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Moon

Moon

Our solitary and prominent Moon orbits Earth at a mean distance of only 382,000 kilometers (236,840 miles). The nearest planet, Venus, is never closer than 40 million kilometers (25 million miles). The Moon's mass is just under one-eightieth that of Earth, its volume just over one-fiftieth; the difference mainly stems from the Moon lacking a large metallic iron core and therefore having a much lower overall density than Earth. Its low mass is responsible for the low surface gravity (one-sixth that at Earth's surface), popularly recognized in the jumping, bouncing gait of Apollo astronauts. The mass is much too low for the Moon to hold any significant atmosphereit is essentially in a vacuum or for its surface to have liquid water.

The surface area of the Moon is only about four times that of the land area of the United States. The Moon is not as large as any planet other than distant little Pluto but is of the same scale as the Galilean satellites of Jupiter. These moons are much smaller in comparison with the planet they orbit. Earth's Moon is very different in chemical composition and structureand probably originfrom any other body in the solar system.

Orbit and Rotation

The 29.53-day orbit provides us with the lunar phases, as well as the occasional eclipses of the Sun and the more frequent eclipses of the Moon. The orbit is tilted only slightly (5.1°) from the plane of the ecliptic , but because Earth itself has a tilted axis of rotation (23.5°), the Moon's orbit is tilted substantially with respect to Earth's equator. The Moon's own axial rotation period is exactly the same as its orbital period, and so it shows almost the same face to Earth continuously. It is not exactly the same face because of the tilt of the Moon's rotational axis (1.5°) to its orbital plane around Earth, and the slight ellipticity of that orbit (the position of the observer on Earth also has a slight effect). Altogether, only 41 percent of the Moon's surface is permanently invisible to observers on Earth.

The gravitational pull of the Moon provides the twice-daily tides on Earth as Earth spins under the Moon. The Moon is gradually receding because of the tidal effects. As the Moon recedes, its angular momentum increases, compensated by a decrease in the spin rate of Earth. Thus, Earth's day is increasing in length; 600 million years ago it was only about eighteen hours long. The Moon stabilizes the tilt of Earth's own axis of rotation over long periods of time, and this has been important for stabilizing climate and thus life habitats.

The Exploration of the Moon

Even to the naked eye the Moon's face has darker and lighter patches. Italian mathematician and astronomer Galileo Galilei used a telescope in 1610 to discover its rugged, varied, and essentially unchanging features. He distinguished the brighter areas as higher and more rugged, the darker as lower, flatter, and smoother. He called the former "terra" (meaning "land"; pl. "terrae") and the latter "mare" (meaning "sea"; pl. "maria"), although that is not what they are.

For three centuries the Moon remained an object of astronomical study, with the collection of data about its shape, size, movements, and surface physical properties, as well as mapping. Not until the middle of the twentieth century were observations and a combination of natural and terrestrial analogs advanced enough that the volcanic origin of its dark plains and the impact origin of its craters and basins could be considered as settled. In the 1960s, a program of geological mapping, using techniques such as crater counting and overlapping relationships, confirmed and elucidated the nature of geological units and the order in which they were produced.

The study of the Moon reached peak activity in the space age, when spacecraft sent back detailed information from orbiters, hard-landers , and soft-landers (mainly from 1959 to 1970), and Apollo astronauts conducted experiments and made observations from equatorial orbit and at the surface (from 1968 to 1972). Six Apollo missions and three robotic samplereturn

BASIC DATA ABOUT THE MOON
Greatest distance from Earth 406,697 km
Shortest distance from Earth 356,410 km
Eccentricity of orbit 0.0549
Rotation period (synodic month) 29.53 Earth days
Rotation period (sidereal month) 27.32 Earth days
Mean orbital inclination to ecliptic 5° 08' 43"
Inclination of rotation axis to orbit plane 1° 32'
Mean orbital velocity 1.68 km/s
Period of revolution of perigee 3,232 Earth days
Regression of the nodes 18.60 years
Mass 7.35 × 1022 kg
Mean Density 3.34 g/cc
Surface gravity 1.62 m/s2
Escape velocity 2.38 km/s
Mean diameter 3,476 km
Mean circumference 10,930 km
Surface area 37,900,000 km2
Albedo (fraction light reflected) terrae 0.11-0.18
Albedo (fraction light reflected) mare 0.07-0.10
Mean surface temperature day 107°C
Mean surface temperature night -153°C
Mean surface temperature at poles: light -40°C
Mean surface temperature at poles: dark -230°C

vehicles collected samples of the Moon (from 1970 to 1976). Samples are particularly useful for understanding the processes that created the rocks and for the dating of events using radiogenic isotope techniques . Two flybys by the Galileo mission* to Jupiter (in 1990 and 1992), the Clementine lunar polar orbiter (in 1994) and the Lunar Prospector polar orbiter (in 1998) have provided substantially more global imaging, topographic, chemical, and mineralogical data.

Global and Interior Characteristics

The Moon is nearly homogeneous, as shown by its motions in space, and by the fact that rocks near the surface are not much different in density from the Moon as a whole. Nonetheless, samples show that the Moon was thoroughly heated at its birth about 4.5 billion years ago, possibly to the point of total melting, and then quickly solidified to produce a comparatively thin (60 to 100 kilometers [37 to 62 miles]) crust of slightly lighter material. This structure was confirmed by seismic experiments performed on the early Apollo missions. There may be an iron core, but if so it is very tiny, and there is no significant magnetic field.

Samples show that the Moon is very depleted in volatile elements (those that form gases and low-temperature boiling-point liquids), to the extent that it lacks any water of its own at all, even bonded into rocks. Water delivered to the Moon by cometary impact might exist, frozen in crater floors near the poles. The Moon is very reduced chemically, such that iron metal exists, but rust (oxidized, ferric iron) does not. The Moon is very depleted in the siderophile elements ("iron-loving") that go with metallic iron into a core, except for the surface rubble to which such elements have been delivered by eons of meteorite impact.

The Uppermost Surface of the Moon

The Moon has been bombarded by meteorites ranging in size from numerous tiny dust particles to rare objects hundreds of kilometers in diameter. The surface is covered everywhere with a thin fragmental layer (known as soil, or "regolith") that consists mainly of ground-up and remelted lunar rocks, with an average grain size of less than 0.1 millimeters (0.004 inch). This soil contains pebbles, cobbles, and even boulders of lunar rocks. A small percentage of the regolith consists of the meteoritic material that did the bombarding. The regolith is about 5 meters (16.5 feet) thick on basalts that were poured out about 3 billion years ago, while older surfaces have even thicker regoliths. This regolith layer, exposed to cosmic radiation and the solar wind , contains materials, such as hydrogen, that do not reach the surface of Earth because of its protection by both a magnetic field and an atmosphere.

The Older Crust of the Moon

Much of the crust consists of material that formed within a few tens of millions of years of the Moon's origin, partly by the floating of light (in both density and color) feldspar minerals , which crystallized from a vast ocean of silicate magma. The magma formed because of the Moon's rapid formation, and because of the generation of radioactive heat, which was greater then than now. Continued melting and remelting added to the crust, and the final dregs of the crystallizing magma ocean, richer in those elements that do not easily fit into common crystallizing minerals (feldspar, pyroxene, and olivine), also ended up in the crust. The rocks from the dregs are commonly called "KREEP"-rich because they are richer in potassium (K), rare Earth elements (REE) such as lanthanum, and phosphorus (P) than are typical rocks. Most, though not all, of this crust was in place by 4.3 billion years ago.

At its birth and at about 3.9 billion years ago (what happened in the time between remains somewhat unknown) the Moon was subjected to enormous bombardments that created deep basins as well as numerous small craters, partly disrupting the crust. This crust is somewhat thinner on the front side (about 60 kilometers [37 miles]) than on the farside (about 100 kilometers [62 miles]).

The Younger Crust of the Moon

Impacts decreased substantially after 3.8 billion years ago, to a level close to that of today by about 3.2 billion years ago. The Moon's deep basins, partly filled with overlapping thin flows of mare basalt, formed from the melting of small amounts of the lunar interior. These basins (150 kilometers [93 miles] to perhaps 500 kilometers [310 miles] deep) are prominent as the dark plainsthe mariaof the Moon and show many signs of volcanic flow. Some of the volcanic lava erupted as fiery fountains, forming heaps of glass spherules . These lavas comprise only about 1 percent of the crust, but as the latest, topmost rocks, least affected by impacts, they remain clearly visible. They are much less abundant on the lunar farside, and everywhere their formation had ceased by 2 billion years ago. The Moon is now magmatically dead, and its uppermost crust is being continually gardened and converted into regolith.

The Origin of the Moon

Earth and the Moon show an identical relationship of oxygen isotope ratios (oxygen being the most common element in both planets), a relationship that is different from all other measured solar system objects (including Mars) except yEH chondrites. This indicates that Earth and the Moon formed in the same part of the solar system and gives credence to ideas that the Moon formed from Earth materials.

The pre-Apollo ideas of either capture, fission from Earth (by rapid spinning), or formation together as a double planet are not consistent with what scientists now know from geological or sample studies, nor with the orbital and angular momentum constraints. Thus a new concept was developed in the 1980s: Earth collided during its growth with an approximately Mars-sized object, producing an Earth-orbiting disk of material that accumulated to form the Moon. This idea can account for many features, including the chemistry of the Moon, its magma ocean, and even the tilt of Earth's axis. It is compatible with concepts of how planets develop by accumulation of solid objects. One of the implications of this theory is that the Moon actually must have accumulated very rapidly, on the order of days to years, rather than older ideas of tens of millions of years, and this explains the early melting of the Moon.

see also Apollo (volume 3); Apollo Lunar Landing Sites (volume 3); Exploration Programs (volume 2); Galilei, Galileo (volume 2); Lunar Bases (volume 4); Lunar Outposts (volume 3); Lunar Rovers (volume 3); Nasa (volume 3); Planetary Exploration, Future of (volume 2); Robotic Exploration of Space (volume 2); Shoemaker, Eugene (volume 2).

Graham Ryder

Bibliography

Heiken, Grant H., David Vaniman, Bevan M. French, and Jack Schmidt, eds. The Lunar Sourcebook: A User's Guide to the Moon. Cambridge, UK: Cambridge University Press, 1991.

Ryder, Graham. "Apollo's Gift: The Moon." Astronomy 22, no. 7 (1994):40-45.

Spudis, Paul D. "An Argument for Human Exploration of the Moon and Mars."American Scientist 80, no. 3 (1992):269-277.

. The Once and Future Moon. Washington, DC, and London: Smithsonian Institution Press, 1996.

. "The Moon." In The New Solar System, eds. J. Kelly Beatty, Carolyn C. Peterson, and Andrew Chaikin. Cambridge, UK: Cambridge University Press, 1999.

Taylor, G. Jeffrey. "The Scientific Legacy of Apollo." Scientific American 271, no. 1(1994):26-33.

Wilhelms, Donald E. To a Rocky Moon: A Geologist's History of Lunar Exploration. Tucson: University of Arizona Press, 1993.

National Aeronautics and Space Administration See NASA (Volume 3).

*The Galileo mission successfully used robots to explore the outer solar system. This mission used gravity assists from Venus and Earth to reach Jupiter, where it dropped a probe into the atmosphere and studied the planet for nearly seven years.

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moon

moon, natural satellite of a planet (see satellite, natural) or dwarf planet, in particular, the single natural satellite of the earth.

The Earth-Moon System

The moon is the earth's nearest neighbor in space. In addition to its proximity, the moon is also exceptional in that it is quite massive compared to the earth itself, the ratio of their masses being far larger than the similar ratios of other natural satellites to the planets they orbit (though that of Charon and the dwarf planet Pluto exceeds that of the moon and earth). For this reason, the earth-moon system is sometimes considered a double planet. It is the center of the earth-moon system, rather than the center of the earth itself, that describes an elliptical orbit around the sun in accordance with Kepler's laws. It is also more accurate to say that the earth and moon together revolve about their common center of mass, rather than saying that the moon revolves about the earth. This common center of mass lies beneath the earth's surface, about 3,000 mi (4800 km) from the earth's center.

The Lunar Month

The moon was studied, and its apparent motions through the sky recorded, beginning in ancient times. The Babylonians and the Maya, for example, had remarkably precise calendars for eclipses and other astronomical events. Astronomers now recognize different kinds of months, such as the synodic month of 29 days, 12 hr, 44 min, the period of the lunar phases, and the sidereal month of 27 days, 7 hr, 43 min, the period of lunar revolution around the earth.

The Lunar Orbit and Phases

As seen from above the earth's north pole, the moon moves in a counterclockwise direction with an average orbital speed of about 0.6 mi/sec (1 km/sec). Because the lunar orbit is elliptical, the distance between the earth and the moon varies periodically as the moon revolves in its orbit. At perigee, when the moon is nearest the earth, the distance is about 227,000 mi (365,000 km); at apogee, when the moon is farthest from the earth, the distance is about 254,000 mi (409,000 km). The average distance is about 240,000 mi (385,000 km), or about 60 times the radius of the earth itself. The plane of the moon's orbit is tilted, or inclined, at an angle of about 5° with respect to the ecliptic. The line dividing the bright and dark portions of the moon is called the terminator.

