Lune
| Caractéristiques de l'orbite | |||||||
|---|---|---|---|---|---|---|---|
| Rayon moyen | 384,400 km | ||||||
| Excentricité | 0.0549 | ||||||
| Période de révolution | 27j 7h 43.7m | ||||||
| Inclinaison | 5.1454° | ||||||
| Est le satellite de | la Terre | ||||||
| Caractéristiques physiques | |||||||
| Diamètre équatorial | 3,474.8 km | ||||||
| Superficie | 38 million km2 | ||||||
| Masse | 7.349 × 1022 kg | ||||||
| Densité moyenne | 3.34 g/cm3 | ||||||
| Gravité en surface | 1.62 m/s2 | ||||||
| Période de rotation | 27j 7h 43.7m | ||||||
| Inclinaison axiale | 1.5424° | ||||||
| Albedo | 0.12 | ||||||
| temp. de surface |
|
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| Caractéristiques Atmospherique | |||||||
| Pression atmosphérique | 3 × 10-13kPa | ||||||
| Hélium | 25% | ||||||
| Néon | 25% | ||||||
| Hydrogène | 23% | ||||||
| Argon | 20% | ||||||
| Méthane Dioxyde de carbone | traces | ||||||
Cette page se réfère à la Lune terrestre. Pour les autres lunes du système solaire, allez voir à satellite naturel. Des informations sont également disponibles sur les missions d'explorations spatiales automatisées du programme Luna.
La Lune est le seul satellite naturel de la Terre, et est occasionnellement appelé Luna (mot latin signifiant lune) pour la distinguer du mot d'usage général "lune".
La Lune est différenciée des satellites des autres planètes par sa première lettre majuscule; les autres lunes du système solaire sont décrites dans l'article satellite naturel.
Cette image couleur de la Lune a été prise par la sonde Galileo le 9 décembre 1990 à 17h35 GMT, à une distance d'environ 563,000 km. Ce cliché est composé d'images monochromes prisent à travers des filtres violet, rouge et proche infrarouge. The concentric, circular Orientale basin, 600 miles across, is near the center; la face proche de la Terre est à droite, la face éloignée à gauche. En haut à droite se trouve le grand et sombre [Oceanus Procellarum]]; en-dessous la plus petite Mare Humorum. Celle-ci, comme la petite et sombre Mare Orientale dans le centre du bassin, se sont formées il y a 3 milliards d'années à partir de coulées de lave basaltique. At the lower left, among the southern cratered highlands of the far side, is the South-Pole-Aitken basin, similar to Orientale but twice as great in diameter and much older and more degraded by cratering and weathering. The cratered highlands of the near and far sides and the Maria are covered with scattered bright, young ray craters. click here for full-sized image
Caractéristiques Physiques
Comme la période de rotation de la Lune est exactement la même que sa période orbitale, nous voyons toujours la même face de la Lune pointée vers la Terre. This synchronicity is a result of tidal friction slowing down the Moon's rotation in its early history, a process known as tidal locking. As a result of this tidal locking, the Earth's rotation is also gradually being slowed down by the Moon, and the Moon is slowly receding from the Earth as the Earth's rotational momentum is transferred to the Moon's orbital momentum. The gravitional attraction that the Moon exerts on the Earth is the cause of tides in the sea. Tidal flow is synchronised to the Moon's orbit around the Earth.
The Earth and Moon orbit about their common center of mass, which lies inside the Earth about 4700 km from the Earth's center. Since the common center of mass of the Earth-Moon system (the barycenter) is located within Earth, Earth's motion is more commonly described as a "wobble". When viewed from Earth's North pole, the Earth and Moon rotate counter clockwise about their axes, Moon orbits Earth counter-clockwise and Earth orbits the Sun counter-clockwise.
The Moon's orbital plane about the Earth is inclined by 5 degrees with respect to the Earth's orbital plane about the Sun (the ecliptic plane). The Moon's orbital plane along with its spin axis rotates clockwise with a period of 18.6 years, always maintaining the 5 degree inclination. The points where the Moon's orbit crosses the ecliptic are called the lunar "nodes": the North (or ascending) node is where the Moon crosses to the North of the ecliptic; the South (or descending ) node where it crosses to the South. Solar eclipses occur when a node coincides with the new Moon; lunar eclipses when a node coincides with the full Moon.
