# moon

moon
The moon photographed from the earth (2006)
Central body earth
Properties of the orbit
Major semi-axis 384,400 km
Periapsis 363,300 km
Apoapsis 405,500 km
eccentricity 0.0549
Orbit inclination (to the ecliptic ) 5.145 °
Orbital time 27.3217 d
Mean orbital velocity 1.022 km / s
Physical Properties
Albedo 0.12
Apparent brightness −12.74 (full moon) mag
Medium diameter 3474 km
Dimensions 7.346 x 10 22 kg
surface 37,932,330 km 2
Medium density 3.344 g / cm 3
Sidereal rotation 27,322 days
Axis inclination 6.68 °
Acceleration of gravity on the surface 1.62 m / s 2
Escape speed 2380 m / s
Surface temperature 95 K to 390 K
Size comparison between
earth (ø = 12,756 km) and
moon (ø = 3476 km)
(photo montage with true-to-scale sizes; however, the mean distance is 30 earth diameters)

The moon ( mhd. Mâne ; Latin luna ) is the only natural satellite on earth . Its name is etymologically related to month and refers to the period of its phase change . Because the satellites of other planets in the solar system are usually also referred to as moons in the figurative sense, one sometimes speaks of the earth's moon to avoid confusion . With a diameter of 3476 km, it is the fifth largest known moon in the solar system and, compared to its central body, the earth, is also extraordinarily large (about a quarter of the diameter of the earth).

Because it is relatively close to earth, it is the only alien celestial body that humans have entered and the one that has been best explored. Nevertheless, there are still a lot of ambiguities, for example with regard to its formation 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 as it appears (open to the right) from the northern hemisphere of the earth.

## etymology

The Common Germanic designation of the celestial body is in Middle High German mān [e] , in Old High German māno and goes to the Indo-European original language mēnōt- “moon; Moon change, month “back.

## Orbit

### Apparent movement

Setting of the narrow crescent of the waxing moon at dusk on Cerro Paranal ( Chile ). The two noticeable points of light that “follow” the moon are the planets Mercury and Venus .

The moon orbits the earth with respect to the fixed stars in an average of 27 days, 7 hours and 43.7 minutes. It revolves around the earth from west to east in the same direction as the earth rotates around its axis . It orbits a terrestrial observer the earth because of their much faster rotation seemingly on a day - as well as the sun , the planets and the fixed stars - and is therefore how those in the east and sets in the west. The moon itself moves relative to the fixed stars in the right direction of rotation of the earth, so that its apparent earth orbit lasts about 50 minutes longer than 24 hours. This adds up to a full day in a month , as the moon actually orbits the earth once during this time.

The apparent orbits of the moon and sun are similar, as the lunar orbit is only slightly (currently 5.2 °) inclined to the ecliptic . For an observer in the northern hemisphere, the moon is more than 5.2 ° north of the tropic (i.e. at a geographical latitude over 28.6 °) at its daily maximum ( culmination ) always in the south, for an observer in the southern hemisphere more south than −28 , 6 ° always in the north (for the sun the analogous angle is 23.4 ° - the latitude of the tropics). This ± 28.6 ° is the maximum value. This value fluctuates in an 18-year cycle between the minimum 18.3 ° and the maximum 28.6 °, because the position of the lunar orbit (with an almost constant orbit inclination of 5.2 °) rotates slowly relative to the ecliptic, which is due to the precession (Circular motion) of the lunar orbit plane is caused by the earth's flattening of 0.3%.

The apparent size of the moon from the earth's point of view fluctuates depending on the distance between 29.4 'and 33.5' around an average of almost 32 '( angular minutes ), about 0.5 °. The size of the sun's disk fluctuates between 31.5 'to 32.5' around a similar mean. With a suitable constellation, the moon can therefore completely cover the sun and a total solar eclipse can occur.

### Railway shape

The orbit of the moon around the earth is roughly circular, more precisely elliptical. In one of the two focal points of the ellipse is not the center of the earth, but the common center of gravity, the barycenter . The mean distance of the center of gravity of the moon from the center of the bary - the major semi-axis of the ellipse - measures 383,398 km, about 60 earth radii . The center of the earth is less than a radius of the earth away from the center of the earth; the barycenter lies in the earth's mantle. The distance of the barycenter from the center of the ellipse, its eccentricity , is on average 21,296 km or 5.55% of the major semi-axis. That is how much the closest point of the orbit, the perigee , is closer or the point furthest from the earth, the apogee, further away than the major semi-axis from the center of the bary.

The moon orbits the sun together with the earth, but due to the movement around the earth the moon oscillates around a common elliptical path. 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 passages of the moon through the earth's orbital plane (the ecliptic) are called lunar nodes (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. 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 therefore orbit 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 (cf. Obsigend and Nidsigend ) . 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 furthest apart is called the great lunar turn , the one with the smallest distance is called the small lunar turn . These lunar turns played an important role in early astronomy.

### Orbit period

The photo series shows the sunlit back of the moon, invisible from the earth, during a transit of the moon between earth and the satellite ( DSCOVR , July 16, 2015)

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

• After a synodic month (29.53 d; period of the phases of the moon) the moon reaches the same position to the sun again (observed from the earth). This term of the month corresponds to the popular understanding of month, as it denotes the time span from new moon to new moon (for an observer on the moon from noon to noon).
• After a sidereal month (27.32 d), the moon takes the same position to the fixed stars again (observed from the earth or from the moon).
• He needs a draconian month (27.21 d) to run through the same knot of his orbit again; it is important for the solar and lunar eclipses .
• The moon needs an anomalistic month (27.56 d) from one perigee passage to the next.

These values ​​are mean values. In particular, the lengths of individual synodic months fluctuate due to the migration of the new moon position over the orbit ellipse. The month length increases slowly, see section: Enlarging the orbit .

### Moon phases

Schematic representation of the moon phases from new moon through full moon to the next new moon, when viewed from the northern hemisphere . Note that because of the earth's orbit around the sun, the respective positions of the moon on its orbit around the earth are not identical to the two new moon phases: The green marked angle corresponds to the difference between a synodic month and a sidereal month .

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

• New moon (1 and 9): the moon runs between the sun and the earth, but mostly does not hit the sun due to its inclination,
• waxing moon (2 to 4): crescent moon (2) visible to the west in the evening sky,
• Full moon (5): the earth stands between the sun and the moon (with or without a lunar eclipse) ,
• waning moon (6 to 8): crescent moon (8) visible east in the morning sky ,
• increasing (3) and decreasing (7) crescent ( dichotomy ).

The numbers in brackets refer to the previous illustration. The new moon is outshone by the nearby sun, indicated by camera reflections. Sometimes the length of time since the last new moon is given in days and referred to as the moon age , for example the full moon is on the 15th day of the synodic month and the moon age is then 14 days (if new moon = 0).

Increasing crescent moon with ash gray moonlight

The narrow crescent-shaped light of the waxing moon becomes visible for the first time in the western evening sky shortly before set and appears to the north-facing observer as a concave-convex figure that is open to the south or curved to the left.

To a viewer in southern latitudes it also appears low in the west, but as curved to the right or open to the north, where for him the moon reaches its highest level as does the sun at noon. At observation locations near the equator, the figure in the west appears to be lying horizontally or open at the top, as the height angle of a culmination is greater here . This dependence of the apparent position of the moon figure on the latitude is reflected in the use of a symbolic crescent moon in the form of a shell ("moon boat") on the national flag of some countries near the equator (example: flag of Mauritania ).