As the moon orbits the earth, the amount of its illuminated surface that can be seen from the earth changes. When none of the lighted half can be seen, because the moon is between the earth and sun, the moon is said to be new. For a few days before and after a new moon we can see a small part, or crescent, of the lighted half. When the moon has completed half its orbit from new moon to new moon, it is on the opposite side of the earth from the sun and we see the entire lighted half, or the full moon. When the moon has completed either one quarter or three quarters of its orbit from new moon to new moon, half the lighted side, the half-moon, is visible. The half-moon between the new and full moon is the first quarter and that between the full and new moon is the last quarter. Between a full moon and half-moon we see more than half the lighted side, or a gibbous moon. A blue moon is a second full moon in a calendar month; a black moon is a second new moon in a calendar month, or a calendar month with no full moon.

Retarded Lunar Motion

Due to the earth's rotation, the moon appears to rise in the east and set in the west, like all other heavenly bodies; however, the moon's own orbital motion carries it eastward against the stars. This apparent motion is much more rapid than the similar motion of the sun. Hence the moon appears to overtake the sun and rises on an average of 50 minutes later each night. There are many variations in this retardation according to latitude and time of year. In much of the Northern Hemisphere, at the autumnal equinox, the harvest moon occurs; moonrise and sunset nearly coincide for several days around full moon. The next succeeding full moon, called the hunter's moon, also shows this coincidence.

Solar and Lunar Eclipses

Although an optical illusion causes the moon to appear larger when it is near the horizon than when it is near the zenith, the true angular size of the moon's diameter is about 1/2°, which also happens to be the sun's apparent diameter. This coincidence makes possible total eclipses of the sun in which the solar disk is exactly covered by the disk of the moon. An eclipse of the moon occurs when the earth's shadow falls onto the moon, temporarily blocking the sunlight that causes the moon to shine. Eclipses can occur only when the moon, sun, and earth are arranged along a straight line—lunar eclipses at full moon and solar eclipses at new moon.

Tidal Influence of the Moon

The gravitational influence of the moon is chiefly responsible for the tides of the earth's oceans, the twice-daily rise and fall of sea level. The ocean tides are caused by the flow of water toward the two points on the earth's surface that are instantaneously directly beneath the moon and directly opposite the moon. Because of frictional drag, the earth's rotation carries the two tidal bulges slightly forward of the line connecting earth and moon. The resulting torque slows the earth's rotation while increasing the moon's orbital velocity. As a result, the day is getting longer and the moon is moving farther away from the earth. The moon also raises much smaller tides in the solid crust of the earth, deforming its shape. The tidal influence of the earth on the moon was responsible for making the moon's periods of rotation and revolution equal, so that the same side of the moon always faces earth.

Physical Characteristics

The study of the moon's surface increased with the invention of the telescope by Galileo in 1610 and culminated in 1969 when the first human actually set foot on the moon's surface. The physical characteristics and surface of the moon thus have been studied telescopically, photographically, and more recently by instruments carried by manned and unmanned spacecraft (see space probe and space exploration). The moon's diameter is about 2,160 mi (3,476 km) at the moon's equator, somewhat more than 1/4 the earth's diameter. The moon has about 1/81 the mass of the earth and is 3/5 as dense. On the moon's surface the force of gravitation is about 1/6 that on earth. It has been established that the moon completely lacks an atmosphere, but several space probes have found evidence of water ice in the soil. At its most extreme, the surface temperature can rise to above 125°C (257°F) at lunar noon at the equator and can sink below -245°C (-409°F) at night in the northern polar region. The gross surface features of the moon are visible to the unaided eye and were first studied telescopically in 1610 by Galileo.

Surface Features

The lunar surface is divided into the mountainous highlands and the large, generally roughly circular plains called maria (sing. mare; from Lat.,=sea) by early astronomers, who erroneously believed them to be bodies of water. The largest of the mare, Oceanus Procellarum or the Ocean of Storms, is rectangular in shape, however. The smooth floors of the maria, varying from flat to gently undulating, are covered by a thin layer of powdered rock that darkens them and accounts for the moon's low albedo (only 7% of the incident sunlight is reflected back, the rest being absorbed). The brighter regions on the moon are the mountainous highlands, where the terrain is rough and strewn with rocky rubble. The lunar mountain ranges, with heights up to 25,000 ft (7800 m), are comparable to the highest mountains on earth but in general are not very steep. The highlands are densely scarred by thousands of craters—shallow circular depressions, usually ringed by well-defined walls and often possessing a central peak. Craters range in diameter from a few feet to many miles, and in some regions there are so many that they overlap or several smaller craters lie within a large crater. Craters are also found on the maria, although there are nowhere near as many as in the lunar highlands. Other prominent surface features include the rilles and rays. Rilles are sinuous, canyonlike clefts found near the edges of mountain ranges. Rays are bright streaks radiating outward from certain craters, such as Tycho.

Mare and highland rocks differ in both appearance and chemical content. For example, mare rocks are richer in iron and poorer in aluminum than highland rocks. The maria consist largely of basalt, i.e., igneous rock formed from magma. In the highlands the majority of the rocks are breccias—conglomerates formed from basaltic rock and often studded with small, green, glassy spheres. These spheres probably were formed as the spray of molten rock, originally melted by the heat of meteorite impact, recongealed in midflight. The exposure ages of some rocks (the time their surfaces have been exposed to the action of cosmic rays that produce radioactive isotopes) are as short as 50 million years, much shorter than their crystallization ages. These rocks may have been shifted in position by meteorite impact or seismic activity (moonquakes). However, present lunar seismic activity is very low, corroborating the image of the moon as an essentially static, nonevolving world.

Internal Structure

Diffraction of seismic waves provided the first clear-cut evidence for a lunar crust, mantle, and core analogous to those of the earth. The lunar crust is about 45 mi (70 km) thick, making the moon a rigid solid to a greater depth than the earth. The inner core has a radius of about 600 mi (1,000 km), about 2/3 of the radius of the moon itself. The internal temperature decreases from 830°C (1,530°F) at the center to 170°C (340°F) near the surface. The heat traveling outward near the lunar surface is about half that of the earth but still twice that predicted by current theory. This heat flow is directly related to the rate of internal energy production, so that the internal temperature profile provides information about long-lived radio isotopes and the moon's thermal evolution. The heat-flow measurements indicate that the moon's radioactive content is higher than that of the earth. The moon's magnetic field is a million times weaker than that of the earth, but it varies by a factor of 20 from point to point on the surface. Certain rocks retain a high magnetization, indicating that they crystallized in the presence of magnetic fields much higher than those presently existing on the moon. Mascons are large concentrations of unusually high density that are located below certain of the maria. The mascons may have been created by the implantation of very dense, iron-rich meteorites, whose impact formed the overlying mare basins.

Formation and Evolution

It is now most commonly believed that moon formed when an object (sometimes called Theia after the mother of Selene, goddess of the moon) collided with the young earth. One theory holds that when a Mars-sized body impacted the earth the cores of the earth and object merged in the earth while material from the crust and mantle was blasted into orbit around the earth and later accreted to form the moon. Another theory holds that the body was larger and faster, delivering a glancing blow and contributing relatively little material to the earth-moon system that it created. After the moon's crust formed, subsequent impact of very large meteorites depressed the mare basins, at the same time thrusting up the surrounding crust to form the highlands. The mare basins later filled with lava flow, which in turn was covered by a thin layer of lunar "soil" —fine rock dust pulverized by the very slow mechanisms of lunar erosion (thermal cycling, solar wind, and micrometeorites). The craters were probably also formed by meteorite bombardment rather than by internal volcanic action as once believed. The rays surrounding the craters are material ejected during the impacts that formed the craters. The moon's rock types are correlated with its major geological periods.

Bibliography

See P. Moore and P. J. Cattermole, The Craters of the Moon (1967); D. Thomas, ed., Moon (1970); G. Gamow, The Moon (rev. ed. 1971); S. R. Taylor, Lunar Science (1975); B. M. French, The Moon Book (1977); W. K. Hartmann, ed., The Origins of the Moon (1986); B. Brunner, Moon: A Brief History (2010).

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Moon

Moon

The Moon is Earth's only natural satellite . Reflecting light from the Sun , the Moon is often the brightest object in the night sky.

The Moon orbits Earth at an average distance of approximately 240,000 miles (385,000 km). With revolution and rotation periods of approximately 27.32 Earth days, the Moon is in synchronous orbit about the earth. This synchronous orbit maintains a "near side" and "far side" of the Moon. The "near side" faces Earth, while the far side is not visible from Earth. Although Russian space probesand later many American probestook the first pictures of the far side of the Moon years earlier, it was not until the flight of Apollo 8 that United States astronauts became the first humans to directly view the far side of the Moon.

Orbital dynamics between the Sun, Moon, and Earth cause different patterns of illumination on the surface of the Moon as seen from Earth. As the Moon revolves about the earth, it appears to go through a series of illumination phases. The Sun constantly illuminates one-half of the lunar surface. The changing orientation in the three body system (Sun, Earth, and Moon), changes to what extent that solar illumination covers areas on the surface of the Moon that are visible from Earth.

Because the earth is revolving about the Sun, the displacement of the earth along it's orbital path establishes the time it takes to complete a cycle of lunar phasesa synodic monthand return the Sun, Earth, and Moon to the same starting alignment. This synodic month is approximately 29.5 days, and is longer than the 27.32-day sideral month.

A waxing moon is one where the area illuminated increases each night. A waning moon describes a decreasing area of illumination.

The Moon's phases are a cyclic repetition of illumination patterns described as: new moon, waxing crescent moon, waxing half moon, waxing gibbous moon, full moon, waning gibbous moon, waning half moon, waning crescent moon, followed by a return to the new moon phase.

A new moon occurs when the Moon's orbital path places it between the earth and the Sun. Only the side of the Moon not visible to Earth is illuminated and the Moon is lost in the bright sunlight. Occasionally when the Moon is also in the proper plane of alignment, it may provide a full or partial solar eclipse over portions of Earth's surface.

Relative to the Sun and starfield, the Moon appears to move eastward. Following the new moon, the next night, a small sliver or crescent becomes illuminated. The waxing crescent moon is low on the western horizon and is visible just after sunset (i.e., the Moon "sets" shortly after sunset). As the orbital dynamics shift, the crescent grows largerand the Moon sets latereach night following sunset. Approximately one week following the new moon, the Moon is one quarter of the way through it's orbital revolution of Earth, and one half of the lunar surface is illuminated as a waxing half moon. Depending upon latitude , the waxing half moon appears nearly directly overhead (at the zenith of the celestial meridian) at sunset. The waxing half moon will set about midnight local time. During the next week, the area of the Moon reflecting sunlight to Earth covers more than half of the visible lunar surface, and is described as a waxing gibbous moon.

Approximately two weeks after the new moon, the visible surface of the Moon becomes fully illuminated because the Moon is on the opposite side of Earth relative to the Sun. If the earth and Moon are in the proper plane, Earth may actually block the Sun's light over a portion of the lunar surface and cause a partial to full lunar eclipse. The full moon rises at sunset and sets at dawn.

Following the full moon, the Moon begin to progressively darken through waning gibbous phases until about a week following the full moon it forms a waning half moon. The waning half moon rises about midnight and sets about noon the next day. Continued darkening over the last week of the lunar cycle provides a waning crescent moon that finally returns full cycle to the new moon state, where the Moon and Sun, on the same side of Earth's orbit about the Sun, appear to rise and set together.

The phases of the Moon proved one of the most fundamental astronomical calendars for ancient peoples and the ancient Greek astronomers asserted that the Moon reflected the Sun's light. Phases of the Moon remain critical in determining the date and timing of many religious observances (e.g., Passover, Easter, Ramadan, Visakha Puja, etc.)

Because the earth is larger than the Moon and relatively close to the Moon, it casts a large shadow that causes lunar eclipses. Solar eclipses (where the Moon blocks the Sun) are less frequent and are only possible because, although the Sun is much larger than the Moon, the Moon is much closer to Earth. The present set of orbital dynamics and distances allow solar eclipses because the Sun and Moon have the same angular size (approximately 0.5°) when viewed from Earth. The average human thumb, held out at arm's length obscures approximately 0.5° degrees and will thus, block both the Sun and Moon. (Warning: Direct viewing of the Sun may cause blindness or optic injury and should not be attempted. Solar observation requires special protective goggles that filter and reduce the intensity of sunlight. )

The Moon appears to shift its position eastward on the celestial sphere by approximately 13° per night (i.e., appears to move 13° to the east from its prior position if observed at the same time on successive nights).

The Moon is nearly spherical with polar and equatorial radii varying by about a mile. The equatorial radius of the Moon is approximately 1,080 miles (1,738 km). The diurnal temperatures (the day/night temperatures) on the Moon range from approximately 280°F to +260°F (173°C to +126°C). Contrary to popular belief, the Moon does have a thin atmosphere that consists of helium, argon, methane, minute amounts of oxygen , and other trace elements. The density of the lunar atmosphere is only approximately 2 × 105 particles/cm3 and results in a lunar atmospheric pressure of only 8.86 × 1014 inHg (3 × 1012 mb) in contrast to Earth's average surface atmospheric pressure of 29.92 inHg (1,014 mb).

