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moon

moon
The moon, photographed with a 103 mm refractor.
Central bodyearth
Properties of the orbit[1]
Major semi-axis384 400 km
Periapsis363 300 km
Apoapsis405 500 km
eccentricity0,0549
Orbit inclination5,145°
Orbital time27.3217 days
Mean orbital velocity1.023 km / s
Physical Properties [1]
Albedo0,12
Apparent brightness−12.74 mag
Average diameter3476 km
Dimensions7,349 · 1022 kg
surface37,932,330 km²
Medium density3.341 g / cm³
Sidereal rotation27,322 days
Axis inclination6,68°
Gravitational acceleration on the surface1.62 m / s²
Escape speed2380 m / s
Size comparison between
Earth (⌀ = 12,756 km) and
Moon (⌀ = 3476 km)
(Photo montage with true-to-scale sizes; however, the mean distance is 30 earth diameters)

The moon (LatinLuna) is the only natural satellite on earth. Since the discovery of satellites on other planets of the solar system, in the figurative sense mostly referred to as moons, it has also been used to avoid confusion Earth moon called. With a diameter of 3,476 km, it is the fifth largest moon in the solar system.

Due to its relative proximity, it is the only alien celestial body that has so far been entered by humans and thus also the most widely explored. Nevertheless, there are still a lot of ambiguities, for example with regard to its origins and some types of terrain. However, the more recent evolution of the moon has largely been clarified.

Its astronomical symbol☾ is the waning crescent moon viewed from the terrestrial northern hemisphere.

Orbit and rotation

Apparent movement

The moon orbits the earth for an average of 27 days, 7 hours and 43.7 minutes in relation to the fixed stars from west to east in the same direction of rotation with which the earth rotates on its own axis. From the point of view of an earthly observer, it orbits the earth in one day due to the relative movement of its much faster rotation - as do the fixed stars and planets similar to the sun. In relation to the earth's surface, it therefore runs in the opposite direction as in relation to the fixed stars and its rise, like that of these other celestial bodies, takes place in the east, its setting in the west. Since the moon's orbital movement has the same right-hand direction of rotation as the earth's rotation, its apparent earth orbit lasts 50 minutes longer than 24 hours. This difference adds up to a day over the course of a month, as the moon makes a true orbit around the earth during this time.

The apparent orbits of the moon and sun have a similar course, since the lunar orbit is only slightly inclined towards the ecliptic. For an observer in the northern hemisphere about 5.2 ° north of the tropic of the tropics, the moon and sun are at their highest orbital points (culmination) in the south, for an observer in the southern hemisphere over 5.2 ° south of the tropic in the north. The surface structures appear inverted compared to the northern hemisphere. Depending on the distance, the apparent diameter of the moon fluctuates between almost 30 'and a good 34' around a mean value of around 32 'arc minutes and is thus approximately the same as that of the sun.

Orbit

The orbit of the moon around the earth deviates significantly from the circular shape. The greatest and the smallest distance to the earth deviate from the circular shape by an average of 5.45% each. As a good approximation, the path is an ellipse with a numerical eccentricity of 0.0549. The mean distance of the center of gravity of the moon from the center of the bary - the semi-major axis - measures 384,400 km. The closest point to the earth is called perigee. In perigee the average distance is 363,300 km. The most distant point is called apogee. The average distance there is 405,500 km. The passages of the moon through the orbital plane of the earth (the ecliptic) are called Lunar knot (or dragon points). The ascending node is the transition to the north side of the ecliptic, the descending node marks the transition to the south side.

Correct size-distance relationship between earth and moon

The moon orbits the sun together with the earth, but due to the movement around the earth the moon oscillates around a common elliptical orbit. The variation of the gravitation during this pendulum movement leads together with smaller disturbances from the other planets to deviations from an exact Keplerellipse around the earth.

The closest point of the orbit is not reached again after exactly one orbit (relative to the fixed stars) of the moon. This rotation of the apse causes the perigee to orbit the earth in 8.85 years. Even two ascending node passes do not take place exactly after one cycle, but after a shorter time. The lunar nodes consequently revolve around the earth retrograde, that is, against the direction of rotation of the moon in 18.61 years. If a nodal passage coincides with a new moon, a solar eclipse occurs, and if the nodal passage coincides with a full moon, a lunar eclipse occurs.

This cycle also leads to the turning of the moon: The place of the moon's rise on the horizon fluctuates between a southernmost and a northernmost point during a month, as is the case with the sun over the course of a year. In the course of the period of 18.61 years, the distance between these two extreme points changes: The point in time (most recently in 2006) at which these points are the furthest apart is called great lunar change, that of the closest distance little lunar turn. These lunar turns played an important role in early astronomy [2].