Away from sunlight through earth light to ash-gray moonlight

The parts of the moon side facing the earth that are not directly illuminated by the sun are never completely dark, because they are illuminated by the light reflected from the sun-lit earth - called earth light or earth light . Its reflection through the reflection at places on the moon's surface is also called ash-gray moonlight . It is best to see it at dusk a few days before or after the new moon, because then there is neither much daylight nor moonlight disturbing, and the moon is almost “full earth”. Its cause was already correctly recognized by Leonardo da Vinci . With binoculars, even at low magnification, details can even be seen on the moon surfaces that are only lit by the earth, because due to the almost four times larger diameter and the higher reflectivity (albedo) of the earth, the "full earth" is around 50 times as bright as the full moon, about 10 instead of 0.2  lux . Measurements of the ash-gray moonlight allow conclusions to be drawn about changes in the earth's atmosphere .

The back of the moon, which is constantly facing away from the earth, is subject to the phase change accordingly: When the moon is new, it is completely illuminated by sunlight.

The illuminated area of ​​the moon (degree of coverage) can be specified with , where the elongation (i.e., the angle between the moon, earth and sun) is. ${\ displaystyle {\ frac {100 \; \%} {2}} (1- \ cos e)}$${\ displaystyle e}$

### Eclipses

Eclipses occur when the celestial bodies sun and moon are in line with the earth. This only occurs with a full moon or a new moon and when the moon is then near one of the two lunar nodes.

#### 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. A lunar eclipse 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 total takes about 106 minutes at most. In a total lunar eclipse, the geometry of the moon should lie in the umbra of the earth. Theoretically, the umbra should extend almost 1.4 million kilometers into space, but in fact it only extends about 250,000 km due to the strong scattering by the earth's atmosphere. Therefore, the moon is not completely darkened even in total darkness. Since the earth's atmosphere scatters the blue parts of the sunlight more strongly than the red, the moon appears as a dark red-brown disc in total darkness; 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 eclipse.
• the penumbral eclipse , in which the moon only (fully or partially) dips into the penumbra of the earth. A penumbral eclipse is pretty inconspicuous; only the moon side, which is closest to the umbra of the earth, becomes a little grayer.

A lunar eclipse is a solar eclipse as seen from the moon. The sun disappears behind the black 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. An annular solar eclipse cannot be observed on the moon because the apparent diameter of the earth is much larger compared to that of the sun. Only the edge of the black earth disk becomes a copper-red shimmering ring, which is created by the described light scattering in the earth's atmosphere and gives the moon its color on earth.

#### Solar eclipse

Total solar eclipse with visible corona

In a solar eclipse , which can only occur at a new moon , the moon stands between the sun and earth. A solar eclipse can only be observed in the areas that pass through the umbra or penumbra of the moon; these areas are mostly long but very narrow strips on the surface of the earth. One distinguishes

• the total solar eclipse, in which the moon completely covers the sun for a few minutes and the earth passes through the umbra of the moon;
• the partial solar eclipse, in which the moon does not completely cover the sun; the observer is in this case in the penumbra ( penumbra ) of the Moon;
• the ring-shaped solar eclipse, when the moon does not completely cover the sun because it is too far away from the earth (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 speak of an earth eclipse .

#### Saros period

The Saros period was already known to the Chaldeans (around 1000 BC), and eclipses repeat themselves after a period of 18 years and 11 days. After 223 synodic or 242 draconian months (from Latin  draco , dragon, old astrological symbol for the lunar knot , since a moon- and sun-eating dragon was suspected there), the sun, earth and moon are almost equal to each other again, so that a darkness follows 18 years and 11.33 days again results. The Saros period is caused by 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 the Saros period, which he had 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 sequence 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. During this period, however, the same number of new cycles begin, and there are always around 43 concurrent nested Saros cycles.

### Enlargement of the orbit

Retroreflector set up for distance
measurement ; in the background the Apollo 11 Lunar Module
Angular momentum components of the earth-moon system
Type of angular momentum Value in
kg m 2 s −1
proportion of
Total angular momentum 3.49 · 10 34 100.0%
moon Intrinsic angular momentum 2.33 · 10 29 0<0.001%
Orbital angular momentum 2.87 · 10 34 082.2%
earth Intrinsic angular momentum 5.85 · 10 33 016.8%
Orbital angular momentum 3.53 · 10 32 001.0%

The mean Earth-Moon distance increases annually by about 3.8 cm due to the tidal friction (see Lunar Laser Ranging ). Here angular momentum (mainly) of the earth's rotation is converted into orbital angular momentum (mainly of the moon, see table).

### Rotation and libration

Simulated libration of the moon

Conversely, when the moon was still fluid and much closer to the earth, the field of the earth slowed the rotation of the moon quickly to the point of bound rotation . Since then, it has turned exactly once on its own axis per revolution, always showing us the same side. A very slight pendulum movement is superimposed on the even rotation, the so-called real libration. Most of the libration , however, is only an apparent oscillation, due to the variable angular speed of the path movement. Because of the libration and parallax , i.e. by observing different points such as moonrise and moonset, a total of almost 59% of the moon's surface can be seen from the earth or the earth is at least temporarily visible from points on this area. In 1959, the Lunik 3 space probe made it possible to observe the back of the moon for the first time.

## Physical Properties

### shape

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

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, and the equator axis pointing in the direction of the earth is somewhat larger than the equator axis perpendicular to it. The equatorial bulge is significantly larger on the side facing away from the earth than on the near-earth side.

Towards the earth the diameter is greatest due to the tidal force. The far-earth moon radius on this axis is larger than the near-earth one. This is surprising and has not yet been conclusively explained. Pierre-Simon Laplace had already suspected in 1799 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's rotation around its own axis of rotation. Since then, mathematicians and astronomers have been puzzling over how the moon formed and retained this bulge after its magma had solidified.

### the atmosphere

 pressure 3 · 10 −10  Pa helium 25% neon 25% hydrogen 23% argon 20% CH 4 , NH 3 , CO 2 traces

The moon has no atmosphere in the true sense of the word - the moon sky is z. B. not blue - but 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 is also produced by outgassing from the interior of the moon, whereby 40 Ar , which is created by the decay of 40 K in the interior of the moon, is of particular importance. However, part of this 40 Ar is driven back to the surface of the moon by the solar wind and implanted there in the uppermost particles of the regolith . Since 40 K used to be more common and thus more 40 Ar was gassed out, it is possible to determine at what time it was exposed by measuring the 40 Ar / 36 Ar ratio of lunar material. There is a balance between implantation and thermal 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 side. With the sun at its zenith , the temperature rises to around 130 ° C and falls to around −160 ° C at night. The average temperature over the entire surface 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 pretty good approximation for the lunar mass can be obtained if one regards 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 orbiting their common center of gravity . 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 within the globe). If one designates with the distance of the center of the earth and with the distance of the center of the moon from the center of gravity , follows from the definition of the center of gravity ${\ displaystyle S}$${\ displaystyle r_ {1}}$${\ displaystyle r_ {2}}$${\ displaystyle S}$

${\ displaystyle {\ frac {r_ {1}} {r_ {2}}} = {\ frac {m} {M}}}$,

that the mass ratio of earth M to moon m corresponds to the ratio of to . So it's all about how big and are - i.e. where the center of gravity of the system is. ${\ displaystyle r_ {1}}$${\ displaystyle r_ {2}}$${\ displaystyle r_ {1}}$${\ displaystyle r_ {2}}$

Without the moon and its gravity, the earth would follow an elliptical orbit around the sun. In fact, the center of gravity of the earth-moon system 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 the measured size of this displacement it was calculated to be about 4670 km, i.e. about 1700 km below the earth's surface (the radius of the earth is 6378 km). Since the moon does not describe an exact circular path around the earth, one calculates minus the mean major semi-axis . The following applies  = 384,400 km - 4670 km = 379,730 km. This results in the mass ratio ${\ displaystyle r_ {1}}$${\ displaystyle r_ {2}}$ ${\ displaystyle r_ {1}}$${\ displaystyle r_ {2}}$

${\ displaystyle {\ frac {r_ {1}} {r_ {2}}} \ approx {\ frac {1} {81 {,} 3}}.}$

The mass of the moon is therefore about 181 of the mass of the earth. Inserting the earth's mass M ≈ 5.97 · 10 24  kg results in the mass of the moon

${\ displaystyle m \ approx {\ frac {M} {81 {,} 3}} \ approx 7 {,} 34 \ cdot 10 ^ {22} {\ text {kg}}}$.