The thin and dry lunar atmosphere provides no substantial weathering agents (e.g., wind, water , etc.) and so erosional processes are greatly slowedessentially reduced to heating, cooling, and slow geochemical changes. The thin atmosphere also offers no protection from meteor impacts and the combination of lack of protection and lack of Earth-like erosion produces a heavily cratered lunar landscape that preserves billions of years of accumulated impact craters.

Although the Moon is a quarter of Earth's size, it has only approximately 1.2% of Earth's mass. The gravitational attraction at the surface of the Moon is about one-sixth that of the gravitational attraction at Earth's surface. Accordingly, neglecting air friction (something easily accomplished on the Moon but not on Earth) an object in freefall near Earth's surface accelerates at 9.8 m/s2, but near the lunar surface, the acceleration due to gravity is approximately 1.62 m/s2.

See also Celestial sphere: The apparent movements of the Sun, Moon, planets, and stars; Diurnal cycles; Earth (planet); History of manned space exploration; Gravity and the gravitational field; Solar system

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Moon

Moon

The Moon is a roughly spherical, rocky body orbiting Earth at an average distance of 240,00 miles (385,000 kilometers). It measures about 2,160 miles (3,475 kilometers) across, a little over one-quarter of Earth's diameter. Earth and the Moon are the closest in size of any known planet and its satellite, with the possible exception of Pluto and its moon Charon.

The Moon is covered with rocks, boulders, craters, and a layer of charcoal-colored soil from 5 to 20 feet (1.5 to 6 meters) deep. The soil consists of rock fragments, pulverized rock, and tiny pieces of glass. Two types of rock are found on the Moon: basalt, which is hardened lava; and breccia, which is soil and rock fragments that have melted together.

Elements found in Moon rocks include aluminum, calcium, iron, magnesium, titanium, potassium, and phosphorus. In contrast with Earth, which has a core rich in iron and other metals, the Moon appears to contain very little metal. The apparent lack of organic compounds rules out the possibility that there is, or ever was, life on the Moon.

The Moon has no weather, no wind or rain, and no air. As a result, it has no protection from the Sun's rays or meteorites and no ability to retain heat. Temperatures on the Moon have been recorded in the range of 280°F (138°C) to 148°F (100°C).

Formation of the Moon

Both Earth and the Moon are about 4.6 billion years old, a fact that has led to many theories about their common origin. Before the 1970s, scientists held to one of three competing theories about the origin of the Moon: the fission theory, the simultaneous creation theory, and the capture theory.

The fission theory stated that the Moon spun off from Earth early in its history. The Pacific basin was the scar left by the tearing away of the Moon. The simultaneous creation theory stated that the Moon and Earth formed at the same time from the same planetary building blocks that were floating in space billions of years ago. The capture theory stated that the Moon was created somewhere else in the solar system and captured by Earth's gravitational field as it wandered too close to the planet.

After scientists examined the age and composition of lunar rocks brought back by Apollo astronauts, they discarded these previous theories and accepted a new one: the giant impact theory (also called the Big Whack model). This theory states that when Earth was newly formed, it was sideswiped by a celestial object that was at least as massive as Mars. (Some scientists contend the object was two to three times the mass of Mars.) The collision spewed a ring of crustal matter into space. While in orbit around Earth, that matter gradually combined to form the Moon.

The evolution of the Moon has been completely different from that of Earth. For about the first 700 million years of the Moon's existence, it was struck by great numbers of meteorites. They blasted out craters of all sizes. The sheer impact of so many meteorites caused the Moon's crust to melt. Eventually, as the crust cooled, lava from the interior surfaced and filled in cracks and some crater basins. These filled-in basins are the dark spots we see when we look at the Moon.

To early astronomers, these dark regions appeared to be bodies of liquid. In 1609, Italian astronomer Galileo Galilei became the first person to observe the Moon through a telescope. He named these dark patches "maria," Latin for "seas."

In 1645, Polish astronomer Johannes Hevelius, known as the father of lunar topography, charted 250 craters and other formations on the Moon. Many of these were later named for philosophers and scientists, such as Danish astronomer Tycho Brahe, Polish astronomer Nicolaus Copernicus, German astronomer Johannes Kepler, and Greek philosopher Plato.

Humans on the Moon

All Earth-based study of the Moon has been limited by one factor: only one side of the Moon ever faces Earth. The reason is that the Moon's rotational period is equal to the time it takes the Moon to complete one orbit around Earth. It wasn't until 1959, when the former Soviet Union's space probe Luna 3 traveled to the far side of the Moon that scientists were able to see the other half for the first time.

Then in 1966, the Soviet Luna 9 became the first object from Earth to land on the Moon. It took television footage showing that lunar dust, which scientists had anticipated finding, did not exist. The fear of encountering thick layers of dust was one reason both the Soviet Union and the United States hesitated sending a man to the moon.

Just three years later, on July 20, 1969, U.S. astronauts Neil Armstrong and Edwin "Buzz" Aldrin aboard Apollo 11 became the first humans to walk on the Moon. They collected rock and soil samples, from which scientists learned the Moon's elemental composition. There were five more lunar landings in the Apollo program between 1969 and 1972. To this day, the Moon remains the only celestial body to be visited by humans.

Water on the Moon?

In late 1996, scientists announced the possibility that water ice existed on the Moon. Clementine, a U.S. Defense Department spacecraft, had been launched in January 1994 and orbited the Moon for four months. It surveyed a huge depression in the south polar region called the South Pole-Aitken basin. Nearly four billion years ago, a massive asteroid had gouged out the basin. It stretches 1,500 miles (2,415 kilometers) and in places is as deep as 8 miles (13 kilometers), deeper than Mount Everest is high.

Areas of this basin are never exposed to sunlight, and temperatures there are estimated to be as low as 387°F (233°C). While scanning these vast areas with radar signals, Clementine discovered what appeared to be ice crystals mixed with dirt. Scientists speculated that the crystals made up no more the 10 percent of the material in the region. They believe the ice is the residue of moisture from comets that struck the Moon over the last three billion years.

To learn more about the Moon and this possible ice, the National Aeronautics and Space Administration (NASA) launched the Lunar Prospector in January 1998. This was NASA's first mission back to the Moon in 25 years. As the name of this small, unmanned spacecraft implied, its nineteen-month mission was to "prospect" the surface composition of the Moon, providing a detailed map of minerals, water ice, and certain gases. It also took measurements of magnetic and gravity fields, and tried to provide scientists with information regarding the size and content of the Moon's core. For almost a year, Lunar Prospector orbited the Moon at an altitude

of 62 miles (100 kilometers). Then, in December 1998, NASA lowered its orbit to an altitude of 25 miles (40 kilometers). On July 31, 1999, in a controlled crash, the spacecraft settled into a crater near the south pole of the Moon. If there were water at the crash site, the spacecraft's impact would have thrown up a huge plume of water vapor that could have been seen by spectroscopes at the Keck Observatory on Mauna Kea, Hawaii, and other telescopes like the orbiting Hubble Space Telescope. However, no such plume was observed. For scientists, the question of whether there is hidden ice on the Moon, delivered by impacting comets, is still open. It is estimated that each pole on the Moon may contain up to 1 billion tons (900 million metric tons) of frozen water ice spread throughout the soil.

[See also Orbit; Satellite; Spacecraft, manned ]

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moon

moon Natural satellite of a planet; in particular the natural satellite of the planet Earth. Apart from the Sun it is the brightest object in the sky as seen from the Earth, being at a mean distance of only 384,000km (239,000mi). Its diameter is 3476km (2160mi). As the Moon orbits the Earth, it goes through a sequence of phases. Its surface features may be broadly divided into the darker maria, which are low-lying volcanic plains, and the brighter highland regions (sometimes called terrae), which are found predominantly in the s part of the Moon's near side and over the entire far side. The origin of the Moon is uncertain. A current theory is that a Mars-sized body collided with the newly formed Earth, and debris from the impact formed the Moon. On July 20, 1969, Neil Armstrong became the first person to walk on the Moon. The chemical composition of material from the Moon consisted mainly of silica, iron oxide, aluminium oxide, calcium oxide, titanium dioxide, and magnesium oxide. Lunar rocks are igneous rocks. The Moon has only the most tenuous of atmospheres; Apollo instruments detected traces of gases, such as helium, neon and argon. The surface temperature variation is extreme, from 100 to 400K. In 1998, a probe discovered water-ice near the Moon's poles.

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moon

moon / moōn/ • n. (also Moon) the natural satellite of the earth, visible (chiefly at night) by reflected light from the sun. ∎  a natural satellite of any planet. ∎  (the moon) fig. anything that one could desire: you must know he'd give any of us the moon. ∎  a month, esp. a lunar month: many moons had passed since he brought a prospective investor home. • v. 1. [intr.] behave or move in a listless and aimless manner: lying in bed eating candy, mooning around. ∎  act in a dreamily infatuated manner: Timothy's mooning over her like a schoolboy. 2. [tr.] inf. expose one's buttocks to (someone) in order to insult or amuse them: Dan had whipped around, bent over, and mooned the crowd. PHRASES: many moons ago inf. a long time ago. over the moon inf. extremely happy; delighted. DERIVATIVES: moon·less adj. moon·like / -ˌlīk/ adj.

phases of the moon

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Moon

280. Moon

See also 25. ASTRONOMY ; 318. PLANETS ; 387. SUN .

selenography
the branch of astronomy that deals with the charting of the moons surface. selenographer, selenographist , n. selenographic, selenographical , adj.
selenolatry
the worship of the moon.
selenology
the branch of astronomy that studies the physical characteristics of the moon. selenologist , n. selenological , adj.
selenomancy
a form of divination involving observation of the moon.

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Moon

Moon The Earth's satellite, with a mass 1/81 that of the Earth, density 3344 kg/m3, and radius 1738 km. The average Moon—Earth distance is 384500 km. The Moon has no atmosphere and surface temperature extremes range from 127 to –173 °C. A feldspathic lunar highland crust 60–120 km thick overlies a silicate mantle. Basaltic lavas cover 17% of the surface. There is probably a small iron core of 300–400 km radius (2–3% of lunar volume).

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Moon

MOON

MOON . To observers on earth, the moon appears to be the most changeable of celestial phenomena. In earlier times the appearance of the new crescent was often greeted with joy as a return of the moon from the dead; the full moon was considered an occasion for celebration, the waning a time of anxiety, and the eclipse a cause for dread. In religion and mythology the moon plays a variety of roles. It is personified as a male or female divinity, or, like the sun, thought to be an object thrown up into the sky by some supernatural being. It may be thought of as kindly or malicious, male or female, pursued or pursuer, a god of destruction or of birth and growth.

An early recognition of a connection with menstruation gave rise to the conception of the moon as the guardian of the female cycle and of birth or, alternatively, as a male god who monthly defiles women. In connection with dew, rain, or tides, the moon may promote the growth of vegetation or bring disastrous floods.

The moon has been a measure of time from early times, especially for hunting societies. In tropical climates, where the sun is cruel, the moon is considered beneficent, especially by nomads and caravan drivers. As a male god the moon appears as the Strong Bull of Heaven who cares for his cows, the stars; or as the sacrificed god, the son or lover of the mother goddess.

As a goddess, the moon brings cures and eases childbirth or, on the other hand, helps to rot corpses and receives the dead. The waxing and waning of the moon led to the idea that it dies and is reborn, and thus the moon became a part of funeral ceremonies and rites of resurrection. The discovery that the moon is the closest celestial body to the earth led to the idea that the moon was the "abode of souls," a way station to immortality.

The phases of the moon seem to echo the life cycles of women and therefore connect the moon with the Triple Goddess who presided over birth, initiation, and death. The Moon became part of a triad with Hekate, goddess of the underworld, and with Artemis, the divine huntress, whose hounds were the stars. Sometimes even the Egyptian goddess Isis joined the grouping. In this connection the qualities of the moon are fertility, moisture, change, darkness, and magic. In the ancient Chinese division of the universe into yang (hot, dry, strong, male) and yin (cool, moist, weak, female) the moon is considered yin.

Usually the waxing moon is a fortunate omen and waning moon a dangerous one. In the Andaman Islands the waxing moon is male and the waning moon female. The dark of the moon is the time for gathering herbs to be used in spells and curses. The new or full moon is the time for white magic. In some systems, however, the moon rushes to conjunction with the sun to be refreshed by his light.

In poetry, the dying god, who is related to the divine powers of the plant world, is often compared to the moon. Intoxicating liquors used in many religious ceremonies are said to drip forth from the moon. As spider, spinner, and weaver, the moon is likened to the three Fates, who spin and weave man's destiny.

The moon is often paired with the sun, as either father, son, wife, sister, or daughter. Sometimes the moon and sun are twins, and the weaker one, usually the moon, is doomed to live in the underworld, while the other rides on high. Frequently both are thought of as boats riding through the ether as on the ocean. Often, the sun rides in a chariot pulled by four white horses. The moon is pulled by two white horses, or by a bull, a stag, or a cock.

