolith has resulted from → meteorite collisions all along the Moon's history. It is the → debris thrown out of the → impact craters. The composition of the lunar regolith varies from place to place depending on the rock types impacted. Generally, the older the surface, the thicker the regolith. Regolith on young → maria may be only 2 meters thick; whereas, it is perhaps 20 meters thick in the older → highlands.