Orbit period

The duration of one orbit of the moon month (to moon), can be determined according to various criteria, each of which covers different aspects.

  • After a sidereal In the 3rd month (27.32 d) the moon again takes the same position to the fixed stars (observed from the earth).
  • After a synodic In the month (29.53 d; period of the phases of the moon - one lunar day) the moon reaches the same position to the sun again (observed from the earth).
  • One draconian He needs month (27.21 d) to run through the same node of his orbit again; it is important for the solar and lunar eclipses.
  • One anomalistic Month (27.56 d) the moon needs from one perigee passage to the next.

However, these values ​​increase very slowly over the course of millions of years, as the lunar orbit increases (see section: Enlarging the orbit).

Phases of the moon

The appearance of the moon varies in the course of its orbit and goes through the phases of the moon:

Moon phases from new moon to full moon to shortly before the next new moon
  • New moon (1) - the moon stands between the sun and the earth,
  • waxing moon (2–4) - visible in the evening,
  • Full moon (5) - the earth stands between the sun and the moon,
  • waning moon (6–8) - visible in the morning,
  • Half moon - increasing (3) or decreasing (7) - is the half phase (dichotomy).

This representation applies to the observation from the northern hemisphere (the earth). If the moon is viewed from the southern hemisphere instead, the visual appearance is reversed: new moon (1), shortly after (9), waxing moon (8, 7, 6), full moon (5), waning moon (4, 3 , 2). To an observer near the equator, the crescent moon appears horizontal and the direction of the phase change perpendicular to the horizon. This dependence of the location on the latitude is reflected, for example, in the use of a symbolic crescent moon in the form of a bowl on the national flag of some equatorial countries (example: flag of Mauritania).

The parts of the moon side facing the earth that are not illuminated by the sun are never completely dark, because they are illuminated by the light reflected from the sun-lit earth, which is called earth light or earth light. Its reflection through the reflection from places on the lunar surface is also Ash gray moonlight called. It is best seen when the crescent moon is narrow.

Away from sunlight through earth light to ash gray moonlight

Its cause was already correctly recognized by Leonardo da Vinci. With binoculars, even with low magnification, details can even be seen on the moon surfaces illuminated by the earth, because due to the larger diameter and higher reflectivity (albedo) of the earth, the "full earth" is around 50 times as bright as the full moon. Measurements of the ash-gray moonlight allow conclusions to be drawn about changes in the earth's atmosphere. When the moon is full, its illuminance is 0.2 lux.

The back of the moon, which is constantly facing away from the earth, is of course not always dark, but is subject to the correspondingly shifted phase change - at a new moon it is completely illuminated by sunlight.

Eclipses

Eclipses between the sun, moon and earth occur when the three celestial bodies are on one line, that is, only with a full moon or new moon and when the moon is in one of the two lunar nodes. This only happens twice a year.

lunar eclipse
Total lunar eclipse on November 9, 2003

During a lunar eclipse, which can only occur with a full moon, the earth stands between the sun and the moon. It can be observed on the entire night side of the earth and lasts a maximum of 3 hours 40 minutes. One distinguishes

  • the total Lunar eclipse in which the moon moves completely into the shadow of the earth. The totality lasts a maximum of 100 minutes. If you consider the geometric relationships in a total lunar eclipse, the moon should lie in the umbra of the earth, which theoretically should extend almost 1.4 million kilometers into space, but actually only extends about 250,000 km due to the strong scattering by the earth's atmosphere . The moon is therefore not completely darkened even in total eclipses. Since the earth's atmosphere scatters the blue parts of the sunlight more than the red, the moon appears as a dark red-brown disc in total eclipses; hence the occasional term "blood moon".
  • the partial Lunar eclipse in which only part of the moon is shaded by the earth, that is, part of the moon remains visible during the entire course of the eclipse.
  • the Penumbral eclipsein which the moon only (completely or partially) dips into the penumbra of the earth. Penumbral eclipses are fairly inconspicuous; there is only a slight graying of the moon side that is closest to the umbra of the earth.

Seen from the moon, a lunar eclipse is a solar eclipse. The sun disappears behind the black disc of the earth. With a total lunar eclipse, there is total solar eclipse on the entire front of the moon, with a partial lunar eclipse, the solar eclipse on the moon is only total in some areas, and with a penumbral lunar eclipse there is partial solar eclipse on the moon. There are no annular solar eclipses on the moon because of the much larger apparent diameter of the earth's disk in relation to the sun; only through the described light scattering in the earth's atmosphere the edge of the black disk becomes a copper-red shimmering ring, which gives the moon the corresponding color.