The moon's animal is often the bull, because of the crescent shape formed by its horns, or the hare, because of its fertility or because the "man in the moon" is thought to resemble a hare. The bear is also associated with the moon, because its hibernation and waking are like death and resurrection; the snail, because it retreats and reappears; or the frog, because it is an aquatic creature.

The Moon as a Measure of Time

Aside from night and day, the moon is the most obvious natural measure of time. The Indo-European root is the same for the moon, month, and measure. There exist what may be notations of the moon's phases in Paleolithic caves in Spain from 7000 bce. Stonehenge in Great Britain (c. 3000 bce) may have been used to measure the movements of the moon as well as those of the sun. There are still primitive peoples who use only the moon to measure time. Before the arrival of Europeans, American Indians counted the lunations as "war month," "month of flowers," and so forth. The dark of the moon was the "naked time"; its first appearance, the "coming to life."

Agricultural people, however, needed to have their times of planting and reaping coincide with the seasonsthat is, with the sun. Thus began the long effort to correlate twelve lunations (too few) or thirteen lunations (too many) with the solar year. Accounts from republican Rome show the problems associated with this effort. We are told that from earliest times a pontifex minor would watch for the new moon from the Capitoline Hill, and when it was sighted, call out to Juno, the queen of the gods. The first of the month was called the calends from the verb "to call out." Juno is in this way identified with the new moon, as her husband, Jupiter, is with the ides, or full moon. The priest then announced the series of festivals for the coming month and whether the nones (the half-moon) would fall on the fifth or the seventh. The festivals, sponsored by the state, were instituted as a means of keeping the agricultural, military, and civil activities in order. It was necessary for all farmers to come into the city to learn on what days they could not work but must keep festival. On calendars that have come down to us, festival days are marked nefas, meaning that no work could be done; 109 out of the 355 days of the year were designated nefas.

The priesthoods, like the early magistracies, were in the hands of the patricians. The inconvenience of not knowing the feast days was one of the problems that led to the "struggle of the orders." Eventually the fasti (calendars) were published, in 304 bce. The year began in March, and any time that had to be intercalated to bring the months into line with the seasons was added in February, after the Terminalia (a festival of boundaries and the year's end, celebrated on February 23).

Until the end of the republic the work of intercalation was the duty of the pontifices, who were often inefficient or corrupt. For instance, the date of court cases could be shifted by altering the intercalations. By the end of the republic, the whole calendar was out of harmony with both the sun and the moon. Cicero, writing to his friend Atticus, says he is not sure whether or not there will be an intercalation. There was a clause in contracts that read "si intercalat" ("in case of an intercalation").

Julius Caesar, aided by his Egyptian astronomer, made a clean sweep of the quasi-lunar calendar, extended the year 45 bce from 355 to 445 days, and started anew on January 1, 45 bce, with a cycle of 365 days, adding another day on the fourth year, after the Terminalia. This, with a few adjustments, is the solar calendar under which we live.

The ancient Greeks sent out criers to announce the sighting of the new moon. At some unknown point in history, the Greeks had limited the length of the year to twelve lunations of "full" or "hollow" months (comprised of thirty and twenty-nine days respectively), with an intercalary month every two years. We learn from Geminus that "they sought for a period which should, as to years agree with the Sun, as to months, with the Moon." The first period they constructed was an eight-year cycle called the octaeteris.

A nineteen-year cycle was suggested by the astronomer Meton in 432 bce but was apparently not accepted by the cities, which went their own way, creating their own calendars and even inventing their own names for the months. In The Clouds of Aristophanes, the Moon complains, "You subvert the calendar and fail to observe her days. When the sacred days are unobserved, the gods go hungry, and it is the Moon they threaten." In this confusion, many citizens returned to direct personal observation of the rising moon. Beginning in the second century bce, two sets of dates were recorded, "according to the state and according to the deity [Selene]."

In Mesopotamia the month began with the sighting of the new moon. A letter to the Assyrian king Esarhaddon (r. 680669 bce) states, "On the thirtieth I saw the moon. It was in a high position. The king should wait for the report from the city of Assur and then may determine the first day of the month." There are indications that in some cities months alternated between thirty and twenty-nine days in a nineteen-year cycle with regular intercalations. By the time of the Seleucids (third century bce), it was possible to calculate the appearance of the new moon and to predict eclipses.

In India, religious festivals are still regulated by the lunar calendar, as are such domestic events as marriages. The moon festivalstwo days for the new moon, one for the full moonare considered important, even by Buddhists. The present names of the months are derived from the nakshatras ("lunar mansions"), twenty-seven or twenty-eight conspicuous stars along the ecliptic through which the moon passes.

The early Hebrews celebrated the new moon with a feast, which was a family gathering at which animals were sacrificed. The months were identified by the agricultural activity taking place at the time. The beginning of the month, after being attested to by observers, was announced to various communities by fire signals at first, and later by messengers. Since messengers could not always reach the outlying groups in a day, festivals often went on for two days. Since Passover, celebrated at the full moon, was originally a feast of the first fruits, it had to occur after the reaping of the grain. Thus it became necessary to add another month after Adar (approximately March). After the exile the calendar followed the Babylonian system, using Babylonian names for the months, counting the days from the evening, and intercalating an extra month on a regular basis. After the third century there was increasing dependence on calculation of the beginning of the month, though some sects from time to time insisted on reverting to direct observation.

The lunar year to which Muslims adhere was not established until 631 ce, when Muhammad made his last pilgrimage to Mecca. There he proclaimed that the year should consist of twelve lunar months and that intercalation should be forbidden. As Arabs before that time had probably had a combination lunar and solar calendar, it is likely that Muhammad intended to discourage old pagan festivals. His system won acceptance by the Arabs, who since ancient times held the moon in special reverence. The festivals now run through the whole year and come back to the same solar season in about thirty-three years. The new month begins when two trustworthy Muslims notify the authorities that they have observed the new moon from a mountaintop or from an open field. The crescent motif (the hilal) has been much used throughout the centuries in Islamic art and in the last two hundred years has appeared on the standard of Islam.

Early Christians attached importance to celebrating Easter at the time of the Jewish Passover but agreed that Easter should fall on a Sunday. In the third century Christians began to frame lunar calculations for themselves. The Easter controversy raged in the early church and still exists between the Western and Eastern churches. The final conditions arrived at in the West are that Easter must be kept on the Sunday after the paschal moon (the calendar moon whose fourteenth day falls on or after the vernal equinox), reckoned from the day of the new moon inclusive.

The Moon as Deity

Only once, so far as is known, did the moon as divinity command political power and an influential priesthood, but it did so for about three thousand years, through changes of race, language, and regime. The place was the area between the Tigris and Euphrates rivers, known as Mesopotamia ("between the rivers"), and the cult spread or grew independently in Syria, Palestine, Arabia, and Anatolia.

In the southern part of the Land between the Rivers there appeared around 5000 bce the first urban civilizationa group of cities in which trade, division of labor, metalworking, organized religion, and writing were developed by a people whom history knows as Sumerians. Each of the cities was under the protection of a high god and in the beginning was probably ruled by the priesthood of the god. By the time the first records appear, these gods are all related. An is the creator-sky god. His son, Enlil, the Air, carries on most of the business of controlling the other gods and resides in the holy city of Nippur. The first son of Enlil is Nanna, the Moon, patron of the important city of Ur. His wife is Ningal, daughter of the Lady of the Reeds, a moisture goddess from the marshes. The children of Enlil and Ningal are Utu, the Sun, and Inanna, warrior goddess of love and the Evening Star. The trio of Moon, Sun, and Evening Star are often found together on royal stelae down through Babylonian times.

The Semitic-speaking peoples who succeeded the SumeriansAkkadians, Assyrians, and Babylonianstook over most of their inventions and adopted the Sumerian pantheon, giving the gods Semitic names. Nanna became Sin; Utu, Shamash; and Inanna, Ishtar.

C. Leonard Woolley, excavating at Ur in 19221934, found the famous royal tombs, containing the bodies of mass suicides, royal ladies (who Woolley surmised might have been priestesses of the Moon), and a harp with a bull's head and a lapis lazuli beard, the Strong Bull of Nanna. He also describes the ziggurat of Ur, dedicated to the Moon, the best preserved of its kind in the Near East. At the top of the ziggurat, a high staged tower terraced with trees, was a shrine where the god rested, gave dream oracles, or took part in a sacred marriage. This last is suggested by a hymn in which Ningal addresses Nanna, "In your house on high I will come to you, Nanna. In your perfumed cedar mountain, in your mansion of Ur, I will come to live."

At the base of the ziggurat was a large temple, the real home of the god, where he was fed and clothed daily. Probably the people saw the god only when he was paraded at each phase of the moonon the first, seventh, and fifteenth days of the month. The temple was a huge complex of storehouses, kitchens, and rooms for priests and slaves. It was a landowner and received rent in kind, which was used for sacrifices and for feeding the enormous staff. Slaves were employed in smelting, weaving, and preparing goods for sale. The high priestess of Nanna was traditionally a king's daughter.

A text describes how Nanna made a pilgrimage to visit his father Enlil at the holy city of Nippur, taking agricultural products and receiving in return Enlil's blessing. Enlil confirmed his son in power as Nanna, the king of Ur. It is likely that the king acted out the life of the god. During the dark days of the moon, called the "days of lying down," the queen conducted the rituals.

The temple complex at Ur was destroyed and reconstructed many times over the centuries, by Assyrians, Babylonians, even by alien Kassites, and finally by Cyrus, the Persian invader. The complex was rebuilt not to conciliate the people but to preserve good relations with the god.

The Assyrians, who took over from the Sumerians the worship of the moon under the name of Sin, built another moon city, Haran, on the Euphrates. The Assyrian kings came to Haran to "take the hand" of Sin after they had been confirmed by their own god, Ashur. In the sanctuary at Haran was a dream oracle, where Esarhaddon (r. 680669 bce) was told to proceed to the conquest of Egypt, which he did. Moon worship continued at Haran well into Islamic times when it was the center for a planet-worshiping people called the Sabaeans. The emperor Julian worshiped the moon at the temple in Haran in 365 ce.

In the early sixth century bce, Babylon was the area's greatest city. Its founder, Nebuchadrezzar, set about rebuilding Ur. His successor, Nabonidus, was an antiquarian and a devoted worshiper of the moon. His mother (or grandmother) had been governor of Haran, and he was perhaps partly of West Semitic origin. In records of Ur, Nabonidus found the inscription of Ur-Namma, founder of the third dynasty of Ur (2100 bce), whom he called "a king before me." Upon the ancient foundation he rebuilt the ziggurat "as in old times." He also rebuilt the temple at Haran and one in the Arabian city of Tema, where he remained for eleven years. Many critics in Babylon claimed he was putting his god Sin above Marduk.

The name of the moon in Canaan was Yarih. A Canaanite text tells of his wedding to Nikkal (related to Ningal, wife of the Sumerian moon god): "I shall make her field into vineyards, the field of their love an orchard" (Samuel Noah Kramer, Ugaritic Manual, 1955, no. 77). There is no doubt that the golden calf worshiped in Genesis was a figure of the moon and that Mount Sinai was his home.

Throughout Anatolia there are depictions of and inscriptions to the Anatolian moon god, called Men, from the Indo-European root for moon and measure. He was known as Menotyrannus ("lord of the moon"), Men Ouranios ("lord of the sky"), or Katachonios ("lord of the underworld"), suggesting that he was a god of death and rebirth. We cannot be sure whether he arrived along the trade routes from the Near East or was an indigenous deity. Later Men became confused with the "dying and rising god" Attis, the castrated follower, son, or lover of the Great Mother of Phrygia, Cybele, as well as with Dionysos and Sabazios of Thrace, two other dying and rising gods.

The Moon in Mythology

In ancient India, Soma was the deification of a sacred plant that, when pressed, strained, and mixed with milk and barley, became an intoxicating drink for men and gods. The whole ninth book of the gveda is devoted to the praise of the yellow drink, which it identifies with the yellow moon. There is a marriage hymn in which the god Soma is married to the Sun, Sūrya, and has his head in the laps of the Nakatras ("lunar mansions"). Soma is celestial and bright, dispelling darkness and dwelling in the waters. In a later hymn, Soma is said to have married all twenty-seven Nakatras, daughters of the creator god, but he prefers one, Rohiī (possibly identified with the evening star). The other wives complain to their father, who afflicts the moon with a wasting sickness, causing his waning and disappearance. The Moon promises to reform and then grows back again, but always he relapses. In this problem the Moon is aided by Śiva, like Soma an ancient god of change, fertility, and destruction. Śiva wears the Moon's crest on his head; Soma is known as the "crest of Śiva." In a wheeled chariot drawn by a horse or an antelope, Soma leaves the sky to visit the earth at the new moon to revitalize plants and animals. Soma as an intoxicating drink has been compared to the wine of the Greek Dionysos, which the playwright Euripides described as "a drink that is poured out, a god for a god."