More precise measurements on site result in a value of m ≈ 7.349 · 10 22  kg.

### Magnetic field of the moon

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

#### Local magnetic fields

##### Interaction with the solar wind

The solar wind and sunlight create magnetic fields on the side of the moon facing the sun. Ions and electrons are released from the surface. These in turn influence the solar wind.

##### Magcons

The rare "moon vortices" without relief, so-called swirls , are noticeable not only because of their brightness but also because of a magnetic field anomaly. These are called Magcon ( Mag netic con called centration). There are different theories about their origin. One of them is based on large antipodal impacts, from which plasma clouds ran around the moon, met on the opposite side and there permanently magnetized the iron-rich lunar soil. According to another idea, some of the anomalies could also be remnants of an originally global magnetic field.

## Geology of the moon

In the area of ​​the day-night boundary , the craters are particularly easy to see.

### Origin of the moon

Differentiation of the outer layers of the moon:
KREEP : K alium , R are E arth E lements (Eng. Rare earths ), P hosphorus

With 3476 km, the moon has about a quarter of the diameter of the earth and has a lower mean density than the earth with 3.345 g / cm 3 . 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 in comparison to Earth, remained unexplained for a long time and gave rise to numerous theories about the origin of the moon.

The model for the formation of the moon, which is widely recognized today, states that about 4.5 billion years ago the protoplanet Theia , a celestial body the size of Mars , collided with the proto-earth almost grazingly . 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 clumped together and finally formed the moon. Most of the impactor combined 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. It formed Mare , which later completely cooled only a few hundred million years. The so-called last major bombardment did not end until 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 group of researchers from ETH Zurich and the Universities of Münster, Cologne and Oxford were able to precisely date the formation of the moon for the first time. 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. Recent studies by German scientists, which take into account the crystallization behavior of the magma ocean, come to an age of 4425 ± 25 million years.

### internal structure

Model of the shell structure of the moon:
▪ yellow: core
▪ orange: inner / lower coat
▪ blue: outer / upper coat (in the text: outer + middle coat)
▪ gray: crust
Schematic structure of the moon

The knowledge about the inner 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 as well as tremors caused by impacts by meteoroids and by explosions triggered especially for this purpose. These records allow conclusions to be drawn about the spread of seismic waves in the lunar body and thus about the structure of the interior of the moon, whereby the small number of measuring stations only provides very limited insights into the interior of the moon. The surface geology, which was already roughly known through observations from the earth, was obtained from the lunar rock samples brought to earth by the Apollo and Luna missions and from detailed maps of the geomorphology, the mineral composition of the lunar surface and the gravitational field in the context of the clementine - and the Lunar Prospector mission gained new knowledge.

Seismically, the anorthosite lunar crust (mean rock density 2.9 g / cm 3 ) on the front of the moon can be demarcated from the mantle at an average depth of 60 km. On the back it probably extends to a depth of 150 km. The greater thickness of the crust and thus the increased proportion of relatively light feldspar-rich crustal rock on the remote side could be at least partially responsible for the fact that the moon's center of mass is about 2 km closer to the earth than its geometric center. Below the crust there is an almost completely solid mantle of mafic and ultramafic rock ( olivine and pyroxene-rich cumulates ). Between mantle and crust a thin layer of basaltic composition suspected that was enriched in the crystallization of the other two rocks Cases with incompatible elements, and therefore a high proportion of K alium , R are E arth e lements (dt. REE ) and P hosphor comprising . This special chemical signature, which is also characterized by high concentrations of uranium and thorium , is called KREEP . According to traditional hypotheses, this so-called original KREEP layer occurs evenly distributed below the lunar crust. According to more recent findings obtained from data from the Lunar Prospector probe, KREEP seems to have accumulated during the differentiation of crust and mantle mainly in the crust of today's Oceanus-Procellarum - Mare-Imbrium region. The heat production by the radioactive elements is made responsible for the suspected "young" volcanism in this lunar region (up to 1.2 billion years before today).

The seismic exploration of the moon yielded indications of discontinuities ( discontinuities ) at depths of 270 and 500 km, which are interpreted as interfaces between differently composed rock envelopes and therefore as the boundaries between upper and middle (270 km) or middle and lower (500 km) lunar mantle be valid. In this model, the upper mantle is interpreted as quartz-bearing pyroxenite, the middle as FeO- enriched olivine-bearing pyroxenite and the lower mantle as olivine-orthopyroxene-clinopyroxene-garnet association. But other interpretations are also possible.

Little is known about the lunar core and different views exist about its exact size and properties. Through extensive processing of seismic data, it has now been determined that the lunar core with a radius of about 350 km is approximately 20% the size of the moon (cf. earth core relative to the size of the earth: ≈ 50%) and thus the mantle-core boundary located at a depth of about 1400 km. It is believed that, like the Earth's core, it is mainly made of iron. The seismic data (including the damping of shear waves ) provide indications that a solid inner core is surrounded by a liquid outer core, which in turn is adjoined to the outside by a partially molten boundary layer (PMB ). This model can be used to derive the approximate temperatures that must prevail in the core of the moon, which are significantly below those of the earth's core, around 1400 ° C (± 400 ° C). The lowest mantle and core with their partially melted or liquid material are collectively referred to as the lunar asthenosphere . The areas above (middle and upper mantle and crust), which are apparently completely rigid and in which there is no damping of shear waves, form the lunar lithosphere .

#### Moonquake

The seismometers left behind from the Apollo missions recorded around 12,000 moonquakes by the end of the measurements in 1977. With a magnitude of almost 5, the strongest of these earthquakes only reached a fraction of the magnitude of the strongest earthquakes. Most moonquakes had magnitudes of around 2. The seismic waves of the quakes could be followed for one to four hours. So they were only very weakly attenuated in the interior of the moon .

In more than half of the quakes, the hypocenter was at a depth of 800 to 1000 km, above the lunar asthenosphere. These earthquakes occurred mainly during apogee and perigee passage, that is, every 14 days. In addition, earthquakes with a near-surface hypocenter are known. The cause of the quakes are tidal forces that fluctuate with the distance from the earth . Deviations from the mean tidal potential are large at the points closest to and furthest away from the moon. However, the hypocenters of the quakes were not evenly distributed over an entire shell. Most of the earthquakes occurred in only about 100 zones, each only a few kilometers in size. The reason for this concentration is not yet known.

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

#### Mass concentrations

By unusual influences on the paths of the Lunar Orbiter missions gave the late 1960s, the first evidence of gravity anomalies that you mascons ( Mas s con cent rations , mass concentrations) called. 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.

### Regolith

Relative proportions of different elements on earth and moon (Maria or Terrae)

The moon has only a very small atmosphere . Therefore proposing to date constantly meteoroids of various sizes without braking on the surface, which the lunar surface at the upcoming smashed crustal rocks, have pulverized so literally. This process creates moon regolith (sometimes also referred to as lunar soil , "moon earth"). It covers large areas of the moon's surface with a layer several meters thick, which hides details of the original geology of the moon and thus makes it difficult to reconstruct its history.