Solar eclipse

In a solar eclipse, which can only occur at a new moon, the moon stands between the sun and earth. It can only be observed in the areas that pass through the umbra or penumbra of the moon; these areas usually appear as long, but very narrow strips on the surface of the earth. A distinction is made between:

  • total Solar eclipse in which the moon completely covers the solar disk for a few minutes and the earth covers the umbra (umbra) the moon passes through;
  • partial Solar eclipse in which the moon does not completely cover the solar disk; the observer is in the penumbra (Penumbra) of the moon;
  • annular Solar eclipse, when the moon does not completely cover the solar disk because the distance from the earth is too great (see also: Passage).

A Solar eclipse is only perceived as such by the earthly observer. The sun continues to shine, of course, while the earth is in the shadow of the moon. Corresponding to the lunar eclipse, one would correctly have to speak of one Earth eclipse speak.

Saros period

It was already known to the Chaldeans (around 1000 BC) that eclipses occurred after a period of 18 years and 11 days, the Saros period, to repeat. After 223 synodic or 242 draconian months (from lat.draco, Dragon, old astrological symbol for the lunar knot, since a moon- and sun-eating dragon was assumed there) there is almost the same position of sun, earth and moon to each other, so that an eclipse position results again after 18 years and 11.33 days. The reason for this period lies in the fact that during an eclipse, both the sun and the moon must be close to the nodes of the lunar orbit, which circle the earth once every 18 years. Thales used this period, which he got to know on a trip to the Orient, for his eclipse forecast of May 28, 585 BC. BC, whereby a battle between Lydern and Medes was broken off and their war ended.

A Saros cycle is a series of solar or lunar eclipses, each of which follows one another at intervals of a Saros period. Since the agreement of the 223 and 242 months is not exact, a Saros cycle breaks off after about 1300 years. In this period, however, many new cycles begin and there are always around 43 concurrent nested Saros cycles.[3]

Enlargement of the orbit

The mean distance between the moon and the earth grows by about 3.8 cm annually. Since the first Apollo 11 lunar expedition, the lunar distance has been measured regularly by lidar by determining the time of flight that the laser light needs for the route there and back. For this purpose, a total of five retroreflectors were placed on the moon by both American and Soviet lunar missions, which are used today for distance measurements (see also:Lunar Laser Ranging).

root cause

The gradually increasing distance is a result of the tidal forces that the moon causes on earth. Rotational energy from the earth is largely converted into heat and part of it is transferred to the moon as rotational energy. The decreasing angular momentum of the earth's rotation results in an increase in the orbital angular momentum of the moon, which thereby moves away from the earth. This effect, which has long been suspected, has been secured by laser distance measurements since 1995. It causes both a continuous lengthening of the earthly day length (by about one second in 100,000 years) and the duration of the lunar revolution.

Type of angular momentumSize [kg · m² / s]proportion of
Earth-moon system as a whole3,49 × 1034100,0 %
Moon - intrinsic angular momentum2,33 × 1029–––
Moon - orbital angular momentum2,87 × 103482,2 %
Earth - intrinsic angular momentum5,85 × 103316,8 %
Earth - orbital angular momentum3,53 × 10321,0 %
Future development

Nevertheless, even in the distant future, the earth cannot completely lose the moon due to the tidal mechanism, since after a few billion years a final state would arise in which the earth's own period of rotation, i.e. H. the length of a day, which would then have adjusted to the extended lunar period. In this final state, the tidal mechanism (and the associated energy and angular momentum transmission) would have come to a standstill and the moon would from now on always stand over the same place on earth, similar to a geostationary satellite. (However, this case will not occur in the first place, as other cosmic events, such as the swelling of the sun into a red giant, will occur sooner.)

Corresponding to the angular momentum proportions of the earth-moon system (see table), the current orbital angular momentum of the moon would increase by a factor of 1.2 to the maximum possible around 99% of the total angular momentum by largely taking over the earth's own angular momentum. This resulted in a 1.22-fold enlarged mean lunar distance of about 560,000 km and a 1.23-fold extended period of around 48 days. The time it takes to reach this end state can be changed downward Roughly delimit by extrapolating the current increase in distance of 3.8 cm / year linearly. This amounts to around 5 billion years and is therefore in the same time frame as the aforementioned final stage of our sun.

rotation

As a result of the tidal action, which is caused by the earth's gravity, the moon has adjusted its rotation to the orbit time in the form of a bound rotation. This means that when it goes around the earth, it rotates exactly once around its own axis in the same direction of rotation. Therefore - apart from minor deviations, the librational movements - the same side of the moon can always be seen from one point on the earth's surface. Because of the libration and parallax, i.e. by observing different points at moonrise and moonset, a total of almost 59% of the moon's surface can be seen from the earth. With the space probe Lunik 3, the far side of the moon could be observed for the first time in 1959.