In Iran there is also a ritual of the sacred drink, there called haoma, which is not identified with the moon. In one hymn, the Moon is one of a triad of divinities, the lowest one being the sacred ox, who is sacrificed. The seed of the ox enters the Moon, where it is purified and divides into all the species of plants and animals. Iranians dedicated the right eye of every sacrificed animal to the Moon. They believed that when all things were put in motion by Angra Mainyu, or Evil, the Moon created time, which will run until Angra Mainyu is overthrown.

The ancient Greeks had only one myth concerning the moon, there called Selene, "the bright one." It is the story of how she fell in love with Endymion, a prince of Elis, while he was sleeping on Mount Latmos in Asia Minor. She begged Zeus to give Endymion eternal sleep so that she could visit him every night. In this way she managed to have fifty children by him, the number of the lunations between Olympic games, or equal to one-half of the eight-year cycle. Though there are almost no rituals associated with the moon in Greece, there are traces of moon worship from earlier times and in outlying regions. The Endymion myth connects Asia Minor with western Greece. According to Plato, mothers and nurses in ancient times taught children to bow down to the new moon. Torchlight parades for Selene are mentioned. A dream oracle in the Peloponnese, frequented by ephors from Sparta, was dedicated to Helios (the Sun) and to Pasiphae (the name, meaning "shining on all," is an epithet of the Moon). There was a queen named Pasiphae in Crete, where there are many traces of bull worship. In the myth, this Pasiphae fell in love with a white bull and from their union produced the Minotaur, who was half man and half bull. Another bull brought Europa (whose name, meaning "broad-faced," is another epithet for the Moon) from Phoenicia to Crete.

In Baltic mythology the sun is feminine and the moon masculine. The Balts say that the Sun was once married to the Moon, but he left her for the Morning Star. This so enraged the storm god, the most important Baltic god, that he beat the Moon with his sword, thus reducing the latter's size. The Sun and Moon have many children, the stars, but the Morning Star is a product of a union of the Sun with the storm god himself. The Moon, in shame and anger, avoids his wife, and they never appear together.

In Japan, the Sun, the most important divinity, is feminine; the Moon, her brother, plays only a minor role. Once the Sun ordered the Moon to go down to earth to find out what the goddess of food was doing. When the Moon arrived on earth, the goddess of food, meaning to please him, turned her face toward the land and from her mouth poured out boiled rice; toward the sea, all kinds of fish; and toward the mountains, all kinds of game. The Moon, instead of being pleased, was so enraged that she had offered him things from her mouth that he killed her. Out of her corpse were born the horse, the cow, and the silkworm. Back in Heaven the Sun, angry with her brother for what he had done, said, "I'll see you no more," and so they never meet.

Another myth of plant discovery is told by the Machiganga of Peru. It relates that the Moon gave mortals cultivated plants, giving instructions about them to a mortal girl whom he eventually married. He caused his wife to be fertilized by a fish, and she produced four sons: the daytime Sun, the planet Venus, the Sun Under the Earth (i.e., the sun at night), and the nocturnal Sun, invisible to all but shedding its light on the stars. This fourth child was so hot that he scorched his mother's womb, and she died. The Moon's mother-in-law reproached him, saying that there was nothing left for him to do but to eat the corpse. His wife, disgusted with life on earth, had left her body there and taken her soul to the underworld. The Moon was distressed but obeyed his mother-in-law. Thus the Moon became an eater of corpses and decided to move far away from the earth.

All types of creation myths explain the origin of the moon, usually together with the sun. The cosmic egg motif occurs in the Finnish epic Kalevala: the egg falls from heaven onto the knee of the creator goddess as she floats in the cosmic waters, and from it emerge all the aspects of the universe. The sun was made out of the yellow of the egg and the moon out of the white. In Greenland, the Sun and Moon are a mortal pair, sister and brother. In a house with no light they lay together. When the sister discovered that she had committed incest, she tore off her breasts and threw them at her brother; the holes they left became sunspots. Then she flew away and he after her, both carrying torches. The sister's torch burned brighter so she became the sun, and her brother, the moon.

To the type of myth in which the world is created out of the body of a primal being belongs the Huron story of Ataentsic. She was a creation mother goddess who was thrown down from heaven through the hole in the sky she had made by tearing up the world tree. Landing on earth, she gave birth to twins, one good and one evil. The evil son killed her, but the good one made the sun from her face and the moon from her breasts.

In the Aztec pantheon, Huitzilopochtli is a warrior god, culture hero, and the sun. When Mother Earth became pregnant with him (her last child), her other children, the stars, were angry and pursued her to kill her. But one, called Golden Bells, ran ahead to warn her mother. The sun god sprang fully armed from the womb and beheaded Golden Bells. Learning that she had meant well, in compensation he put her head in the sky as the moon, but he chased the other stars away, as the sun does at rising.

The Greek Hesiod (seventh century bce) describes all creation as the result of sexual union. From the original parents, Earth and Sky, were born twelve Titans, who paired off and produced most of the natural objects as well as the gods. One pair, Theia and Hyperion, become the parents of the Sun (Helios), the Moon (Selene), and the Dawn (Eos). Another pair of Titans became the grandparents of Hekate, goddess of the underworld, and of Artemis, the huntress. Hekate and Artemis later became identified with the moon. In the Homeric Hymn to the Moon (sixth century bce), the Moon has a daughter, Pandia, by Zeus. There was a festival at Athens called the Pandia where round moon cakes were sold and eaten.

In one of the emergence myths characteristic of the southwestern United States, the Pueblo tell how mortals came up in several stages to the surface of the earth. Finding it in darkness, they tossed into the sky the moon and sun, which they had brought with them. A variant of the emergence myth is found in Oceania, in which mankind or the gods are originally enclosed in a shell that they have to pry open. In a Micronesian story, the creator god, Ancient Spider, encased in such a shell, found two snails; after he opened the shell he used the smaller for the moon and the larger for the sun.

In Queensland, the Sun is a woman made by the Moon; although she has two legs, she has a number of arms, which can be seen as the sun's rays. Among the Aranda (Arunta) of Australia, a man of the Opossum totem carried the Moon around with him in a shield, keeping it hidden in a cleft of the rocks all day. One day a man of another totem saw the Moon shining and ran away with it. The Opossum man, unable to catch the thief, called out to the Moon to rise into the sky and shed light on everyone. This it did, and it has remained in the sky ever since.

According to the Pima Indians of North America, the Sun and Moon are parents of Coyote, the famous trickster figure in mythology. In another story, it is Coyote who invents the Sun and Moon. Some Altaic-speaking peoples of Siberia believe that in the beginning there was no sun or moon, but people themselves flew around in the air and gave out light. A high god sent a spirit to help them. Stirring the primeval waters, he found two mirrors, which he set up in the sky as the sun and the moon. Mirrors are often used in rituals by Siberian shamans, and in their out-of-body travels they frequently reach the moon.

The Moon and Death

Because of its monthly disappearance and return, the moon is often connected with the idea of mortal death and rebirth. In the Caroline Islands it is believed that in the beginning men rose from the dead, as did the moon. Every month they fell into a deep sleep when the moon became dark and awoke when the moon returned. An evil spirit disapproved of this and arranged for men to stay dead. In New Zealand, in a similar story, it is the culture hero Maui who wished men to live forever, but the moon said, "No, let them die and become like the soil."

In western Ceram, an island westward of New Guinea, a divine maiden was desired in marriage by the sun god. When her parents, disapproving, put a dead pig in her marriage bed as a substitute for her (perhaps a vestige of a changeover from human to animal sacrifice), the Sun caused her to sink into the ground. The girl called out to her parents, "Slaughter a pig and make a feast. In three days, look into the sky where I will be shining like a light." Thus the feast of the dead was instituted, and mortals for the first time saw the moon rising.

To the Siberian Inuit (Eskimo), death is conceived as loss of one's soul, which travels up to the moon and finally to the sun. This upward flight of the soul through the planets and stars is a widespread motif, found earliest among the Sumerians. It turns up again in Plato's Republic and in Cicero's Somnium scipionis, where the younger Scipio Africanus dreams he visits his grandfather in the heavens and looks down on all the celestial spheres. Below the moon, his grandfather tells him, all is chaos, but up here all is pure and serene.

The fullest account of the moon as the "abode of souls" is found in the essay De facie lunae by Plutarch (second century ce). Pythagorean philosophers had already taught that the Elysian Fields, the Greek isles of the dead, were situated on the sun and moon. In his essay Plutarch describes mortals as consisting of three parts: body, soul, and reason. In death the body is dissolved by Demeter, who stands for Mother Earth. The soul, together with reason, floats upward and, if pure, reaches the moon. If corrupt, it must wander between the earth and the moon until it is purified. The moon is ruled by Persephone, the Greek queen of the underworld, now transferred to the upper spheres. The souls who remain on the moon become beneficent spirits who return to earth to give oracles and help mortals in other ways. Gradually they are dissolved into pure reason and reach the sun.

In one of the earliest Indian Upanisads we are told that there are two roads open to souls after death: the road of flame and the road of smoke. The road of flame leads to the sun and the gods; the road of smoke to the moon, the ancestors, and reincarnation.

In the teaching of Mani, founder of the Manichaeans, the souls of those who have learned the truth during their lives are taken up to the wheel of the sun, where they are purified and passed on to the moon, here described as the superior station. Both of the luminaries are pictured as boats sailing to and fro in the upper atmosphere. When the moon becomes full of souls, it ferries them toward the East to the "aeons of light," who place them in the "pillar of glory," their final resting place. Then the moon, greatly reduced in size, returns for another load of souls.

The Moon and the Occult

Witches' meetings are held at the full moon, but the dark of the moon is the time for black sorcery. A practice known as "drawing down the moon" is pictured on Greek vases. In the Voyage of the Argo (Apollonius Rhodius, third century bce), Medea, the priestess of Hekate, is gathering herbs when the Moon addresses her, saying "How often have you disorbed me, making the nights moonless so you might practice your incantations." In this case the Moon would seem to be guiltless in the magic rites.

The lucky rabbit's foot must be taken in the dark of the moon, perhaps because the hare is one of the Moon's animals and she might protect it. According to Aelianos, a Greek writer of the third century ce, the moon causes epilepsy, which may be cured by a special kind of peony that, like the mandrake root, cannot be seen by day but must be gathered at night by tying to it a dog who pulls up the root and then dies (On Animals 24). This plant also cures afflictions of the eyes "in which moisture congeals and robs the eyes of their sight." Spells to reunite lovers are especially effective when cast by moonlight. In Theocritus (third century bce) a lovesick girl calls on the moon for help in her enchantment. The Roman poet Catullus (first century bce), in his hymn to Diana, calls her Trivia, Lady of the Crossroads (i.e., Hekate), and the "moon with counterfeit light." In the Middle Ages Diana was considered the ruler of witches, together with the "horned god." Pope John XII (tenth century) accused witches of "riding with Diana."

In dream divination, according to Artemidorus (Interpretation of Dreams, second century ce), "Intercourse with the Moon is entirely auspicious for shipmasters, pilots, merchants, astronomers, vagabonds and people fond of travelling. But for others it means dropsy. Selene the Moon represents both the wife and mother of the dreamer. She also represents prosperity, business ventures and navigation."

Thoth, the Egyptian god of measure and writing, was appointed by the sun god Re to take his place in the underworld as the moon. Thoth is also the god of magic and spells, like the Greek Hermes. In the Hellenistic period, the two were combined as authors of a series of magico-mystical writings under the name of Hermes Trismegistos.

In the astrology that took form in Alexandria around the second century bceas a combination of Near Eastern star lore and Greek mathematics, the moon, "when at its northern or southern limits helps in the direction of greater versatility, resourcefulness and capacity for change; in its rising, toward greater natural endowments, firmness and frankness; in its waning, towards dullness, less fixity of purpose and less renown" (Ptolemy, Tetrabiblos, second century ce).

In modern astrology, the moon "stands for the feminine, indrawn, receptive, and imaginative side. It tends toward carefulness, prudence, timidity, shyness, and the secluded life, though the lunar person is shrewd and practical in business" (Charles E. Carter, Principles of Astrology, London, 1969, p. 50).

The Moon in Folklore

Almost universal are cautions and devices to take advantage of the beneficent (and to avoid the unlucky) aspects of the moon, as well as theories to explain the moon spots. It has seemed an obvious ritual to farmers all over the world to plant during the waxing moon and reap during the waning moon, and this is still done in many parts of the United States. In pre-revolutionary France the law required trees to be felled during the waxing moon so that their wood would be drier. Hair, on the other hand, should be cut at the waning moon to make it thick. In England, shingles laid during the waning moon tend to swell. All over Europe, money, especially silver, the moon's metal, is exposed to the waxing moon or turned over in the pocket to make it grow. In Uganda, potters wait for the waxing moon before firing their pots. Warts are everywhere believed to grow as the moon waxes and to decrease at the wane.