Orange Soil : striking orange volcanic glass particles recovered from Apollo 17
Average chemical composition of the regolith
element corresponds to
oxide
Share (wt.%)
Maria Terrae
silicon SiO 2 045.4% 045.5%
aluminum Al 2 O 3 014.9% 024.0%
Calcium CaO 011.8% 015.9%
iron FeO 014.1% 005.9%
magnesium MgO 009.2% 007.5%
titanium TiO 2 003.9% 000.6%
sodium Na 2 O 000.6% 000.6%
potassium K 2 O < 00.1% < 00.1%
Total 100% 100%

Although it is commonly referred to as moondust , 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.

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. 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, i.e. regolith grains baked by glass. In some places, these make up almost half of the surface rock of the moon and arise when the splashes of molten rock generated by the impact do not solidify until they hit the regolith layer.

In lunar meteorite Dhofar 280 , of 2001, Oman was found new ones were iron - silicon -Mineralphasen identified. One of them (Fe 2 Si), thus clearly demonstrated in nature for the first time, was named after Bruce Hapke as Hapkeit . In the 1970s, he had predicted the formation of such iron compounds through space weathering. Space erosion also changes the reflective properties of the material and thus affects the albedo of the lunar surface.

The moon has no appreciable magnetic field; H. 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 in integrated circuit manufacture . 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 a meter into the moon's surface and forms unstable nuclides there through nuclear reactions (mainly spallation reactions ) . These transform u. a. through alpha decay with different half-lives into stable nuclides. Since a helium atomic nucleus is formed during each alpha decay, the 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.

### water

The moon is an extremely dry body. However, with the help of a new method, scientists were able to detect tiny traces of water (up to 0.0046%) in small glass spheres of volcanic origin in Apollo samples in summer 2008 . This discovery suggests that after the massive collision that created the moon, not all of the water evaporated.

For the first time in 1998 the Lunar Prospector probe found evidence of water ice in the craters of the polar regions of the moon, this is evident from the energy spectrum of the neutron flux. This water could come from comet crashes. Since the deeper areas of 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, however, failed.

In September 2009, reflection minima in the 3 µm range of infrared spectra of the lunar surface, which the NASA instrument Moon Mineralogy Mapper ( M 3 for short ) had recorded on board the Indian probe Chandrayaan-1 , provided indications of “water and hydroxyl ” close to the surface shaded areas of the two lunar poles. This phenomenon was already detected during the instrument calibration of the Cassini space probe during its flyby on the moon in 1999.

Subsequently, in the course of the evaluation of further M 3 data, at least part of this material was “definitely” identified as water ice.

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.

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 0.6% water. The water has a hydrogen isotope ratio , which deviates significantly from the values ​​of terrestrial water.

In October 2010, a further analysis of the LCROSS and LRO data revealed that there is much more water on the moon than previously assumed. The Chandrayaan-1 probe found evidence of at least 600 million tons of water ice at the north pole of the moon alone. Hydroxyl ions, carbon monoxide, carbon dioxide, ammonia, free sodium and traces of silver were also detected.

Near the surface, water (ice) survives longest at the poles of the moon , as these are least illuminated and heated by sunlight, and especially in the depths of craters. By examining with neutron spectrometers in orbit, Matthew Siegler et al. the highest concentrations of hydrogen (probably in the form of water ice) slightly off the current poles in two locations that are diametrically opposite each other. From this they derive the hypothesis that - for example due to volcanic mass displacement - the polar axis has shifted by about 6 ° .

## Surface structures

Topography of the near-earth (left) and far-earth sides of the moon relative to the lunar geoid
The moon, shining silver in the night sky, is actually dark gray (low albedo ); here the back of the moon in front of the much brighter, blue / white earth ( DSCOVR , Aug. 2015)

The surface of the moon measures 38 million km 2 and is 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 moon's eloquent "silver shine" is only faked to an earthly observer by the contrast to the night sky. In fact, the moon even has a relatively low albedo (reflectivity), which only becomes clear when it is viewed from the outside, such as from the Deep Space Climate Observatory (DSCOVR, see photo, which shows the even brighter back of the moon ).

The lunar surface is divided into Terrae and Maria . The Terrae are extensive highlands and the Maria are large basin structures that are framed by mountain ranges and in which there are wide plains of solidified lava. Both the Maria and the Terrae are littered with craters . There are also numerous trenches and grooves as well as shallow domes, but no active plate tectonics like on Earth. On the moon, the highest peak rises 16 km above the bottom of the deepest depression, which is around 4 km less than on earth (including ocean basins).

### Maria

Mare Imbrium with the large Copernicus crater at the top of the picture (Apollo 17, Dec. 1972)

The near-Earth side of the moon is shaped by the most and largest of Maria . The Maria are dark plains that cover a total of 16.9% of the lunar surface. They cover 31.2% of the front and only 2.6% of the back. Most of the Maria are grouped conspicuously in the northern half of the near-earth side and form the popularly so-called " moon face ". In the early days of lunar exploration, the dark Maria was thought to be seas; therefore, after Giovanni Riccioli , they are referred to as Maria (singular: Mare ), the Latin word for seas.

The Maria are solidified basaltic lava ceilings inside extensive circular basins and irregular depressions. The depressions were probably created by large impacts in the early moon phase. Since the lunar mantle was still very hot in the early phase and therefore magmatically active, these impact basins were then filled with rising magma or lava. This was presumably strongly favored by the lower crust thickness of the near-earth moon side compared to the far-earth moon side. However, the extensive volcanism of the front of the moon has probably been favored by other factors (see KREEP ). The Maria have only a few large craters, and outside the craters their heights vary by a maximum of 100 m. These small elevations include the dorsa . The dorsa bulge flat as a back and extend over several dozen kilometers. The Maria are covered by a 2 to 8 m thick layer of regolith rich in iron and magnesium . (See also: List of planes of the earth's moon )

Samples of their dark basalts have radiometrically dated the Maria to 3.1 to 3.8 billion years. The youngest volcanic moon rock is a meteorite found in Africa with the KREEP signature, which is approx. 2.8 billion years old. However, the density of craters in the Maria does not match this, which points to a sometimes significantly lower geological age of the Maria of "only" 1.2 billion years.

#### Irregular Mare Patches

After evaluating images and surface data from the Lunar Reconnaissance Orbiter , a team of scientists from Arizona State University and the Westphalian Wilhelms University of Münster proposed in October 2014 that there was widespread volcanic activity on the moon well less than 100 million years ago could have given. According to this, numerous smaller structures with dimensions between 100 m and 5 km exist within the large Maria, which are called Irregular Mare Patches and interpreted as local lava blankets. The small size and density of the impact craters in these “patches” indicate that they are very young for lunar conditions, sometimes barely more than 10 million years. One of these structures, called “Ina”, had been known since the Apollo 15 mission, but was previously regarded as a special case with little informative value for the geological history of the moon. The now ascertained frequency of the irregular mare patches allows the conclusion that the volcanic activity on the moon did not, as previously assumed, "abruptly" end about a billion years ago, but slowly weakened over a long period of time, which, among other things, was the previous one Questions models of temperatures inside the moon.

### Terrae

The highlands used to be seen as continents and are therefore referred to as terrae . They have significantly more and larger craters than the Maria and are covered by a regolith layer up to 15 m thick, which is rich in light anorthosite rich in aluminum . The oldest highland anorthosite specimens have been dated radiometrically using the samarium - neodymium method to a crystallization age of 4.456 ± 0.04 billion years, which is interpreted as the age of formation of the first crust and the beginning of the crystallization of the original magma ocean. The youngest anorthosites are around 3.8 billion years old.

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

### crater

 Theophilus Crater (Apollo 16, NASA) Rima Hadley (Apollo 15, NASA)

The moon craters were created by the impact of cosmic objects and are therefore impact craters . The largest of them were formed about 3 to 4.5 billion years ago in the early period of the moon by impacts of large asteroids . They are, the nomenclature follows from Riccioli, preferably named for astronomers, philosophers and other scholars. Some of the large impact craters are surrounded by star-shaped radiation systems . These rays come directly from the impact and consist of ejecta (so-called ejecta ) that has solidified into numerous glass spheres . The glass spheres prefer to scatter the light back in the direction of incidence, whereby the rays stand out brightly from the darker regolith when the moon is full. The rays are particularly long and noticeable at Tycho Crater .