As a result of the bound rotation, a stationary observer on the moon always sees the earth at roughly the same point in the sky, apart from monthly movements around the earth-moon center of gravity and fluctuations through the orbit, the librations that together form a monthly loop of the earth 18 ° effect. The earth never "rises" or "sets" outside of the libration zones on the moon, but is always visible on the side of the moon facing the earth and never visible on the side facing away from the earth.

Because of the lack of an atmosphere, the lunar sky is not colored, but black, since no scattered light can be observed. However, stars can basically only be seen on the moon at night; the human eye adjusts itself to the brightly irradiated moon surface and can then no longer perceive the stars. After looking at the sky for a long time until the eyes have adapted to recognize stars, there is the same risk of serious eye damage when looking at the surface of the moon as with a solar eclipse on earth without protective goggles.

The earth appears as a bluish disc, in diameter almost four times the size of the moon from the earth. The phases of the earth go through in a synodic month and are opposite to the phases of the moon. At a new moon it is “full earth” and at a full moon it is “new earth”. The sun travels through the zodiac once a year when viewed from the moon, as well as from the earth. It takes a week from sunrise to the highest point of the sun, and from there another week to sunset, followed by a 14-day night (moon night). A day-night cycle on the moon therefore lasts about a month.

See also: Extra-terrestrial views of the sky

Selenology and Selenography

When the moon is full, there are hardly any craters to be seen because of the perpendicular light, but the radiation systems are very good.

Selenology, after the Greek word for moon, Σελήνη (Selene), or "geology of the moon", deals with its origin, its structure and its development as well as with the origin of the observed structures and the processes responsible for them. The task of selenography is to create maps of the moon. Selenodesia deals with the measurement of the moon and its gravitational field.

Properties and development

The moon has with 3476 km about a quarter of the diameter of the earth and has with 3.345 g / cm³ a ​​lower mean density than the earth. Due to its rather small size difference to its planet compared to other moons, the earth and moon are sometimes referred to as double planets. Its mean density, which is low compared to the earth, remained unexplained for a long time and gave rise to numerous theories about the formation of the moon.

The model for the formation of the moon, which is widely recognized today, states that around 4.5 billion years ago a celestial body the size of Mars almost grazed the proto-earth collided. A lot of matter, mainly from the earth's crust and the mantle of the impacting body, was thrown into an earth orbit, where it agglomerated and finally formed the moon. Most of the impactor merged with the proto-earth to form Earth. According to current simulations, the moon formed at a distance of around three to five earth radii, i.e. at an altitude between 20,000 and 30,000 km. Due to the collision and the released gravitational energy during the formation of the moon, it was melted and completely covered by an ocean of magma. In the course of the cooling, a crust formed from the lighter minerals that can still be found in the highlands today.

The early lunar crust was repeatedly penetrated by major impacts, so that new lava could flow from the mantle into the resulting craters. They formed Maria (Lunar seas) that only cooled down completely a few hundred million years later. The so-called last major bombardment only ended 3.8 to 3.2 billion years ago, after the number of asteroid impacts had decreased significantly about 3.9 billion years ago. After that, no strong volcanic activity is detectable, but some astronomers - especially the Russian lunar explorer Nikolai Kosyrew in 1958/59 - were able to observe isolated luminous phenomena, so-called lunar transient phenomena.

In November 2005, an international team of researchers from ETH Zurich and the Universities of Münster, Cologne and Oxford was able to precisely date the hour of birth for the first time. To do this, the scientists used an analysis of the isotope tungsten-182 and calculated the age of the moon to be 4527 ± 10 million years. Thus it was created 30 to 50 million years after the formation of the solar system [4].

shape

The mean equatorial diameter of the moon is 3,476.2 km and the pole diameter is 3,472.0 km. Its overall mean diameter - as a sphere of equal volume - is 3474.2 km[1].

The shape of the moon is more like that of a three-axis ellipsoid than that of a sphere. At the poles it is somewhat flattened with a diameter of 3472.0 km and the equatorial axis pointing in the direction of the earth is slightly larger than the equatorial axis that is perpendicular to it. The equatorial bulge is significantly larger on the side facing away from the earth than on the side close to the earth.