The inclination of the Moon's orbit makes it rather unlikely that the Moon formed along with the Earth or was captured later; its origin is the subject of strong scientific debate. The most accepted theory states that the Moon originated from the collision between the young Earth and an impactor the size of Mars and was formed from material ejected from Earth as a result of the collision. This is called the Giant Impact theory. New simulations published in August 2001 support this theory . This theory is also corroborated by the fact that the Moon has all the same minerals as the Earth, albeit in different proportions.
The Moon exhibits different phases as the relative positions of the Sun, Earth and Moon change, appearing as the full moon when the Sun and Moon are on opposite sides of the Earth, and becoming invisible as the new moon when they are on the same side. The time between two full moons is 29.5 days; it is longer than the time it takes the Moon to orbit the Earth since the Earth-Moon system is orbiting the Sun. The phases are not created by the shadow of the Earth on the moon; instead, they are a result of our seeing only part of the illuminated half of the Moon. In the Northern hemisphere, if the right side of the Moon is dark, the light part is shrinking: the Moon is waning (moving towards a new Moon). If the left side is dark, the Moon is waxing (moving towards a full Moon). The acronym mnemonic "DOC" represents this ("D" is the waxing Moon; "O" the full moon; and "C" the waning moon). In the Southern hemisphere, this is reversed, and the mnemonic is "COD". A french mnemonic is that the waxing moon at its first "premier" quarter phase looks like a 'p', and the waning moon at its last "dernier" quarter looks like a 'd'. One more (Northern hemisphere) mnemonic, which works for most Romance languages, says that the Moon is a liar: it spells "C", as in crescere (Italian for "to grow") when it wanes, and "D" as in decrescere ("decrease") when it waxes.
By what can only be a truly extraordinary coincidence, the apparent size of the Moon as seen from the Earth is almost exactly the same as the apparent size of the Sun, so that total solar eclipses are possible where the Moon almost completely covers the Sun and the solar corona becomes visible to the naked eye.
The Moon (and also the Sun) appear larger when close to the horizon. This is a purely psychological effect (atmospheric refraction and its larger distance actually causes the image of the Moon near the horizon to be slightly smaller); it is assumed that size judgments for overhead objects were not important during evolution of the cognitive apparatus and are therefore inaccurate. [1]
Various lighter and darker colored areas create the patterns seen by different cultures as the Man in the Moon, the rabbit and the buffalo, amongst others. Craters and mountain chains are also prominent lunar features. The dark and relatively featureless lunar plains are called maria, latin for seas, since they were believed by ancient astromomers to be water-filled seas. The lighter-colored highlands are called terrae.
Composition
Il y a plus de 4.5 milliards d'année, la surface de la Lune était un océan de magma liquide. Scientists think that one component of lunar rocks, KREEP (K-potassium, Rare Earth Elements, and P-phosphorous), represents the last chemical remnant of that magma ocean. KREEP is actually a composite of what scientists term "incompatible elements": those which cannot fit into a crystal structure and thus were left behind, floating to the surface of the magma. For researchers, KREEP is a convenient tracer, useful for reporting the story of the volcanic history of the lunar crust and chronicling the frequency of impacts by comets and other celestial bodies.
The lunar crust is composed of a variety of primary elements, including uranium, thorium, potassium, oxygen, silicon, magnesium, iron, titanium, calcium, aluminum and hydrogen. When bombarded by cosmic rays, each element bounces back into space its own radiation, in the form of gamma rays. Some elements, such as uranium, thorium and potassium, are radioactive and emit gamma rays on their own. However, regardless of what causes them, gamma rays for each element are all different from one another -- each produces a unique spectral "signature," detectable by a spectrometer. A complete global mapping of the Moon for the abundance of these elements has never been performed.