The largest impact crater on the moon is the South Pole Aitken Basin , which measures 2240 km in diameter. The smallest are micro-craters that only become visible under the microscope. On the front of the moon, more than 40,000 craters measuring more than 100 m in diameter are visible with terrestrial telescopes alone. The crater density is significantly higher on the rear side, as its surface is geologically older on average (see also: List of craters on the Earth's moon ) .

Volcanic craters have not yet been clearly identified. Since the lunar crust has a lower proportion of SiO 2 than the continental crust, no stratovolcanoes have formed there, as they are e.g. B. are typical of the Pacific Ring of Fire on Earth. But shield volcanoes with a central caldera, such as those found in the Earth's ocean basins or on Mars, do not seem to exist on the moon. Instead, lunar volcanism apparently took place predominantly in the form of crevice eruptions .

### Grooves

On the lunar surface there are also groove structures (rimae), the origin of which had long been speculated 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 tubes whose roof has collapsed. High-resolution satellite photos and double radar echoes from the lunar surface in the Marius Hills ( Oceanus-Procellarum Basin ), where a negative gravity anomaly was also registered, make it very likely that there are still extensive intact lava tube systems today.

The origin of the straight grooves is much less clear - it could be shrinkage cracks that have formed in the cooling lava.

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

### Pits or holes

"Hole" in the lunar surface of the Marius Hills region

In 2009, the astronomer Junichi Haruyama and his work group discovered for the first time a "black hole" with a diameter of approx. 65 m in the lunar surface in the area of ​​the Marius Hills in Oceanus Procellarum on the Earth-facing side of the moon in images of the lunar probe Kaguya . It lies approximately in the middle of a shallow groove of the meandering type. Nine different images, taken from different angles and with different positions of the sun, allowed an estimate of the depth of the hole to be 80 to 88 meters.

Since there is no apparent material that has flowed out around the hole, the formation of a volcanic shaft crater is excluded. Most likely it is a so-called skylight of a lava tube , which must have arisen because the ceiling of the lava tube collapsed at this point. The shallow groove therefore represents a lava tube, the ceiling of which is still largely intact, but topographically lies somewhat below the level of the surrounding area. The reason for the formation of the skylight could have been moonquakes, impacts from meteorites or the load of a still liquid lava flow. An influence of earthly gravity ( tidal forces ) is also conceivable.

By 2011, two other possible skylights had been discovered. At the beginning of 2018, the number of skylight candidates was around 200.

### Moon back

Back of the moon ( Mare Moscoviense above left )
Rotation of the moon viewed from the sun

Nothing was known about the back of the moon before the first space missions, as it is not visible from Earth; only Lunik 3 delivered the first pictures. The back differs from the front in several ways. Its surface is shaped almost exclusively by highlands rich in craters. The craters also include the large South Pole Aitken Basin , which is 13 km deep, 2240 km in diameter, and is overdrawn by many other craters. As studies of the Clementine mission and the Lunar Prospector have suggested, a very large impact body pierced the lunar crust and possibly exposed mantle rocks. At 150 km, the rear side crust is roughly twice as thick as the 70 km of the front side crust. The LRO space probe also discovered trench structures on the back . There is also the highest known point on the moon (10,750 m), which was measured with the laser altimeter of the Kaguya space probe and is on the edge of the Engelhardt crater. On January 3, 2019, a space probe, the Chang'e-4 , landed on the back of the moon for the first time .

The back and front have also developed differently because the geometric lunar center (center of the sphere of equal volume) and its center of gravity are 1.8 km (1 per thousand of the lunar radius) apart. This asymmetry of internal structure and lunar crust could result from a collision with a second satellite , which some researchers assume in the early days of the moon.

For the far side of the moon the "dark side of the moon" is (English darkside of the Moon ) is a preserved figure of speech , but this is only to be understood symbolically in terms of an unknown side; In the actual sense of the word, the phrase is wrong, because - as already noted about the moon phases - the back and front 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 back is even significantly lighter than the front.

## Influences on the earth

Earthrise : Earth and Moon as seen from Apollo 8
Moon and Earth from a space shuttle seen from

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 earth's rotational movement 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 earth's rotation will be tied to the lunar orbit , and the earth will always turn the same side to the moon.

The earth is not perfectly spherical, but flattened by the rotation. The tidal force of the sun and moon creates a righting torque that is maximum twice a year or monthly. As a top, the earth does not follow this directly, but precesses with a first approximation of a constant inclination of the earth's axis. If the sun were the only cause of precession, the inclination of the earth's axis would change over wide areas within millions of years. This would mean unfavorable environmental conditions for life on earth, because the polar night would alternately cover the entire northern and southern hemisphere. The rapid precession caused by the moon stabilizes the inclination of the earth's axis. In this way the moon contributes to the life-promoting climate of the earth.

### Influence on living beings

According to the Skeptic's Dictionary , no evaluated scientific study has shown a significant positive correlation between the phases of the moon and the occurrence of sleep disorders, traffic accidents, surgical complications, the frequency of suicidal acts or the frequency of births. Some people, e.g. B. in agriculture and forestry , have always made sure that certain work in nature is done in the "correct" moon phase ( see also: moon wood , lunar calendar ).

The daily movement of the moon and the information it contains about the cardinal points is used by migratory birds and some species of nocturnal insects for navigation . In some species of annelids (such as the Samoa Palolo ), crabs and fish ( Leuresthes ), the reproductive behavior is very closely linked to the monthly phase change of the moon.

The correlation between the position of the moon and the weather, which was researched as early as the 18th century, is so low that the influence it has on living beings can be completely neglected.

The Sleepwalking of people is misleading as Moonstruck-being interpreted.

### Lunar rainbow

Mondhof
22 ° moon halo on October 23, 2010, seen from Graz ( Austria )

At night, when moonlight and raindrops meet , a lunar rainbow can arise, which works analogously to the physical principle of the sun's rainbow .

### Mondhof and Mondhalo

As Mondhof colored rings are referred to the moon caused by the diffraction of the light on the water droplets of the clouds are caused. The outermost ring is reddish in color and has an extension of about two degrees, in rare cases up to ten degrees.

Colloquially, the term of the moon court is also used for a halo around the moon. Ice crystals in layers of air are responsible for this, which have arisen from thin high-altitude fog or haze and deflect the light falling on the earth at a very weak angle and thus create a kind of glowing ring effect for the viewer.

A special halo phenomenon of the moon is the side moon . Similar to the suns , minor moons appear at a distance of around 22 degrees next to the moon. Because of the lower light intensity of the moon, you see them less often and mostly when the moon is full.

### Moon illusion and "false" moon tilt

Moon rise in the evening on the eastern horizon. The subjectively perceived size of the moon depends u. a. on the comparison values. Compared to the trees on the horizon, it looks big. Compared to the branches of the high willow in the front right, it appears small.

The moon illusion is the effect that the moon looks larger near the horizon than at the zenith . This is not a result of the refraction of light in the air layers, but an optical illusion that is examined and explained by the psychology of perception .

The phenomenon that the illuminated side of the moon often does not seem to point exactly to the sun is an optical illusion and is explained there under the heading Relativity of the viewing angle . You can convince yourself that the illuminated crescent moon is actually - as expected - always perpendicular to the connecting line between sun and moon by making this connecting line visible through a string stretched between sun and moon with outstretched arms.