Towards the earth, the diameter is greatest due to the tidal force. Here, the far-earth moon radius on this axis is larger than the near-earth one. This is surprising and there is still no conclusive explanation for it. As early as 1799, Pierre-Simon Laplace reported his assumption that the equatorial bulge is more pronounced on the side facing away from the earth and influences the movement of the moon, and that this shape cannot simply be a result of the moon turning around its own axis of rotation. Since then, mathematicians and astronomers have been puzzling over the formation process from which the satellite preserved this bulge after its magma had solidified.

internal structure

Model of the shell structure of the moon consisting of the core, inner mantle, outer mantle and crust
Schematic structure of the moon (left: front, right: back)

The knowledge about the structure of the moon is essentially based on the data of the four seismometers left behind by the Apollo missions, which recorded various moon quakes and tremors caused by impacts by meteoroids, as well as on the mapping of the surface, the gravitational field and the mineral composition by the clementines - and the Lunar Prospector Mission.

The moon has a 70 (on the lunar front side) to 150 km (back side) thick crust made of anorthosite, which is covered by a several meters thick regolith layer. Underneath is a solid coat of basalt rocks (cumulates rich in olivine and pyroxene). In between there is a thin layer of KREEP - a rock that has a high proportion of Kalium, R.are E.arth E.lements (Eng. rare earths) and PContains phosphorus - which absorbed the elements that were incompatible during the crystallization of the other two rocks or that were the last to crystallize out. This was carried to the surface of the moon with large meteorite impacts and is found mainly on the front of the moon (e.g. in Oceanus Procellarum and Mare Imbrium).[5] There are indications of a discontinuity at a depth of 500 km where there could be a change in the rock composition. The ferrous core, which is at least 400 km in size, is likely to have temperatures of 1,000 to 1,600 degrees Celsius.[6]

The bound rotation of the moon also influences the shape and internal structure. The moon is elongated towards the earth and its center of mass is about 2 km closer to the earth than its geometric center.

Moonquake

Apollo 11 passive seismic experiment (PSE)

The seismometers left behind from the Apollo missions register around 3000 moonquakes per year. These quakes are very weak compared to earthquakes. The strongest achieved a strength of almost 5 on the Richter scale. Most of them are at a strength of 2. The seismic waves of the earthquakes can be followed for one to four hours. They are only very weakly attenuated in the interior of the moon.

More than half of the quakes occur at a depth of 800 to 1000 km, where the rock has partially melted (asthenosphere), and have frequency peaks during the apogee and perigee passage, that is, every 14 days. Quakes from the near-surface region of the moon are also known. The reason is that the structure of the moon has adapted to the mean value of the gravitation caused by the earth. The quakes reduce the internal tensions through tidal forces, which reach their maximum at the point of the lunar orbit furthest from and closest to the earth. The origin of the quake is not evenly distributed over a complete shell. Most quakes occur in only about 100 places, each only a few kilometers in size. The reason for this concentration is not yet known.

Seismically, the lunar crust (mean rock density 2.9 g / cm³) can be demarcated from the mantle at an average depth of 60 km. On the back of the moon, it should be about twice as thick, which would explain why the center of mass of the moon is eccentric, namely about 2 km away from the geometric center.

Mass concentrations

The mascons of the near-earth (left) and far-earth side of the moon

Due to unusual influences on the orbits of the lunar orbiter missions, the first indications of gravity anomalies were received at the end of the 1960s, which mascons (Mass concentrations, Mass concentrations). These anomalies were examined more closely by Lunar Prospector; they are mostly located in the center of the craters and are probably caused by the impacts. Possibly it is the iron-rich cores of the impactors, which could no longer sink to the core due to the progressive cooling of the moon. Another theory could be lava bubbles that rose from the mantle as a result of an impact.

surface

The topography of the near-earth (left) and far-earth sides of the moon

The surface of the moon is 38 million km2 about 15% larger than the area of ​​Africa with the Arabian Peninsula. It is almost completely covered by a dry, ash-gray layer of dust, the regolith. The apparent "silver sheen" is only faked to an earthly observer by the contrast to the night sky, in reality the moon even has a particularly low albedo (reflective ability).

The lunar surface shows chain mountains, trenches and grooves, flat domes and large plains of solidified magma, but no active tectonics like the earth. The maximum difference in level between the deepest depression and the highest peak is 16 km - compared to around 20 km of the surface of the earth's crust.

