THE MOON

Data from Wikipedia and NASA (C)

The Moon is the only natural satellite of the Earth.

Motion of the Moon

The face of the Moon turned in opposite direction to the Earth comes called dark face, whose meant here it is meant like disowned and hidden; one refers also to black out of the radio communications, that it happens when a spaces probe them moves behind the far face. The greater part of the far face cannot be seen from the Earth, because the revolution of the moon around the earth and the rotation around its axis has the same period. A small portion can be seen thanks to the libration, that it renders irregular the motion of rotation of the Moon. In the complex from the earth it is visible approximately 59% of the lunar surface. The near face of the Moon is covered approximately by 30 000 craters (counting those with a diameter at least 1 kilometer). The largest lunar crater, and in effects largest known in the entire Solar System, of it occupies the entire South Pole. This crater is found on the far face, it has a diameter of 2240 kilometers, and is deep 13 kilometers.

The Moon and the celestial sphere

The Moon completes a complete orbit of the celestial sphere approximately every 27 days and 7 hours, but the observer on the earth counts approximately 29,5 days between a new moon and the successive one, because of the contemporary movement of Earth revolution. In the course of an hour distance it moves in the sky approximately of 0.5 degree, its angular dimension. The Moon always remains in a region of the sky called zodiac, than it extends approximately 8 degrees over and under the ecliptic.

Origins

The origins of the Moon are in the center of a scientific debate. The most credited theory is that it has formed because of the collision of an asteroid with dimensions similar to those of Mars with the Earth when this last one was still warm, in the first phase of its formation (such asteroid is called Theia). The material gushed from the impact remained in orbit around to the Earth and for effect of the gravitational force it gathered forming the Moon. It is the Theory of the Giant Impact. A confirmation of this thesis derives from the fact that the composition of the Moon is almost identical to that one of the Earth’s cape without the lighter elements, evaporates for the lack of an atmosphere and the gravitational force necessary in order to withhold them. Moreover, the inclination of the orbit of the Moon rather renders the theories improbable if the Moon was formed with to the Earth or was captured later on.

Caratteristics

Since the period of rotation of the Moon is exactly equal to its orbital period, we sees always the same face of the Moon, revolt towards the Earth. This synchrony is the result of the gravitational clutch that has slowed down the rotation of the Moon in its history. Because of these forces, said also tide forces, also the rotation of the Earth comes gradually slowed down, and the Moon goes away slowly from the Earth while the rotational moment of this last one comes transferred at the orbital moment of the Moon. The gravitational attraction that the Moon exercises on the Earth is the cause of the tides of the sea. The variations of the tide are synchronized with the orbit of the Moon around the Earth. The Earth and the Moon orbit round to a common center of mass, that distance of approximately 4700 kilometers from the center of the Earth is found to one. Since this center is found within to the Earth mass, the motion of the Earth better is described like an oscillation. Sights from the North Pole of the Earth, the rotations of the two celestial bodies, the orbit of the Moon around the Earth and the orbit of this around the Sun are all in counter-clockwise sense. Regarding the other satellites of the solar system, the Moon is exceptionally large regarding the planet around which orbit, a lot that the Earth-Moon system can be considered a double planet ("nearly" because the center of gravity of the Earth-Moon system is however a little inside of the Earth). Generally, satellites of comparable dimensions to the Moon orbit around the gaseous giants (Jupiter, Saturn), while the analogous planets to the Earth do not have satellites (Venus) or they have some small (Mars). The plan of the orbit of the Moon is tilted of 5 degrees regarding that one of the orbit of the Earth around to the Sun (the plan of the ecliptic). The orbital plan of the Moon, together to its rotation axis, rotates in hour sense with a period of 18,6 years, always maintaining an inclination of 5 degrees; this movement is correlated to the Earth nutations, that they possess in fact the same period. The points where the lunar orbit intersects the ecliptic are call the "lunar nodes". The solar eclipses happen when a node coincides with a new moon; the lunar eclipses when a node coincides with a full moon. The geological eras of the Moon they come defined based on the dating of some craters that have had a meaningful effect on its history. The tide forces that today cause the earth tides was active also when the Moon was in formation, and still fused. Then it was cooled off and it was made solid, but it maintained the shape of a ellissoid with the greater axis toward the Earth.