## History of moon observation

### Open-eyed observation, lunar orbit and eclipses

After the sun, the moon is by far the brightest object in the sky; at the same time, its unique brightness and phase change between full moon and new moon can also be observed very well with the naked eye. The first appearance of the crescent moon in the evening sky (" new light ") marks the beginning of the respective month in some cultures .

The phases of the moon and the solar or lunar eclipses were certainly observed by humans from an early age. The exact length of the sidereal and synodic months was already in the 5th millennium BC. Known as well as the inclination of the lunar orbit towards the ecliptic (5.2 °). At least 1000 BC The Babylonian astronomers knew the conditions under which solar eclipses would occur and the prediction of the solar eclipse of May 28, 585 BC. Chr. By Thales of Miletus chose 585 v. The war between the Lydians and Medes . From Anaxagoras the statement is handed down that the moon receives its light from the sun and that there are valleys and ravines on it; these and other teachings earned him a conviction for blasphemy .

The details that can be clearly seen on the moon (see moon face ) are also known as rabbits etc. in other cultures . The dark, sharply delimited areas were interpreted as seas early on (these smooth plains are therefore still called mare today), while the nature of the radiation systems that become visible during a full moon could only be clarified in the 20th century.

### Observation with telescope, lunar maps and space travel

As the celestial body closest to the earth, the moon shows topographical details through simple telescopes , especially near the terminator , since the shadows are long there. So soon after the invention of the telescope in 1608, the exploration of the moon began, including Galileo Galilei , David Fabricius , Thomas Harriot and Simon Marius . The highlights of selenography were the work of Johann Hieronymus Schroeter , who published his seleno topography in 1791 , the precise mapping of the lunar craters and mountains as well as their names.

Daguerreotype of the waning crescent from 1840

In March 1840 reach John William Draper in New York City with a counter to the Earth's rotation carried Telescope of New York University , the first photographic images of the moon.

This was followed by the era of high-precision lunar maps by Beer, Mädler and others, from around 1880 long-focal length astrophotography (see also Paris lunar atlas ) and the first geological interpretations of the lunar structures. The increased interest in the moon due to space travel (first lunar orbit 1959) led to the first observation of glowing gas escapes by Kosyrew , but the volcanic theory of the lunar craters had to give way to the interpretation as impact craters . The preliminary high points were the manned moon landings 1969–1972, which enabled centimeter-accurate laser distance measurements and, in recent years, multispectral remote sensing of the moon's surface and the precise measurement of its gravitational field by various lunar orbiters .

### Mythological beginnings

Nebra Sky Disc

The oldest known representation of the moon is a 5000 year old lunar map from the Irish Knowth . Another historically significant figure in Europe is the Nebra Sky Disc .

The stone monument Stonehenge probably served as an observatory and was built in such a way that special positions of the moon could also be predicted or determined.

In many archaeologically examined cultures there are indications of the great cultic significance of the moon for the people of that time. The moon usually represented a central deity , as a female goddess, for example with the Thracians Bendis , with the ancient Egyptians Isis , with the Greeks Selene , Artemis and Hecate as well as with the Romans Luna and Diana , or as a male god like for example the Sumerians Nanna , in Egypt Thoth , in Japan Tsukiyomi , with the Aztecs Tecciztecatl and with the Germans Mani . The sun and moon were almost always thought of as having the opposite sex, even if the assignment varied. In China, on the other hand, the moon was a symbol of the west, autumn and femininity ( yin ).

A frequently occurring motif is the image of the three faces of the moon goddess: with the waxing moon the seductive virgin full of sexuality, with the full moon the fertile mother and with the waning moon the old woman or the witch with the strength to heal, for example with the Greeks Artemis, Selene and Hecate as well as Blodeuwedd , Morrígan and Ceridwen among the Celts .

The moon as a heavenly body is the subject of novels and fictions , from Jules Verne's double novel From Earth to the Moon and Journey Around the Moon to Paul Lincke's operetta Frau Luna and Hergé's two-volume Tintin - comic adventure travel destination moon and steps on the moon up to the futuristic idea of ​​a settlement on the moon or the travel guide Reisen zum Mond by Werner Tiki coastal maker .

### Calendar invoice

In addition to mythological worship, people used the regular and easily manageable rhythm of the moon very early on to describe periods of time and as the basis of a calendar ; the Islamic calendar is still based on the lunar year with 354 days (12 synodic months). With the transition to arable farming , the importance of the course of the year for sowing and harvesting became more important. In order to take this into account, leap months were inserted first as required, later according to fixed formulas such as the metonic cycle , which synchronized the lunar year with the solar year. The ancient Greek and Jewish calendars , for example, are based on this lunisolar scheme .

The length of a week of seven days that is still in use today is probably based on the chronological sequence of the four main phases of the moon (see above). In the Easter calculation , the moon age on the last day of the previous year plays a role and is called epacts .

Of the ancient civilizations , only the ancient Egyptians had a pure solar year with twelve months of 30 days and five leap days, i.e. without any strict reference to the synodic month of 29.5 days, presumably because for the Egyptian culture the exact prediction of the Nile floods and thus the course of the solar year was necessary for survival.

## Research history

Scientific sub-disciplines that deal with the study of the moon have names formed from the Greek word for moon, Σελήνη ( Selene ). There are:

• Selenology , also called " 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.
• Selenography is the recording and designation of surface structures of the moon, in particular the creation of lunar maps .
• Selenodesia , deals with the measurement of the moon and its gravitational field.

### Earthbound exploration

The earliest rough lunar map with outlines of the albedo features and the first attempt at nomenclature was sketched by William Gilbert in 1600 based on the naked eye. The first, even if only sketchy, representation of the moon structures visible with a telescope comes from Galileo Galilei (1609), the first useful ones come from Johannes Hevelius , who is considered the founder of selenography with his work Selenographia sive Lunae Descriptio (1647) . In the nomenclature of the lunar structures, the system of Giovanni Riccioli prevailed, who in his maps of 1651 named the darker regions as seas ( Mare , plural: Maria ) and the craters after philosophers and astronomers . However, this system has only been generally recognized since the 19th century.

Drawn moon map from 1881 ( Andrees Handatlas )

Thousands of detailed drawings of moon mountains , craters and whale planes were made by Johann Hieronymus Schroeter (1778–1813), who also discovered many moon valleys and grooves. Wilhelm Beer and Johann Heinrich Mädler published the first lunar atlas in 1837, and it was soon followed by a long series of photographic atlases .

At the end of the 19th century, statements about the appearance of the moon could be made that are still largely valid today. The Austrian geologist Melchior Neumayr made the following statement in this regard:

"There are three phenomena in particular that give the moon an extremely strange, strange physiognomy: the absence of an atmosphere, the absence of water on the surface and the predominance of crater-shaped ring mountains in the surface design."

- Melchior Neumayr : Earth History , 1895

However, the actual formation of these craters was still uncertain up to this point. As a result, Neumayr assumed volcanism as the most likely cause:

"By far the most widespread are ring-shaped mountains, which in their whole formation are most strikingly reminiscent of our earthly volcanoes, and it is generally assumed that these structures are in fact due to eruptive activity."

- Melchior Neumayr : Earth History , 1895

Neumayr states that individual mountains rise more than 8000 m above their surroundings. The determination of the height of craters, mountains and plains was very problematic with telescopic observations and was mostly done by analyzing shadow lengths, for which Josef Hopmann developed special methods in the 20th century. Reliable values ​​are only known through probe mapping: the craters, with diameters of up to 300 km, appear steep, but are only inclined by a few degrees, while the highest elevations reach a height of up to 10 km above the mean level.

### Exploration with the first spacecraft

The second great leap in advances in lunar research began three and a half centuries after the invention of the telescope with the use of the first lunar probes . The Soviet probe Lunik 1 came around 6000 km close to the moon, Lunik 2 finally hit it and Lunik 3 delivered the first images from its rear side . The quality of the maps was significantly improved in the 1960s, when the lunar orbiter probes used the lunar orbit probes to map them in preparation for the Apollo program . The most accurate maps today come from the 1990s through the Clementine and Lunar Prospector missions.

