Moon (Myths and Legends of the World)
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 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 , the moon was Metra, the world mother.
For some people the moon had a destructive aspect. The Aztecs of Mexico...
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Moon (Encyclopedia of Science)
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 48°F (00°C).
Formation of the Moon...
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Moon (World of Earth Science)
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 probesnd later many American probesook 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 phases synodic monthnd 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 largernd the Moon sets laterach 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 80°F to +260°F (73°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 8.86 104 inHg (3 102 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 slowedssentially 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