Chemical composition

More than 4,5 billions than years ago, the surface of the Moon was a liquid magma ocean. The scientists think that one of the components of lunar cliffs (said KREEP, acronym of the English expression K (potassio), Rare Earth Elements (rare-earths), and P (phosphorus), represent the last rest of the original magma. The KREEP is composed from that that the scientists call "incompatible elements": they are elements that cannot enter to make part of the structures of crystals, and that therefore they are leaves unusable on the surface of the magma. For the investigators, the KREEP is a useful marker, in order to determine the history of the lunar volcanism and to trace the chronology of the impacts from celestial comet and other objects. The lunar crust is composed from a variety of primary elements: uranio, thorium, potassio, oxygen, silicon, magnesium, iron, titanium, soccer, aluminum and hydrogen. When it comes bombed from the cosmic beams, every element reemits in the space a its own particular radiation, under shape of gamma beams. Some elements, like uranium, thorium and potassium, are radioactive and emit gamma beams. Which is their cause, the range beams emitted from every element are various, and a spectrometer can distinguish them, and exactly in this way it has been possible to discover of the existence. A total map of the Moon of abundance of these elements, still has not been realized. The Moon for great part of its ancient history has been bombed from comets and asteroids, many rich of water. The energy of the solar light divides the greater part of this water in its constituent elements, hydrogen and oxygen, of which the greater part it is dispersed immediately in the space. It has been but assumed that meaningful amount of water can remain on the Moon, on the surface, or inglobate in the crust. The datas of the probe Clementine suggested that in the zones permanently in shadow of the crust can be found small iced zones, than do not have occasion to melt itself. Even if these zones are probably small, the water amount total could be remarkable: a billion of cubic meters, as the volume of the lake Erie. Some water molecules, moreover, could directly be landed to the surface and be remained caught within craters of the lunar poles. Because of the modest inclination of the lunar rotation axis (only 1,5°), some of deepest polar craters never do not receive light from the Sun, always remaining in shadow. It is in these craters that the scientists expect to find water, if present. If it were found, the water (under ice shape) can be extracted and therefore divided in hydrogen and oxygen from generators to solar energy. The presence of usable water on the Moon could be an important factor in possible rendering its colonization, because the transport from the Earth would be extremely expensive. The cliffs of the Moon collected from the astronauts, all coming from from the equatorial zone, did not introduce some water trace. Not even the more recent probe Lunar Prospector, or other searches, has found some evidence of water, ice or vapor of water.

Magnetic field

The magnetic field of the Moon is much low to comparison of that earthling. It is believed that a part of it is intrinsic (as in a part of the lunar crust called Sirsalis Rhyme), while the collisions with other celestial bodies can have some formed an other part. In effects, one of the issues still opened in planetary science is if a body without air, like the Moon, can obtain a magnetic field from impacts with comets and asteroids. The measurements of the magnetic field can give to moreover information on the dimension and the electrical conductivity of the lunar nucleus, supplying therefore datas for a better theory of the origin of the Moon. As an example, if the nucleus contained a greater proportion of magnetic elements (like the iron) regarding that earthling, the theory of the birth for impact would lose credit (even if could exist explanations alternatives for this fact). Over all the lunar crust spreads a external powder cliff layer, call regolite. The crust and the regolite are distributed in irregular way, one with one thickness from 60 to 100 kilometers, the other passing from 3-5 meters in the seas until 10-20 meters on the heights. The scientists think that these asymmetries are sufficient in order to explain the movement of the center of mass of the Moon. The asymmetry of the crust could also explain the difference in lunar lands, that they are formed mainly from seas on the near face, and cliffs on the far part.

History of the lunar exploration

The hidden face, always opposite to the Earth, of the Moon came observed for the first time on 7 October 1959, when the Soviet probe Moon 3 was put in orbit around the Moon and sended to some its photographies to the Earth. The men are land on the Moon on the 20 July 1969, to the apex of a contest space them between USSR and United states, inspired from the Cold War. The first astronaut to walk on the lunar surface was Neil Armstrong, commander of Apollo 11. The last one was Eugene Cernan, than during the mission Apollo 17 December 1972 walked on the Moon. The crew of Apollo 11 left a stainless steel plate, in order to commemorate the landing and to leave information on the every visit to other being, human or less, than he finds it. On the plate it is written: Here men from the Planet Earth first set foot upon the moon, July 1969, A.D. We came in peace for all mankind. The plate represents the two hemispheres of the planet Earth, and is signed from the three astronauts and the American President Richard Nixon. In total the Apollo missions was 6, Apollo 11, 12, 14, 15, 16 and 17, for a total of 12 astronauts on our satellite; the mission Apollo 13 did not land on the Moon because of an incident during the flight, and remaining previewed missions Apollo 18,19 and 20 was cancelled for cuts budgetary. After the landing of the Apollo Program, no human being more has walked on the Moon. The Americans lost interest, the Soviet ones continued with the landing of automatic probes (between which the Lunakhod), that they brought back also ground champions on the Earth. The other nations did not have the necessary resources, and nobody would have advantage in the exploration to justify the highest costs.