The US Apollo and the Soviet Luna programs brought a total of 382 kilograms of lunar rock from the front of the moon to earth with nine missions between 1969 and 1976 ; the following table gives an overview.

Map of the landing sites of the manned and unmanned missions up to 1976
Landing date mission amount Landing site
20th July 1969 Apollo 11 21.6 kg Mare Tranquillitatis
19th November 1969 Apollo 12 34.3 kg Oceanus procellarum
20th September 1970 Luna 16 100 g Mare Fecunditatis
5th February 1971 Apollo 14 42.6 kg Fra Mauro highlands
July 30, 1971 Apollo 15 77.3 kg Hadley Apennines (Mare and Highlands)
February 21, 1972 Luna 20 30 g Apollonius highlands
April 20, 1972 Apollo 16 95.7 kg Descartes
December 11, 1972 Apollo 17 110.5 kg Taurus -Littrow (Mare and Highlands)
18th August 1976 Luna 24 170 g Mare Crisium

In 1979 the first lunar meteorite was discovered in Antarctica , but its origin from the moon was only recognized a few years later by comparing it with the lunar samples. We now know more than two dozen more. These form a complementary source of information on the rocks that were brought to earth by the lunar missions: While the exact origin of the Apollo and Luna samples is known, the meteorites are likely to be more representative of the lunar surface, despite the lack of knowledge of their exact place of origin on the moon , as some should also come from the back of the moon for statistical reasons.

### People on the moon

Buzz Aldrin on July 21, 1969 (UTC / Apollo 11)
Eugene Cernan on December 11, 1972 with the moon rover

After the earth, the moon is the only celestial body that humans have entered. As part of the Cold War , the USA and the USSR undertook a race to the moon (also known as the "space race") and, in the 1960s, culminated in an attempt at manned moon landings , which were only realized with the United States' Apollo program were. The Soviet Union's manned lunar program was then canceled.

On July 21, 1969 UTC , Neil Armstrong, the first of twelve astronauts in the Apollo program, set foot on the moon. After six successful missions, the program was discontinued in 1972 because of the high costs; Eugene Cernan was the last person to leave the moon on December 14, 1972.

The following table lists the twelve men who stepped on the moon. All were citizens of the United States.

# Mission and date Astronauts
01. Apollo 11
July 21, 1969
Neil Armstrong (1930-2012)
02. Buzz Aldrin (born 1930)
03. Apollo 12
November 19th 1969
04th Alan Bean (1932-2018)
05. Apollo 14
February 5th 1971
Alan Shepard (1923-1998)
06th Edgar Mitchell (1930-2016)
07th Apollo 15
July 31, 1971
David Scott (* 1932)
08th. James Irwin (1930-1991)
09. Apollo 16
April 21, 1972
John Young (1930-2018)
10. Charles Duke (born 1935)
11. Apollo 17
December 11th 1972
Eugene Cernan (1934-2017)
12. Harrison Schmitt (* 1935)

In addition, a further twelve US space travelers from the Apollo program visited the moon, but without landing on it. These include the six pilots Michael Collins , Richard Gordon , Stuart Roosa , Alfred Worden , Ken Mattingly and Ronald Ellwin Evans of the command capsules waiting in lunar orbit, as well as the first-time visitors Frank Borman , Jim Lovell and William Anders with Apollo 8 on December 24, 1968, with Apollo 10 Tom Stafford with John Young and Eugene Cernan on their first flight to the moon, and with Apollo 13 again Jim Lovell and Jack Swigert and Fred Haise , who only made one swing-by maneuver on the moon due to a breakdown on the outbound flight .

Concrete plans for a return to the moon only emerged again through announcements by then US President George W. Bush and NASA in 2004. The resulting Constellation program was discontinued in 2010 due to missed deadlines and escalating costs and shortly afterwards replaced by the SLS / Exploration Mission program, which is plagued by the same problems. After the planned date for the next moon landing had been postponed to 2028, the government under Donald Trump took the initiative in 2019 and called for a return to the moon by 2024. This project, known as the Artemis program , is supposed to be "sustainable" and with a landing in the South Pole region kick off. The funds for this still have to be approved by the legislature.

In addition to NASA, the US company SpaceX is also planning manned moon landings with its " Starship " in the 2020s. Likewise, Russia, China and Japan would like to reach the surface of the moon with their own spaceships and space travelers in the 2030s.

### Lunar probes of recent times

After a break in the entire lunar voyage of a good 13 years, the Japanese experimental probe Hiten launched on January 24, 1990 without a scientific payload. On March 19 of the same year it launched its daughter probe Hagoromo in a lunar orbit, swung itself into a lunar orbit on February 15, 1992 and hit the moon on April 10, 1993.

On January 25, 1994, the American space probe Clementine went to the moon to test new devices and instruments. On February 19, 1994, it entered a polar lunar orbit and from there mapped about 95% of the lunar surface. In addition to the numerous photographs, it provided evidence of the occurrence of water ice at the lunar South Pole. In May of the same year, a faulty engine ignition prevented the planned onward flight to the asteroid Geographos . The probe has been out of service since June 1994.

On January 11, 1998, the US lunar probe Lunar Prospector reached a polar lunar orbit to investigate evidence of water ice at the poles. In addition, she also measured the lunar gravity field of the moon for a global gravity field map. On July 31, 1999 the mission ended with a planned impact near the lunar south pole in order to be able to detect water ice in the particle cloud ejected from the earth; however, this proof has not been successful.

As the first ESA lunar probe , SMART-1 tested new technologies and reached a lunar orbit on November 15, 2004. From there she looked for water ice, photographed the surface of the moon and mainly examined its chemical composition. The probe hit the moon on September 3, 2006, as planned, which could be observed from Earth.

On October 3, 2007, the Japanese probe Kaguya reached the moon and entered a polar orbit. The main orbiter had launched two auxiliary satellites in their own lunar orbit: a VRAD satellite was used for earth-based VLBI measurements and a relay satellite was responsible for transmitting the radio signals. The observation of the moon began in mid-December 2007 and ended on June 10, 2009 with Kaguya's intended impact.

On October 24, 2007, the People's Republic of China launched its first Chang'e-1 lunar probe . Chang'e-1 reached the moon on November 5th, and orbited it over the poles for about a year. She analyzed the lunar rocks spectroscopically and mapped the lunar surface three-dimensionally. A comprehensive microwave map of the moon was also created for the first time, which also shows mineral resources. Chang'e-1 hit the moon on March 1, 2009 ( see also: Lunar program of the People's Republic of China ). The original replacement probe from Chang'e-1 became the successor probe Chang'e-2 . It orbited the moon from October 6, 2010 to June 9, 2011. By April 2011, it deepened the success of the China National Space Administration and prepared the soft landing for Chang'e-3 .

The launch of the Indian lunar probe Chandrayaan-1 , and thus India's first space probe , took place on October 22, 2008. At the beginning of its mission on November 14, it had a lander hit hard from its polar orbit near the south lunar pole. With instruments from different countries, a mineralogical, a topographical and an elevation map of the moon were to be created. However, the contact broke off prematurely on August 29, 2009. The mission was originally supposed to last two years.

Representation of the LRO

On June 23, 2009 at 9:47 UTC, NASA's Lunar Reconnaissance Orbiter (LRO) entered a polar orbit to orbit the moon at an altitude of 50 km for at least one year, with data for the preparation of future landing missions win. The devices of the US probe provide the basis for high-resolution maps of the entire lunar surface (topography, orthophotos with 50 cm resolution, indicators for the occurrence of water ice) and data on cosmic radiation exposure. 5185 craters with a diameter of at least 20 km were recorded. From their distribution and age it was concluded that up to 3.8 billion years ago mainly larger chunks hit the moon, after that mainly smaller ones. The LRO space probe also discovered trench structures on the back of the moon. It is not yet known when the mission will end.