Some Muslims in India practice a ritual called "drinking the moon." They fill a silver basin with water, let it reflect the light of the full moon, and drink it at a gulp as a remedy for palpitations and nervous disorders. Mothers in many places present their babies to the full moon so they will grow. In New Guinea, men on a hunting expedition leave their women at home to sing to the new moon for the success of the hunt. Natives of Greenland believe that women can become pregnant from sleeping in the light of the full moon. To prevent this, women wipe their abdomens with spittle. Weddings are variously believed to be lucky if held at the full moon or at the dark of the moon. The latter is explained by Plutarch (De facie lunae ), who claimed that the moon rushed to conjunction with the sun so that she might be refreshed by his light.

There are innumerable explanations for the spots that the West calls the "Man in the Moon." Some South American Indians believe they are ashes or menstrual blood smeared on the (male) Moon when he raped his sister the Sun. The Selk'nam of South America say they are the results of a beating the (female) Moon received when the Sun discovered that she had disclosed her initiation rites. The same spots are often described as a hare, a frog, a snail, or some other animal or as some mortal lured up to the moon. In Scandinavian mythology they are a boy and girl carrying water, supposed to be the prototypes of Jack and Jill. The Shawnee Indians see in the spots their creator goddess bending over a cooking pot. Among the Malay, they are an old man making a fishing line under a banyan tree. At the other end of the line is a rat, who is eating the line as fast as the man can make it. When the old man is finished, he will use the line to catch everything on the earth and reel it up to the moon.

There is widespread belief that the light of the full moon turns humans who are so disposed into werewolves and causes lunacy if one sleeps in its beams. Very common in Europe and America is the idea that, during the night of the full moon, more crimes are committed, more children are born, and more patients committed to mental hospitals than at other times.

See Also

Feminine Sacrality.

Bibliography

Since there are few books devoted to the religious and mythological aspects of the moon, most information on the subject must be extracted from religious writings and from histories of the religions of different areas. The most important source for ancient Mesopotamia and Egypt is volume 1 of The Ancient Near East, edited by James B. Pritchard (Princeton, 1973). For the origin of the calendar, an excellent account is Elias J. Bickerman's Chronology in the Ancient World (Ithaca, N.Y., 1968). By far the most complete book on the development of astrology is still Auguste Bouché-Leclerq's L'astrologie grecque (Paris, 1899). Franz Cumont's Recherche sur le symbolisme funeraire des Romains contains an unusual amount of data on alien sects of the Hellenistic and Roman periods. An essay by Mircea Eliade entitled "The Moon and Its Mystique," in Patterns in Comparative Religion (New York, 1958), provides many insights into the symbolism and iconography of the moon. The same author's Shamanism: Archaic Techniques of Ecstasy, rev. & enl. ed. (New York, 1964), gives a background for the religions of Siberia and the American Indians. For folklore on the moon a good source is the Funk and Wagnall's Dictionary of Folklore, Mythology and Legend (New York, 1950). Åke Hultkrantz, in Religions of the American Indians (Los Angeles, 1979), gives a concise but thorough summary of the beliefs of the Indians of North and South America. The most recent and fullest account of the religions of the Near East is found in Thorkild Jacobsen's The Treasures of Darkness: A History of Mesopotamian Religion (New Haven, 1976). The best, most complete book on the subject of the moon is La lune: Mythes et rites, edited by Denise Berndt (Paris, 1962), with essays by separate authors on various areas of the world. Some new insights and original research appear in Julius Lewy's "The Late Assyro-Babylonian Cult of the Moon and Its Culmination at the Time of Nabonidus," Hebrew Union College Annual (19451946): 405489. An extremely useful collection of material from all over the world is The Mythology of All Races, 13 vols., edited by Louis Herbert Gray and George Foot Moore (Boston, 19161932), under the auspices of the Archaeological Institute of America. Martin P. Nilsson brings to his Geschichte der griechischen Religion (Munich, 1955) a wealth of information on archaeology and comparative religion. Still the most complete collection of mythological material is Ausführliches Lexikon der griechischen und römischen Mythologie, 7 vols. in 10, edited by W. H. Roscher (18661893; Hildesheim, 1965). The series "Sacred Books of the East" (18791910), containing the sacred writings of India and Persia collected by F. Max Müller, was reissued at Delhi in 1965.

New Sources

Beaulieu, Paul-Alain. "The Babylonian Man in the Moon." Journal of Cuneiform Studies 51 (1999): 9199.

Keel, Othmar. Goddesses and Trees, New Moon and Yahweh: Ancient Near Eastern Art and the Hebrew Bible. Sheffield, U.K., 1998.

Komaroff, Katherine. Sky Gods: The Sun and Moon in Art and Myth. New York, 1974.

López Austin, Alfredo. Rabbit on the Face of the Moon: Mythology in the Mesoamerican Tradition. Salt Lake City, 1996.

Neyrolles, Olivier. Lune (Moon). Paris, 1999.

Ornan, Tallay. "The Bull and Its Two Masters: Moon and Storm Dieties in Relation to the Bull in Ancient Near Eastern Art." Israel Exploration Journal 51/1 (2001): 126.

Sermonetti, Giuseppe. Fiabe di luna: simboli lunari nella favola, nel mito, nella scienza (Moon stories: moon symbols in fable, myth and science). Milan, 1986.

Theuer, Gabriele. Der Mondgott in den Religionen Syrien-Palästinas. Freiburg, Switzerland, 2000.

Jean Rhys Bram (1987)

Revised Bibliography

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moon

moon The moon is the most ‘human’ of the heavenly bodies, since its phases and the shadows on its surface give it a face, encouraging the popular lore about the ‘Man in the Moon’. Belief that the moon has a special influence on human affairs has been universal. Because of its phases, it has been linked to the rhythms of life and to nature's cycles: water, rain, and fertility. ‘The moon has great influence in vulgar philosophy’, observed Samuel Johnson, touring the Scottish Highlands, ‘In my memory it was a precept annually given in one of the English Almanacks, to kill hogs when the moon was increasing, and the bacon would prove the better in boiling.’

Many religious beliefs have been woven around the moon, which has commonly been personified as a goddess. She is Ishtar to the Babylonians, Asthoreth to the Phoenicians, and, to the Greeks, Artemis (Roman Diana), the chaste huntress who cruelly punished those who failed to worship her.

Three main connotations have been ascribed to the moon. It has stood for the feminine principle. Being smaller than the sun and reflecting its light, the moon has been taken to represent female dependence and passivity. In Taoist terms, the moon is thus yin, being receptive, relative to the sun's yang. Amongst the Inca, the moon was the sun's wife, and hence the goddess of women. Its waxing and waning has also served as an analogue for supposed female fickleness.

The moon has also been regarded as controlling menstruation. According to the eighteenth-century physician, Richard Mead, ‘everyone knows how great a share the Moon has in forwarding those evacuations of the weaker sex.’ The very word menstruation means ‘moon change’, while in France it is called ‘le moment de la lune’. In Saibai and Yam, two islands off Australia, it was believed that menstruation was caused by the moon, who came as a man to seduce the pubescent girl.

Menstrual seclusion rituals are thus commonly governed by the lunar phases. The Juluo of East Africa believe that menstruation comes with the new moon and that only then can women become pregnant. There have been evolutionary speculations that since the lunar and the menstrual cycles each are of approximately 28 days' duration, menstruation is causally related to the action of the moon on the tides, somehow dating back to the time when we were all sea creatures.

Finally, the moon has been judged to be the cause of madness, the term ‘lunacy’ deriving from the Latin luna, meaning moon. Hippocrates, Pliny the Elder, Plutarch, and the Bible all affirmed its harmful influence. Aretaeus of Cappadocia and Rhazes held that epileptic seizures were governed by the moon, while Hildegard of Bingen deemed that ‘a male born on the seventeenth day of the Moon will be an idiot.’ Shakespeare affords many references to the Moon as the ‘sovereign mistress of true melancholy’:It is the very error of the moon,
She comes more near the earth than she was wont
And makes men mad. (Othello)


As late as 1791, the French psychiatrist Joseph Daquin wrote in his Philosophie de la Folie that ‘it is a well established fact that insanity is a disease of the mind upon which the moon exercises an unquestionable influence.’ His younger contemporary, Jean Esquirol, concluded that the moon affected the insane through its light, which excited some and terrified others. Although such beliefs have waned, many modern studies have investigated the significance of the phases of the moon in relation to suicide, murder, mental hospital admissions, violence, migraine, anxiety, childbirth, and marital breakdown.

Roy Porter

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moon

moon the constantly recurring changes and phases of the moon have caused it to be taken as a type of changeableness and inconstancy; they were also traditionally supposed to influence the health of body and mind, and to cause insanity.

The moon may also be personified as a goddess (for example, Diana or Cynthia), and as such symbolizes virginity.

Recorded from Old English (in form mōna) and of Germanic origin, related to month, the word comes from an Indo-European root shared by Latin mensis and Greek mēn ‘month’, and also Latin metiri ‘measure’ (the moon being used to measure time).
believe that the moon is made of green cheese believe an absurdity, an expression recorded from the 16th century. The origin is not clear, but may refer to the mottled appearance of a cheese like sage Derby being held to resemble the variegated surface of the moon.
Moon Festival a Chinese festival held in the middle of the autumn, originally a family gathering after the completion of the harvest.
Moon Hoax a series of articles printed in the New York Sun of August 1835, purporting to reveal the discovery by the astronomer John Herschel of life on the moon, including mountains, forests, winged inhabitants, and beavers walking on two legs. The story, which excited great public interest and substantially increased the circulation of the paper, was revealed the following month as a hoax; the author was the British journalist Richard Adams Locke (1800–71).
over the moon extremely happy; delighted. The expression comes from The Cow jumped over the Moon, a line from a nursery rhyme.

See also blue moon, cry for the moon, glimpses of the moon, man in the moon, no moon, no man.

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Moon

Moon (emblem of Islam): see CRESCENT MOON.

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Moon

Moon

The moon, the largest and brightest object in the night sky, has long inspired curiosity and wonder. It appears at night, the time of sleep and dreaming that sometimes seems to approach the borders of death and the afterlife. Radiating an air of mystery and magic, the moon is also associated with love and often serves as a symbol of unattainable beauty.

Unlike the sun, the moon does not present the same face every day. It waxes, or grows larger, until it becomes a glowing silver-white disk. Then night by night it wanes, or shrinks, to a curved sliver until it vanishes altogether. A few days later a slender new moon appears and begins to grow again in an endless cycle that


* See Names and Places at the end of this volume for further information.

repeats each month. In ancient times, people used these phases of the moon to measure time.


Themes and Beliefs. The moon's waxing and waning have made it a symbol of time, change, and repetitive cycles around the world. One such cycle is the constant alternation of birth and death, creation and destruction. People have linked the moon with both birth and death.

The Polynesian islanders of the Pacific Ocean said that the moon was a creator goddess named Hina and that women called wahines were her representatives on earth. In ancient Persia*, the moon was Metra, the world mother.

For some people the moon had a destructive aspect. The Aztecs of Mexico called it Mictecacuiatl and believed that it traveled through the night skies hunting out victims to consume. The Maori people of New Zealand referred to the moon as "man eater." Africans and Semitic* peoples of the ancient Near East also feared this terrifying aspect of the moon.

In certain cultures, the moon had a gentler association with death. Some ancient Greek sects thought that the moon was the home of the dead, and early Hindus believed that the souls of the dead returned to the moon to await rebirth. The moon could even symbolize birth and death at the same time. The Tartars of Central Asia called it the Queen of Life and Death.

In mythology the moon is often female, a goddess who may be paired with a sun god. The Incas of South America told of a brother and sister, the moon maiden and the sun man, who were the ancestors of the royal Incas. In the Mayan writing system, a symbol showing the moon goddess seated inside the moon was used before the names of noble women. The Greeks associated the moon with the goddess Artemis*, sister of Apollo. They also called it Hecate, Cynthia, and Selene. The Roman name for the moon was Luna. Native American names for the moon include the Old Woman Who Never Dies and the Eternal One.

Sometimes, however, the moon is male. The Inuit of Greenland picture the moon as a hunter sitting in front of his igloo. Norse* mythology speaks of a moon son and a sun daughter, and Mrs. Sun and Mr. Moon are part of German folklore.

sect religious group

Other legends explain the appearance of the moon, whose mottled surface has suggested various shapes and identities. The "man in the moon" is one common interpretation thought to have originated from the biblical book of Numbers, which describes a man carrying a load of sticks. People have also interpreted the shapes as frogs and toads, and rabbits in the moon occur in many mythologies. In China and Japan the lunar rabbit is said to mix a potion that gives immortality.


The Moon in Myths. A Native American myth says that the sun and moon are a chieftain and his wife and that the stars are their children. The sun loves to catch and eat his children, so they flee from the sky whenever he appears. The moon plays happily with the stars while the sun is sleeping. But each month, she turns her face to one side and darkens it (as the moon wanes) to mourn the children that the sun succeeded in catching.

The Efik Ibibio people of Nigeria in West Africa also say that the sun and the moon are husband and wife. Long ago they lived on the earth. One day their best friend, flood, came to visit them, bringing fish, reptiles, and other relatives. Flood rose so high in their house that they had to perch on the roof. Finally he covered the house entirely, so the sun and moon had to leap into the sky.