Chemical composition of the lunar crust

The composition of the lunar crust is similar to that of terrestrial basalt. It consists of aluminum silicates and calcium, iron, magnesium and other metal oxides as well as non-metals and gases.

elementproportion ofelementproportion ofelementproportion of
oxygen43 %titanium2 %sulfur0,1 %
Silicon21 %nickel0,6 %phosphorus0,05 %
aluminum10 %sodium0,3 %carbon0,01 %
calcium9 %chrome0,2 %nitrogen0,01 %
iron9 %potassium0,1 %hydrogen0,005 %
magnesium5 %manganese0,1 %helium0,002 %

Typical lunar rocks that have no earthly equivalent are KREEP, Lunabas and Lunarit.

Regolith

The moon has no atmosphere to speak of. Therefore, meteoroids of all sizes constantly hit the surface without slowing down and pulverize the rocks. Except for the young craters, the regolith created by this process covers the entire surface with a layer several meters thick, which hides the detailed structure of the subsurface. This top layer makes the investigation of the history of the moon considerably more difficult.

The regolith is mainly created from the normal material of the surface. But it also contains additions that were transported to the site by impacts. Although he is commonly called Moondust is called, the regolith is more like a layer of sand. The grain size ranges from the size of dust grains directly on the surface to grains of sand a little deeper to stones and rocks that were added later and have not yet been completely ground. Another important component are glassy solidification products from impacts. On the one hand there are small glass spheres that are reminiscent of chondrules, and on the other hand agglutinites, which are regolith grains baked by glass. In some places, almost half of the regolith consists of these agglutinites; they arise when the melted impact products solidify only after they hit the regolith layer.

New iron-silicon mineral phases were identified in the lunar meteorite Dhofar 280, which was found in Oman in 2001. One of these mineral phases (Fe2Si), which was thus clearly demonstrated in nature for the first time, was named after the researcher Bruce Hapke as Hapkeit. Bruce Hapke had the formation of such iron compounds through space erosion in the 1970s. Space Weathering) predicted. Space erosion also changes the reflective properties of the material and thus affects the albedo of the lunar surface.

The moon has no magnetic field worth mentioning, which means that the particles of the solar wind - especially hydrogen, helium, neon, carbon and nitrogen - hit the moon's surface almost unhindered and are implanted in the regolith. This is similar to ion implantation used in the manufacture of integrated circuits. In this way, the lunar regolith forms an archive of the solar wind, comparable to the ice in Greenland for the earth's climate. In addition, cosmic radiation penetrates up to about one meter deep into the moon's surface and forms unstable nuclides there through nuclear reactions (mainly spallation reactions). These transform into stable nuclides with different half-lives, including through alpha decay. Since a helium atomic nucleus is formed during each alpha decay, rocks of the lunar regolith contain significantly more helium than surface rocks on earth.

Since the lunar regolith is turned over by impacts, the individual components usually have a complex history of irradiation behind them. However, one can use radiometric dating methods for lunar samples to find out when they were near the surface. This enables knowledge to be gained about cosmic rays and the solar wind at these times.

Oxygen can be split off electrolytically from regolith. To generate one gram of oxygen, 5-20 grams of regolith and 100-200 kJ of thermal energy are required. A solar furnace with an output of 5 kW could produce one ton of oxygen per year.[7]

Maria

The Earth-facing side of the moon is shaped by most and largest of the dark low plains, which take up a total of 16.9% of the lunar surface. On the front they take up 31.2%, on the back only 2.6%. The conspicuous grouping on the near-earth side is mostly in the northern half and forms the popularly so-called "moon face". In the early days of lunar exploration, the dark surfaces were thought to be seas; they are therefore named after Giovanni Riccioli Maria (Singular: Mare) designated.

The Maria are solidified ceilings of lava inside circular basins and irregular depressions. The depressions were probably caused by large impacts in the early phase of the moon. Since the moon's mantle was still liquid at this stage of development, its floors were then flooded by rising magma. The lower crust thickness on the side of the moon facing the earth has greatly favored the magma outflows compared to those on the back. The dark mare rocks are also referred to as Lunabas without obligation.

The age of the dark basalts is 3.1 to 3.8 billion years. The plains have only a few craters and with the exception of these they show only very small differences in height of a maximum of 100 meters. These surveys include the Dorsa; the flat arching backs stretch over several dozen kilometers. The maria are covered by a 2 to 8 meter thick regolith layer rich in iron and magnesium. (See also: List of Mary of the Earth Moon)

Terrae

The highlands were previously viewed as continents and are therefore called Terrae designated. They have significantly more craters than the Maria and are covered by a regolith layer up to 15 meters thick, which is rich in light aluminum-rich anorthosite. They are selenologically older than the Maria, the rocks examined were dated from 3.8 to around 4.5 billion years and are probably the remains of the original lunar crust. From the samarium-neodymium isotope systematics of several lunar anorthosites, a crystallization age of 4.456 ± 0.04 billion years could be determined for these rocks, which is interpreted as the formation age of the first crust and the beginning of the crystallization of the original magma ocean. The highland rocks, which are lighter than the Lunabas, are called lunarite without obligation.