The same launcher was used to send the Lunar Crater Observation and Sensing Satellite (LCROSS) to the moon. It hit the Cabeus Crater near the South Pole on October 9th . The satellite consisted of two parts, the burned-out upper stage of the rocket, which created a crater, and the device unit, which was decoupled some time before the impact and which analyzed the thrown particle cloud, particularly with regard to water ice, before it also hit four minutes later.

Representation of the two GRAIL probes in lunar orbit

From March 7, 2012, two orbiters launched by NASA on September 10, 2011 orbit the moon under the name Gravity Recovery and Interior Laboratory (GRAIL) in order to jointly measure its gravity field more precisely. The mission ended on December 17, 2012, and both orbiters hit the lunar surface in a controlled manner.

On September 6, 2013, NASA launched the Orbiter Lunar Atmosphere and Dust Environment Explorer (LADEE) as the first mission of the new Lunar Quest program , which examined the atmosphere and dust of the moon in more detail. The mission was also used to test a laser as a new means of communication instead of radio waves. The mission ended on April 18, 2014, after a one-month extension, when the probe hit the lunar surface.

On December 14, 2013, the Chinese space agency made its first soft moon landing with Chang'e-3 . The approximately 3.7 tons heavy probe is used u. a. the transport of a 120 kg lunar rover, which receives its energy from radioisotope generators or is equipped with radionuclide heating elements so as not to freeze during the 14-day lunar night.

Two landing attempts in 2019 with the Israeli Beresheet probe and the Indian Chandrayaan-2 mission failed.

### Planned lunar probes

In 2020, the Chang'e-5 return mission is planned as part of the People's Republic of China's lunar program . A space probe is supposed to bring 2 kg of lunar rock back to earth. Such a rehearsal mission, Chang'e-6, is scheduled to take place in 2023 at the earliest to bring material from the moon to earth.

Various companies from Germany, Japan, the USA and Israel are planning to launch privately financed lunar probes in 2020.

NASA has planned the Lunar Flashlight and other CubeSats for 2021 at the earliest , which will be launched as part of the Artemis 1 mission and, among other things, will investigate water ice deposits on the moon.

Russia is planning to use the lunar probe Luna 25 in 2021 . It is said to deploy twelve penetrators mainly for seismic surveys and to drop a lander to search for water ice in a crater near the lunar south pole. Further lunar missions Luna 26 to Luna 28 are also already being planned.

## Ownership

The Outer Space Treaty (Outer Space Treaty) of 1967 prohibits States to collect a claim ownership of space objects such as the moon. To date, this agreement has been ratified by 109 United Nations states and is now in force. Since the Outer Space Treaty only speaks of states, some interpret that this agreement does not apply to companies or private individuals. Therefore, 1979 was Moon Treaty (Agreement Governing the Activities of States on the Moon and Other Celestial Bodies) designed this from Outer Space Treaty to close left behind alleged loophole. The "Moon Treaty" draft explicitly addressed and excluded ownership claims by companies and private individuals (Article 11, paragraphs 2 and 3). For this reason, the "Moon Treaty" is often cited as an obstacle to land sales; only in fact this agreement was never signed or correctly ratified in the United Nations . Only five states, none of which are space-permissible, have tried to ratify it. 187 other states as well as the USA, Russia and China have neither signed nor ratified it. The "Moon Treaty" is therefore not in force in most countries around the world today. The voting states had too many concerns at the time that it might jeopardize the profitable use of the moon, and so the agreement was not ratified (and therefore not law). Some conclude that there is a legal basis for moon property sales. It should also be noted that the International Astronomical Union is not involved in the sale of celestial bodies.

In 1980, the American Dennis M. Hope registered his claims to the moon with the San Francisco Land Office . Since no one objected within the eight-year period, which is suspended under American law, and since the Outer Space Treaty explicitly does not prohibit such sales by private individuals in the USA, Hope sells the land through its Lunar Embassy, which was founded for this purpose . However, since the land office in San Francisco is not responsible for celestial bodies and Hope has interpreted both the law regulating such ownership claims and the text from the Outer Space Treaty in a very adventurous way, the "land certificates" he sells are practically worthless .

## Coordinate objects

In the libration points L4 and L5 of the earth-moon system there is a dust cloud each, the Kordylewskischen clouds .

## Another satellite

Other earth satellites are the subject of unconfirmed observational claims or hypotheses for past periods of time such as the time the moon was formed .

## Trivia

### Lunar colonization

NASA illustration for a study of how raw materials could be extracted from moon material and brought to flight speed (1977)

The establishment of permanent outposts and colonies on the moon was discussed before the invention of space travel and still plays a role in science fiction literature. In 1979, a NASA study on mining on the moon listed the technology development necessary for this.

### Search for extraterrestrial intelligence

The moon could also provide clues for the search for extraterrestrial civilizations . Scientists like Paul Davies believe that a search for artifacts and remnants of extraterrestrial technology on the lunar surface is beneficial.

### Did terrestrial microbes survive an extended stay on the moon?

It is possible that the camera housing of the Surveyor 3 probe recovered during the Apollo 12 mission contained microbes on the earth's satellite for 31 months and were then able to multiply. See Forward Contamination for details and doubts .

## literature

• Alexander Angermann: Does the moon have an influence on the surgeon? An examination based on hip replacement surgery . Munich 2011 DNB 1014972477 , (Dissertation University of Munich 2011, 55 pages online PDF, free of charge, 61 pages, 1 MB).
• Bernd Brunner: Moon. The story of a fascination. Kunstmann, Munich 2011, ISBN 978-3-88897-732-9 .
• Alan Chu, Wolfgang Paech, Mario Weigand: Photographic moon atlas. 69 lunar regions in high-resolution photos. Oculum, Erlangen 2010, ISBN 978-3-938469-41-5 .
• Thorsten Dambeck: The moon is shaking. In: Image of Science . No. 7, 2002, , pp. 48-53.
• Ulrike Feist: Sun, Moon and Venus: Visualizations of Astronomical Knowledge in Early Modern Rome (= Actus et Imago , Volume 10). Akademie-Verlag, Berlin 2013, ISBN 978-3-05-006365-2 (Dissertation University of Augsburg 2011, 259 pages).
• David M. Harland: Exploring the moon. The Apollo expeditions. 2nd Edition. Springer et al., Berlin et al. 2008, ISBN 978-0-387-74638-8 .
• Ralf Jaumann, Ulrich Köhler: The moon. Origin, exploration, space travel. Fackelträger, Cologne 2009, ISBN 978-3-7716-4387-4 (with a conversation by Buzz Aldrin and Thomas Reiter ).
• Josef Sadil: Focus on the moon. Illustrated by Gerhard Pippig. Urania, Leipzig / Jena / Berlin 1962 (original title: Cíl měsíc , translated by Max A. Schönwälder), DNB 454251394 , OCLC 65043150 .
• Elmar Schenkel, Kati Voigt (Ed.): Sun, Moon and Distance: Space in Philosophy, Politics and Literature , PL Academic Research, Frankfurt am Main 2013, ISBN 978-3-631-64081-4 .
• Werner Wolf: The moon in German popular belief. Buhl 1929.

media

Wiktionary: Moon  - explanations of meanings, word origins, synonyms, translations
Commons : Moon  album with pictures, videos and audio files
Wikibooks: Moon  - learning and teaching materials
Wikiquote: Moon  Quotes
Wikisource: Moon  - Sources and Full Texts
Wikivoyage: Moon  Travel Guide

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 This article was added to the list of excellent articles on May 17, 2004 in this version .