According to the Greek myth of Endymion and Selene, the moon (Selene) fell in love with a handsome young king named Endymion and bore him 50 daughters. One version of the story says that Selene placed Endymion in eternal sleep to prevent him from dying and to keep him forever beautiful.

In a myth of the Luyia people of Kenya in East Africa, the sun and moon were brothers. The moon was older, bigger, and brighter, and the jealous sun picked a fight with him. The two wrestled and the moon fell into mud, which dimmed his brightness. God finally made them stop fighting and kept them apart by ordering the sun to shine by day and the mud-spattered moon to shine by night to illuminate the world of witches and thieves.

Going Moon-Mad

People once believed that moonlight had a powerful effect on human behavior. Those who acted strangely were said to be "moonstruck," and lunacy, a term for madness, comes from Luna, the Latin name for the moon goddess. The Japanese believed that the moon was a god with powers to foretell the future. Priests would study the moon's reflection in a mirror, believing that if they gazed directly at the moon, it might drive them mad. Superstitions about the moon's evil influence made some people refuse to sleep in a place where moonbeams could touch them. In the 1200s, the English philosopher Roger Bacon wrote, "Many have died from not protecting themselves from the rays of the moon."

lunar relating to the moon

immortality ability to live forever

A myth from the Indonesian island of Java tells how Nawang Wulan, the moon goddess, came to earth to bathe in a lake. A man stole her cloak of swan's feathers so she could no longer fly back up into the sky, and she stayed on earth and married him. Nawang Wulan used her magic powers to feed the household every day with just a single grain of rice. When her husband discovered her secret, she lost her magic power and had to gather and pound rice every day like all other wives. However, she did find her swan-feather cloak and used it to return to the sky. She stayed there at night but spent the daylight hours on earth with her husband and daughter.

See also Hecate; Sun.

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moon

moonafternoon, attune, autoimmune, baboon, balloon, bassoon, bestrewn, boon, Boone, bridoon, buffoon, Cameroon, Cancún, cardoon, cartoon, Changchun, cocoon, commune, croon, doubloon, dragoon, dune, festoon, galloon, goon, harpoon, hoon, immune, importune, impugn, Irgun, jejune, June, Kowloon, lagoon, lampoon, loon, macaroon, maroon, monsoon, moon, Muldoon, noon, oppugn, picayune, platoon, poltroon, pontoon, poon, prune, puccoon, raccoon, Rangoon, ratoon, rigadoon, rune, saloon, Saskatoon, Sassoon, Scone, soon, spittoon, spoon, swoon, Troon, tune, tycoon, typhoon, Walloon •fortune, misfortune •vodun • veldskoen • honeymoon •forenoon • tablespoon • teaspoon •soupspoon • dessertspoon • Neptune •tribune • triune • opportune

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moon

moon the satellite of the earth OE.; (lunar) month XIV. OE. mōna = OS. māno (Du. maan fem.), OHG. māno (G. mond), ON. māni, Goth. mēna :- Gmc. *mænan-, prob. rel. to *mænōþ- MONTH: cogn. words for ‘moon’ and ‘month’ based on *mēn(e)s- are L. mēnsis month, Gr. meís, mḗn month. mḗnē moon. Skr. mā́s- moon, month, Ir. mi month, OSl. mēsęcl̂ moon, month; referred ult. to the IE. base *mē-, as in L. mētīrī MEASURE, the moon being the star by which time is measured.

The foll. comps. are of special interest: mooncalf † false conception XVI; born fool XVII; perh. after G. mondkalb; cf. G. mondkind, MLG. maanenkind ‘moon-child’. moonlight XIV; hence moonlighting operation (esp. illicit) by night. XIX. moonlit XIX. moonshine moonlight; appearance without substance, empty talk, etc. XV. moonstone XVII; after L. selēnitēs SELENITE. moonstruck deranged, as if by the influence of the moon (cf. lunatic). XVII.

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Moon

454. Moon

  1. Artemis (Rom. Diana ) goddess of the moon. [Gk. Myth.: Kravitz, 36; Brewer Dictionary, 727]
  2. Astarte (Ashtoreth ) personification of moon in crescent stage. [Phoenician Myth.: Brewer Dictionary, 726727]
  3. Bast cat-headed goddess representing sun and moon. [Ancient Egyptian Rel.: Parrinder, 42]
  4. Cynthia goddess of the moon. [Gk. Myth.: Kravitz, 72]
  5. Endymion name of man in the moon. [Gk. Myth.: Brewer Dictionary, 376377]
  6. Hecate personification of the moon before rising and after setting. [Gk. Myth.: Brewer Dictionary, 726727]
  7. Luna ancient Roman goddess personifying the moon. [Rom. Myth.: Zimmerman, 153]
  8. Nokomis daughter of the Moon and grandmother of Hiawatha. [Am. Lit.: Longfellow The Song of Hiawatha in Magill I, 905]
  9. Petrus caretaker of Heaven; makes sure moon shines on whole earth. [Ger. Opera: Orff, The Moon, Westerman, 115116]
  10. Phoebe moon as sister of sun (Phoebus). [Gk. Myth.: Brewer Dictionary, 726727]
  11. Selene the moon as lover of sleeping shepherd Endymion. [Gk. Myth.: Brewer Dictionary, 726727]

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Moon

MOON

MOON (Heb. usually יָרֵחַ, yare'aḥ; poetical form לְבָנָה, levanah; Isa. 24:23, 30:26; Song 6:10). A deity for ancient Israel's neighbors, the moon is for Israel "the lesser light" created on the fourth day of creation "to rule the night" (Gen. 1:16). The calendar used in ancient Israel was probably lunisolar. At any rate, the month was based on the periodical recurrence of the moon's phases. (For full details, see *Calendar.) The New Moon, Rosh Ḥodesh, the beginning of a new period, was proclaimed by the Sanhedrin and marked by the blowing of trumpets and special offerings (Num. 10:10, et al.), and was a minor holiday of which liturgical traces have remained (see *New Moon). Two main festivals, Passover and Sukkot, begin at the full moon.

Cult

As a male deity, the moon (Nanna) was worshiped by the Sumerians and by the Semites in general. Known as Sin among the eastern Semites, the moon god was called Eraḥ in the "west." Sin was the patron god of Ur and Haran, which were connected with the origins of the Patriarchs. The popularity of the moon cult is attested by the frequency of theophoric names with the divine element Sin or Eraḥ. The Israelites were warned against worshiping the moon, and convicted transgressors were punished by stoning (Deut. 4:19, 17:3–5). The moon cult was, nevertheless, introduced into Judah by King Manasseh (ii Kings 21:3) but was subsequently abolished by King Josiah (ii Kings 23:5).

For fuller details see *Host of Heaven.

In the Aggadah

Rabbinic literature uses levanah, and not yare'ah for the moon. The moon and the sun were created on the 28th of Elul (pdre 8), and were originally equal in size (both being referred to as "the two great lights" – Gen. 1:16), but jealousy between them caused dissensions, so that God decided to make one of them smaller. The moon was chosen to be degraded because it had unlawfully intruded into the sphere of the sun, and hence the difference between the sun, "the greater light." and the moon, "the lesser light," (ibid.). The unlawful intrusion is based on the phenomenon that the moon is sometimes visible during the day (pdre 6; Gen. R. 6:3). The remarkable statement is made that the he-goat offered on the New Moon is a sin-offering brought by God; according to the Midrash this was for having permitted the moon to encroach upon the domain of the sun (Gen. R. 6:3), but the Talmud says it was for diminishing its size (Ḥul. 60b). God also appeased the moon by surrounding it with stars like a viceroy encircled by his assistants (Gen. R. 6:4). God's original intention was that the sun alone should furnish light to the earth, but foreseeing the future idolatrous worship of the heavenly objects, He decided that it would be better to have two large celestial bodies, thus minimizing the danger of one becoming a central deity (Gen. R. 6:l). For this reason the sun and moon stand in judgment daily before the Almighty, ashamed to go forth, and pleading, "People worship us and anger the Holy One, blessed be He!" (Mid. Ps. 19:11).

The moon was designated as Jacob's luminary, while the sun symbolized Esau. The Jewish nation bases its calendar on the lunar year, since they have a portion in this world and the world to come, like the moon which can be seen both by day and by night (Gen. R. 6:3). An eclipse of the moon is therefore considered an evil omen for Israel, and is attributed to four different sins: forgery, false testimony breeding small cattle in Ereẓ Israel (since they damage the crops of the field), and cutting down fruit trees (Suk. 29a). The rabbis declared that the countenance of Moses was like that of the sun, while that of Joshua was like that of the moon (bb 75a). Esther, who brought light to Israel after the evil decree of Ahasuerus, is likewise compared to the moon, which enables people to rejoice and walk about when it illuminates the darkness of the night (Ex. R. 15:6). In the future, seven companies of righteous men whose faces will shine like the sun and the moon will welcome the presence of God (Lev. R. 30:2). Moses did not comprehend exactly when the New Moon was to be sanctified until God showed him the form of the moon when it was beginning its monthly cycle and said to him. "When you see it like this, sanctify it" (Mekh. Pisḥa 1).

bibliography:

Ginzberg, Legends, index s.v.Moon.

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Moon

Moon

Phases and eclipses

The lunar surface

Moon rocks

Lunar ice

Lunar origin

Dynamic moon

Recent and future missions to the moon

Resources

The moon (sometimes referred to as Luna), Earths only natural satellite, is a roughly spherical, rocky body that orbits the Earth at an average distance of 238,000 mi (382,942 km). Its diameter is about one-fourth Earths diameter. Compared to moons of other planets, this is a large relative size. The diameters of other moons within the solar system are a much smaller fraction of their planets diameter.

The mass of the moon is only about one-eightieth (1/80th) the mass of Earth, so the force of gravity is smaller. On the moon, the acceleration due to gravity is only one-sixth that of Earths gravity. Accordingly, masses weigh one-sixth as much on the moon when compared to weights on Earth. For example, an

astronaut that weighs 180 lbs (81.6 kg) on Earth, would weigh 30 lbs (27.2 kg) on the moon. The astronauts who landed there could leap high and long with very little effort because of the reduced gravitational force. This is, also, why the moon has no atmosphere. The escape velocity of the moon, which is related to the mass of the planet, is very lowabout the same as the velocity due to collisional motion in an atmospheric gas mixtureso any atmosphere that might have once formed would have easily escaped the pull of the moons gravity.

The view of the moon from Earth remains the same (viewing the same face all of the time) because it rotates on its axis at the same rate that it travels around Earthonce every 29.5 days. This is no mere coincidence. The side of the moon facing the Earth is attracted more strongly by Earths gravitational force than the opposite side. The force of gravity depends on the mass of the two interacting objects (here the Earth and the moon), and the moon has a mass asymmetry. That is, there is more mass concentrated in the half of the moon seen from Earth than in the other half. The effect is called gravitational locking and is a common occurrence in the solar system.

Phases and eclipses

Observations of the moon from Earth reveal different phases of the moon with respect to the percentage of lunar surface reflecting sunlight back to Earth. As the moon orbits Earth, it comes between Earth and the sun once a month at the time of a new moon, and orbits Earth in very nearly the same plane that Earth orbits the sun. If the moons orbital plane had zero tilt off Earths orbital plane, a total lunar eclipse would be visible every month.

There is actually about a 20° tilt, so total eclipses over selected area occur only about seven times a year, when Earth is directly between the sun and the moon. Earths shadow falls on the full moon, and it slowly becomes dark and then bright again as it moves out of Earths shadow.

The lunar surface

Although surface features were observed as early as 1600 by Italian astronomer and physicist Galileo Galilei (15641642), most information regarding the surface is from spacecraft exploration.

In 1959, the Soviet Union (now, Russia) sent the first spacecraft to orbit the moon, sending back tantalizing photographs. American astronauts orbited the moon in 1968 and landed manned expeditions from 1969 to 1972. American astronaut Neil Armstrong (1930) was the first human to walk on the moon, which he did in July 1969. Six missions landed during those years, providing copious data from the lunar surface. Apollo experimentation included soil-testing devices, cameras, seismometers, solar wind collectors, and rock collection. The Soviet Union also landed an unmanned craft during this time (1970), collecting additional data for analysis.

Moon rocks

Spacecraft experimentation found mostly igneous rock on the moon (rock formed by cooling lava) but some sedimentary. The sedimentary rock was probably formed by falling debris after meteoritic impacts. The igneous rock in the marina is mostly basalt, but the highlands are mostly anorthosites. Both types form from cooling lava but under different conditions and at different cooling rates.

Radioactive dating of rocks brought back by the Apollo astronauts yields an absolute age (the time since the rocks solidified) of the highlands as 3.9 to 3.8 billion years, with the final lava flow around 3 billion years ago.

The moon has no overall magnetic field. According to the currently favored model of planetary magnetic fields (the dynamo model), this means either that the moon probably has no molten core or that only a very small part of the core is molten. There is a weak magnetic field frozen into the rocks, however, or the rocks have a north pole and a south pole, so it is

possible that the moon once had a magnetic field surrounding it.