The highlands are criss-crossed by so-called valleys (Vallis). These are narrow depressions up to a few hundred kilometers long within the highlands. They are often a few kilometers wide and a few hundred meters deep. Most of the lunar valleys are named after nearby craters. (See also: List of the valleys of the Earth's moon)

In the highlands there are several mountains that reach heights of about 10 km. They may have been caused by the fact that the moon has shrunk as a result of the cooling, and as a result, fold mountains bulged. According to another explanation, it could be the remains of crater walls. They have been named after earthly mountains, for example the Alps, Apennines, Caucasus and Carpathians. (See also: List of the Mountains and Mountains of the Earth's Moon)

crater

The lunar craters were largely formed by asteroid impacts (impact craters) about 3 to 4.5 billion years ago in the early days of the moon. Following the Riccioli nomenclature, they are preferably named after astronomers, philosophers and other scholars. Their sizes range from 2240 km in diameter, as in the case of the South Pole Aitken Basin, to microcraters that only become visible under the microscope. With terrestrial telescopes, one can distinguish more than 40,000 craters with sizes of more than 100 meters on the front alone, but there are many times more on the back. (See also:List of craters of the moon)

Volcanic craters are likely to be very rare, but isolated escapes of gas are recorded.

Grooves

There are also groove structures (rima) on the lunar surface, the origin of which was long speculated about before the Apollo program. One distinguishes

Since the investigations of the Hadley groove by Apollo 15, it has been assumed that the meandering grooves are lava channels that were partially "roofed over". However, the ceilings collapsed in the course of the moon's development and were ground to regolith. The history of the formation of the other groove shapes is much less certain, but they could have emerged as cracks in the cooling lava.

In addition to the structures known as rima, there are also narrow, recessed structures that reach a length of over 400 km. They resemble the elongated grooves (rimae) and are known as furrows or cracks (rupes). These furrows are considered evidence of the action of tension forces within the lunar crust.

Away from the earth

Nothing was known about the back of the moon before the first space missions, as it is not visible from Earth, only Lunik 3 provided the first images. It differs from the front in several respects. Its surface is shaped almost exclusively by highlands rich in craters; this also includes the large South Pole Aitken Basin, a 13 km deep crater with a diameter of 2240 km, which is overdrawn by many other craters. Investigations by the Clementine mission and the Lunar Prospector suggest that a very large impact body pierced the lunar crust and possibly exposed mantle rocks. The crust on the back is about twice as thick with 150 km compared to 70 km on the front.

The old saying about the "dark side of the moon" dark side of the moon) for the moon side facing away from the earth is to be understood only symbolically in the sense of an unknown side; In the actual sense of the word, the phrase is wrong, because - as already noted about the moon phases - the front and back are alternately illuminated by the sun in the course of the moon's rotation. Due to the much smaller area of ​​the dark mare plains, the far-earth side of the moon is overall significantly brighter than the near-earth side.

water

The moon is an extremely dry body. In the samples brought to earth by the astronauts of the Apollo missions, traces of water could only be reliably detected in 2010.

However, with the help of a new method in the summer of 2008, scientists were able to detect tiny traces of water (up to 0.0046%) in small glass spheres of volcanic origin in Apollo samples. This discovery suggests that the massive collision that created the moon did not evaporate all of the water.[8]

In addition, the Lunar Prospector probe found evidence of water ice in the craters of the polar regions of the moon; this water could come from comet crashes. Since the polar craters are never directly irradiated by the sun due to the slight inclination of the lunar axis towards the ecliptic and thus the water cannot evaporate there, it could be that there is still water ice bound in the regolith. The attempt to obtain clear evidence by deliberately crashing the Prospector into one of these polar craters failed, however.