Over time, comets and meteorites continually bombard the Moon. Water-rich meteorites and comets, largely water ice, may leave significant traces of water on the lunar surface. Energy from sunlight splits much of this water into its constituent elements hydrogen and oxygen, both of which usually fly off into space immediately. Some water molecules, however, may have literally hopped along the surface and gotten trapped inside enormous craters -some 1,400 miles (2,240 km) across and nearly 8 miles (13 km) deep - at the lunar poles. Due to the very slight "tilt" of the Moon's axis, only 1.5°, some of these deep craters never receive any light from the Sun - they are permanently shadowed. It is in such craters that scientists expect to find frozen water if it is there at all. If found, water ice could be mined and then split into hydrogen and oxygen by solar panel-equipped electric power stations or a nuclear generator. Such components could make space operations as well as human colonization on the Moon possible. Although the equatorial Moon rock collected by Apollo astronauts contained no traces of water, the recent Clementine mission suggested that small, frozen pockets of water ice (remnants of water-rich comet impacts) may be embedded unmelted in the permanently shadowed regions of the lunar crust. Although the pockets are thought to be small, the overall amount of water was suggested to be quite significant - one billion cubic meters, or an amount the size of Lake Erie. The presence of useable quantities of water on the Moon would be an important factor in rendering lunar habitation cost-effective, since transporting water (or hydrogen and oxygen) from Earth would be prohibitively expensive.
Compared to that of the Earth, the Moon has a very small magnetic field. While some of the Moon's magnetism is thought to be intrinsic (such as a strip of the lunar crust called the Rima Sirsalis), collision with other celestial bodies might have imparted some of the Moon's magnetic properties. Indeed, a long-standing question in planetary science is whether an airless solar system body, such as the Moon, can obtain magnetism from impact processes such as comets and asteroids. Magnetic measurements can also supply information about the size and electrical conductivity of the lunar core -- evidence that will help scientists better understand the Moon's origins. For instance, if the core contains more magnetic elements (such as iron) than the Earth, then the impact theory loses some credibility (although there are alternate explanations for why the lunar core might contain less iron).
Blanketed atop the Moon's crust is a dusty outer rock layer called regolith. Both the crust and regolith are unevenly distributed over the entire Moon. The crust ranges from 38 miles (60 km) on the near side to 63 miles (100 km) on the far side. The regolith varies from 10 to 16 feet (3 to 5 meters) in the maria to 33 to 66 feet (10 to 20 meters) in the highlands. Scientists think that such asymmetry of the lunar crust most likely accounts for the Moon's off-set center of mass. Crustal asymmetry may also explain differences in lunar terrain, such as the dominance of smooth rock (maria) on the near side of the Moon.
The Moon has a relatively insignificant and tenuous atmosphere. One source of this atmosphere is outgassing - the release of gases, for instance radon, which originate deep within the Moon's interior. Another important source of gasses is the solar wind, which is briefly captured by the Moon's gravity.
La Lune dans la mythologie
The Moon has figured prominently in various mythologies and folk beliefs. The Greek goddess Artemis and the Roman Diana were associated with the Moon, as were many other female gods (but notice that the Japanese goddess Amateratsu is associated with the Sun and her brother, Susanowo, with the Moon, an unusual inversion that Tolkien's invented Middle Earth mythology repeats, making Isil, the Moon, male, while Anar, the Sun, is female).
The term lunacy is derived from Luna because of the folk belief in the Moon as a cause of periodic insanity. Folklore also stated that lycanthropes such as werewolves and weretigers, mythical creatures capable of changing form between human and beast, drew their power from the Moon and would change into their bestial form during the full Moon.
In Roman mythology, Luna was the goddess of the moon. See Selene for more details.
L'exploration lunaire
La face éloignée de la Lune, incorrectement appelée la "face sombre", a été vue pour la première fois le 15 septembre 1959 lorsque la sonde automatique Luna 2, lancée par l'Union Soviétique, s'est mise en orbite autour de la Lune. "The dark side" is a misnomer since it is lit up by the Sun in the same way as the near side, it is just that we never see it from our vantage point on Earth.
Le premier alunissage des humains eu lieu le 20 juillet 1969. Ce fut le point culminant de la course spatiale engagée entre les USA et l'URSS, alors en pleine guerre froide.Le premier astronaute à poser le pied sur la Lune fut Neil Armstrong, le capitaine de la mission Apollo 11. Le dernier homme à marcher sur le sol lunaire était le scientifique Harrison Schmitt, lors de la mission Apollo 17 en décembre 1972.
L'astronaute Harrison Schmitt se tenant debout à coté du rocher Taurus-Littrow durant la troisième sortie extra-véhiculaire de la mission Apollo 17. cliquez pour aggrandir l'image
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