Lunar ice

In 1998, ice was found in the moons craters by the orbiting American spacecraft Lunar Prospector. The frozen water is in the form of ice crystals mixed with dirt, and was found covering each of the moons poles in relatively large amounts. It is possible that such water could someday be retrieved out of the moons dirt and used by human colonies living permanently on the moons harsh surface.

Lunar origin

The fact that the oldest rocks on the moon are about the same age as the oldest rocks found on Earth indicates that the two were formed around the same time. Rather than forming by gravitational clumping of matter in orbit around Earth, however, the moon is probably a captured asteroid. Studies of the differences in the compositions of Earth and the moon indicate that, during the early stages of Earths formation, a large asteroid struck Earth a glancing blow, and pieces of it, as well as pieces of Earth, flew back up to orbit Earth in a ring like system around the planet. Eventually, the force of gravity caused the fragments to coalesce and form the moon. This is called the ring ejection theory of lunar origin.

Dynamic moon

In 2003, astronomers announced that data and observations indicated one particular crater might well be classified as the youngest crater thus far discovered. The crater, formed in 1953 by an asteroid impact, is the only known lunar crater to have been formed during recorded human history. New and more powerful telescopes, along with orbiting satellite photographs now allow examination of the impact site. Astronomers have observed indications of a fresh crater in the impact zone (i.e., the area corresponding to the impact flash observed in 1953).

Although impacts continue, and thus new crater formation is a continuous event, the crater at the 1953 impact site is the first new crater to be observed.

The object that struck the moon is estimated to have been about 328 yd (300 m) across. The estimated energy released from impact would have been the equivalent of approximately that observed from the detonation of one-half megaton of TNT (more than 30 times more energetically destructive than the atomic bomb dropped on Hiroshima, Japan, during World War II).

Recent and future missions to the moon

SMART-1 (Small Missions for Advanced Research in Technology), a Swedish-designed spacecraft used by the European Space Agency, was launched from the French Guiana on September 27, 2003. The mission of SMART-1 consisted of mapping the lunar surface with x-ray and infrared imaging, determining its chemical composition using x-ray spectroscopy, searching for frozen water at the south pole with infrared light, and mapping several mountaintops of the moon. After completing is mission to the moon, it was intentionally directed to crash into the surface of the moon on September 3, 2006, so that scientists on Earth could study a simulated meteor impact.

Japan is developing a mission to the moon around 2007 called Lunar-A (JAXA Lunar Orbiter and Penetrator Mission). Around the same time, India is working on a mission it calls Chandrayaan-1 (ISRO Lunar Orbiter Mission). Russia and China are considering joint missions to the moon, and the United States is expected to return to the moon sometime after 2015 with its new Orion spacecraft, which is the replacement for the space shuttle fleet (scheduled for retirement in 2010).

See also Planetary geology; Spacecraft, manned.

Resources

BOOKS

Bakich, Michael A. The Cambridge Planetary Handbook New York: Cambridge University Press, 2000.

Light, Michael, and Andrew Chaikin. Full Moon. New York: Knopf, 2002.

Moore, Patrick. On the Moon. London, UK: Cassell, 2001.

Schmitt, Harrison H. Return to the Moon: Exploration, Enterprise, and Energy in the Human Settlement of Space. New York: Copernicus Books, 2006.

Wlasuk, Peter. Observing the Moon (Practical Astronomy). New York: Springer Verlag, 2002.

OTHER

Williams, David R., NASA, National Space Science Data Center. The Moon <http://nssdc.gsfc.nasa.gov/planetary/planets/Moonpage.html> (accessed October 18, 2006).

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Moon

Moon

The Moon was the subject of widespread folklore in ancient times. While the brightest object in the night sky, it is not so bright that its surface texture is obscured. The patterns on the lunar surface have, like clouds, taken on anthropomorphic characteristics. Some saw the face of a man; others, various animals. The changing phases of the Moon and its seeming disappearance for a day or two each month also led to additional speculations. Modern werewolf lore has the wolf-like side of the person showing itself only during the evenings of the full Moon.

The Moon was associated with various gods and goddesses, though primarily the latter. In Hindu astrology, the Moon was associated with the god Nanna, though the more common associations are with the Greek Artemis, the Roman Luna, or the Moonlight-Giving Mother of the Zuni. It was especially associated with females as they identified the lunar cycle with the menstrual cycle. In the contemporary world, the Moon has assumed a central role in the mythology developed by Neo-Paganism, especially its feminist element.

The most comprehensive system for gathering the many observations about the Moon, attempting to understand its significance and drawing implications for behavior from it, was astrology. The 28-day cycle of the Moon became a convenient way of dividing the solar year into more manageable units we have come to know as months. (Actually the Moon takes only 27.32 days to orbit the earth, but because of the movement around the Sun it takes 29.53 days for it to complete a cycle from full Moon to full Moon.

In astrology the Moon represents the inner emotional side of the self, the subconscious mind and psyche. The Moon's placement in the chart reveals the creative side of the person, where he/she might give birth to new ideas, how his/her nurturing side is expressed, or where great passion is resting. The Moon is paired off with the Sun, related to the overall aspects of one's outer visible life.

Over the years, from folklore and astrology, the Moon was identified with a variety of behavior patterns, most notably mental disorders, or lunacy. The moon has been seen as effecting crime, suicides, accidents, and births, their occurrences believed to rise and fall with the phases of the Moon. It is believed by many still that, for example, the Moon will stimulate pregnant women to give birth, an observation bolstered by the alternating full and empty birth wards nurses have reported at hospitals. These observations have become the subject of research through the twentieth century, though many of these studies have been somewhat buried in various psychological journals.

In the 1980s and 1990s psychologists I. W. Kelly and R. Martens were the focus of several studies testing lunar assumptions beginning with a sweep of the literature in 1986 attempting to discover any evidence for a correlation between lunar phases and birthrates. They discovered that studies had been done in various settings in different countries with large samples, but that no data tied a higher rate of spontaneous births to a particular phase of the Moon. A similar negative correlation has been found between the Moon and an upsurge of behavior associated with mental illness or suicide (including number of suicides, attempts at suicides, or threats of suicide).

Early in 2000, news reports appeared of a German study that showed a statistical correlation between the Moon phases and alcohol consumption. However, on checking, the report appeared to have garbled the original report written by Hans-Joachim Mittmeyer of the University of Türbingen and Norbert Filipp of the Health Institute in Reutlingen. The pair of researchers had done a study of arrests for alcohol in Germany over a lunar cycle without finding any statistically significant variations from day to day.

While much interesting and suggestive data on astrological relationships have been produced over the twentieth century, especially that associated with Michel Gauquelin, the data on the immediate effects of the Moon on behavior as expressed in popular folklore appears to be negative. While there remain areas that have gone unresearched, enough has been done so that the burden of proof has shifted onto the shoulders of those who now make such claims.

Sources:

Carrol, Robert Todd. "Full Moon and Lunar Effects." Skeptic's Dictionary. http://www.skepdic.com/fullmoon.html. June 11, 2000.

Chudler, Eric. "Moonstruck! Does the Full Moon Influence Behavior." http://faculty.washington.edu/chudler/moon.html. June 11, 2000.

Kelly, I. W., and R. Martens. "Lunar Phases and Birthrate: An Update." Psychological Reports 75 (1996): 507-11.

, James Rotton, and Roger Culver. "The Moon Was Full and Nothing Happened: A Review of Studies on the Moon and Human Behavior and Human Belief." In J. Nickell, B. Karr, and T. Genoni, eds. The Outer Edge. Amherst, N.Y.: CSICOP, 1996.

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Moon

Moon

Earth's moon is a roughly spherical, rocky body orbiting Earth at an average distance of 238,000 mi (382,942 km). Its diameter is about one-fourth Earth's diameter. Compared to moons of other planets, this is a large relative size. The diameters of other moons are a much smaller fraction of their planets' diameter.

The mass of the Moon is only about 1/80 the mass of the Earth, so the force of gravity is smaller. On the Moon the acceleration due to gravity is only one-sixth Earth's. Accordingly, masses "weigh" one-sixth as much on the Moon. The astronauts who landed there could leap high and long with very little effort because of the reduced gravitational force. This is also why the Moon has no atmosphere. The escape velocity of the Moon, which is related to the mass of the planet , is very low—about the same as the velocity due to collisional motion in an atmospheric gas mixture—so any atmosphere that might have once formed would have easily escaped the pull of the Moon's gravity.

The view of the Moon remains the same (viewing the same face) because it rotates on its axis at the same rate that it travels around the Earth—once every 29.5 days. This is no mere coincidence. The side of the Moon facing us is attracted more strongly by Earth's gravitational force than the opposite side. The force of gravity depends on the mass of the two interacting objects (here the Earth and the Moon) and the Moon has a mass asymmetry. There is more mass concentrated in the half of the Moon we see than in the other half. The effect is called "gravitational locking" and is a common occurrence in our solar system .

Phases and eclipses

Observations of the Moon from Earth, reveal different phases of the Moon with respect to the percentage of lunar surface reflecting sunlight back to Earth. As the Moon orbits Earth, it comes between Earth and the Sun once a month at the time of a new Moon, and orbits Earth in very nearly the same plane that the Earth orbits the Sun. If the Moon's orbital plane had zero tilt off the Earth's orbital plane, a total lunar eclipse would be visible every month.

There is actually about a 20° tilt, so total eclipses over selected area occur only about seven times a year, when the Earth is directly between the Sun and the Moon. The Earth's shadow falls on the full Moon, and it slowly becomes dark and then bright again as it moves out of the Earth's shadow.

The lunar surface

Although surface features were observed as early as 1600 by Galileo, most information regarding the surface is from spacecraft exploration.

In 1959 the Soviet Union sent the first spacecraft to orbit the Moon, sending back tantalizing photographs. American astronauts orbited the Moon in 1968 and landed manned expeditions from 1969 to 1972. Six landed during those years, providing copious data from the lunar surface. Apollo experimentation included soil-testing devices, cameras, seismometers, solar wind collectors, and rock collection. The Soviet Union also landed an unmanned craft during this time (1970), collecting additional data for analysis.


Moon rocks

Spacecraft experimentation found mostly igneous rock on the Moon (rock formed by cooling lava) but some sedimentary. The sedimentary rock was probably formed by falling debris after meteoritic impacts. The igneous rock in the marina is mostly basalt, but the highlands are mostly anorthosites. Both types form from cooling lava but under different conditions and at different cooling rates.

Radioactive dating of rocks brought back by the Apollo astronauts yields an absolute age (the time since the rocks solidified) of the highlands as 3.9 to 3.8 billion years, with the final lava flow around 3 billion years ago.

The Moon has no overall magnetic field. According to the currently favored model of planetary magnetic fields (the dynamo model), this means either that the Moon probably has no molten core or that only a very small part of the core is molten. There is a weak magnetic field frozen into the rocks, however, or the rocks have a north pole and a south pole, so it's possible that the Moon once had a magnetic field surrounding it.


Lunar ice

In 1998 ice was found in the Moon's craters by the orbiting American spacecraft Lunar Prospector. The frozen water is in the form of ice crystals mixed with dirt, and was found covering each of the Moon's poles in relatively large amounts. It is possible that such water could someday be retrieved out of the Moon's dirt and used by human colonies living permanently on the Moon's harsh surface.


Lunar origin

The fact that the oldest rocks on the Moon are about the same age as the oldest rocks found on Earth tells indicates that the two were formed around the same time. Rather than forming by gravitational clumping of matter in orbit around the Earth, however, the Moon is probably a captured asteroid. Studies of the differences in the compositions of the Earth and Moon indicate that, during the early stages of the Earth's formation, a large asteroid struck the Earth a glancing blow, and pieces of it, as well as pieces of Earth, flew back up to orbit the Earth in a ring-like system around the planet. Eventually, the force of gravity caused the fragments to coalesce and form our Moon. This is called the "ring ejection theory" of lunar origin.


Dynamic Moon

In 2003, astronomers announced that data and observations indicated one particular crater might well be classified as the youngest crater thus far discovered. The crater, formed in 1953 by an asteroid impact, is the only known lunar crater to have been formed during recorded human history. New and more powerful telescopes, along with orbiting satellite photos now allow examination of the impact site and astronomers observed indications of a fresh crater in the impact zone (i.e., the area corresponding to the impact flash observed in 1953).

Although impacts continue, and thus new crater formation is a continuous event, the crater at the 1953 impact site is the first new crater to be observed.

The object that struck the Moon is estimated to have been about 328 yd (300 m) across and the estimated energy released from impact would have been the equivalent of approximately that observed from the detonation of one-half megaton of TNT (more than 30 times more energetically destructive than the atomic bomb dropped on Hiroshima).

See also Planetary geology; Spacecraft, manned.

Resources

books

Bakich, Michael A. The Cambridge Planetary Handbook. New York: Cambridge University Press, 2000.

Light, Michael, and Andrew Chaikin. Full Moon. New York: Knopf, 2000.

Wlasuk, Peter. Observing the Moon (Practical Astronomy). New York: Springer Verlag, 2002.

other

Williams, David R., NASA, National Space Science Data Center. "The Moon" [cited March 10, 2003]. <http://nssdc.gsfc.nasa.gov/planetary/planets/moonpage.html>.

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