In September 2009, the Indian probe Chandrayaan-1 discovered evidence of large amounts of water on the moon.[9]

On November 13, 2009, NASA confirmed that the data from the LCROSS mission suggest that there is a large amount of water on the moon.[10]

In March 2010, the United States Geological Survey announced that re-examinations of the Apollo samples using the new method of secondary ion mass spectrometry found up to 6000 ppm (0.6%) water. The water has a hydrogen isotope ratio, which deviates significantly from the values ​​of terrestrial water.[11]

In October 2010 a further analysis of the LCROSS and LRO data showed that there is much more water on the moon than previously assumed. Hydroxyl ions, carbon monoxide, carbon dioxide, ammonia, free sodium and traces of silver were also detected.[12][13]

the atmosphere

The moon has no atmosphere in the strict sense of the word, just an exosphere. It consists of roughly equal parts helium, neon, hydrogen and argon and has its origin in particles trapped in the solar wind. A very small part also arises from outgassing from the interior of the moon, whereby in particular 40Argon produced by the decay of 40Potassium originates in the interior of the moon, is important. Interestingly, it becomes part of this 40Argon, however, is driven back to the surface of the moon by the magnetic field carried along by the solar wind and taken over into the topmost layer of dust particles. There 40Potassium used to be more common and therefore more 40Argon gas can be determined by measuring the 40Argon/36Argon ratio of lunar material can be determined at what time it was in the top layer of the lunar regolith. There is a balance between the trapped atoms and the loss due to temperature-related escape.

Surface temperature

Due to the slow rotation of the moon and its extremely thin gas envelope, there are very large temperature differences on the moon's surface between the day and night sides. During the day the temperature reaches a height of up to about 130 ° C and at night it drops to about −160 ° C. The average temperature is 218 K = −55 ° C. In some areas there are local anomalies in the form of a slightly higher or slightly lower temperature in neighboring areas. Craters that are considered relatively young in age, such as Tycho, are slightly warmer than their surroundings after sunset. Probably they can better store the solar energy absorbed during the day through a thinner layer of dust. Other positive temperature anomalies may be due to slightly increased local radioactivity.

Dimensions

The lunar mass can be determined using Newton's law of gravity by examining the path of a body in the moon's gravitational field. A good approximation for the lunar mass can be obtained if one considers the earth-moon system as a pure two-body problem.

In a first approximation, earth and moon represent a two-body system, with both partners having their common center of gravityS. circle. In the two-body system of earth and sun, this center of gravity practically coincides with the center of the sun, since the sun is much more massive than the earth. In the case of the earth and moon, however, the difference in mass is not that great, so the earth-moon center of gravity is not in the center of the earth, but rather far away from it (but still below the surface). One now denotes with r1 the distance from the center of the earth to the center of gravity S. and r2 the distance of the center of the moon from the same, it follows from the definition of the center of gravity:

,

that the mass ratio of earth M. to moon m just the ratio of r1 to r2 corresponds to. So it's all about how big r1 and r2 are - i.e. where the center of gravity of the system is.

Without the moon and its gravity, the earth would follow an elliptical orbit around the sun. In fact, however, the center of gravity of the earth system, the moon, moves on an elliptical orbit. The rotation around the common center of gravity creates a slight ripple in the earth's orbit, which causes a small shift in the position of the sun as seen from the earth. From data measured by astronomers this shift became r1 calculated to be about 4670 km, i.e. about 1,700 km below the earth's surface (the radius of the earth is 6378 km). Since the moon does not describe an exact orbit around the earth, one calculates r2 about the middlemajor semi-axis minus r1. So it applies r2 = 384,400 km - 4,670 km = 379,730 km.

This results in the mass ratio

,

with which the mass of the moon is about 1/81 of the mass of the earth. By inserting the earth mass M. ≈ 5,97 · 1024 kg results in the mass of the moon

.

More precise measurements give a value of m ≈ 7,349 · 1022 kg.

Magnetic field of the moon

The analysis of the lunar lump Troctolite 76535, which was brought to earth with the Apollo 17 mission, points to a permanent magnetic field of the earth's moon and thus to a formerly or still liquid core.[14] However, the moon no longer has a magnetic field.[15]

miscellaneous

Influences on the earth

The gravity of the moon drives the tides on earth. This includes not only the ebb and flow of the oceans, but also the upward and downward movement of the mantle. The energy released by the tides is taken from the rotation of the earth and the angular momentum contained in it is fed to the orbital angular momentum of the moon. This currently increases the length of the day by around 20 microseconds per year. In the distant future the rotation of the earth will be tied to the orbit of the moon and the earth will always turn the same side to the moon. The distance between the earth and the moon will then be about twice as large as it is today because of the transmitted angular momentum.

Due to the constant deceleration of the earth's rotation, the interior of the earth tends to rotate differently with respect to the earth's crust due to its inertia. It is assumed that the resulting forces in the earth's interior are jointly responsible for the creation of the earth's magnetic field.

The earth is not perfectly spherical, but has a larger radius at the equator than at the poles. The gravitation of the sun and the moon attacks this asymmetrical mass distribution. These tidal forces acting on the earth as a whole thus generate a torque in relation to the center of the earth. Since the earth is an otherwise freely rotating top, the torque causes a precession