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An introduction to the moon earths only natural satellite

  1. Ancient highland material that is considered pristine is relatively rare because most highland rocks have been subjected to repeated smashing and reagglomeration by impacts and are therefore in brecciated form.
  2. This behaviour could be interpreted to show that the highly insulating layer is fairly shallow, a few metres at most. In the highlands the rocks are largely anorthosites, which are relatively rich in aluminum, calcium, and silicon.
  3. The lavas that upwelled in floods to form the maria were extremely fluid. The mare basalts, when in liquid form, were much less viscous than typical lavas on Earth; they flowed like heavy oil.

In the absence of either an atmosphere or an introduction to the moon earths only natural satellite magnetic field,… Distinctive features The Moon is a spherical rocky body, probably with a small metallic core, revolving around Earth in a slightly eccentric orbit at a mean distance of about 384,000 km 238,600 miles.

Its equatorial radius is 1,738 km 1,080 milesand its shape is slightly flattened in a such a way that it bulges a little in the direction of Earth. Its mass distribution is not uniform—the centre of mass is displaced about 2 km 1. The Moon has no global magnetic field like that of Earth, but some of its surface rocks have remanent magnetismwhich indicates one or more periods of magnetic activity in the past.

The Moon presently has very slight seismic activity and little heat flow from the interior, indications that most internal activity ceased long ago. This was followed hundreds of millions of years later by a second episode of heating—this time from internal radioactivity—which resulted in volcanic outpourings of lava. In the absence of an atmospheric shield to protect the surface from bombardment, countless bodies ranging in size from asteroid s to tiny particles have struck and cratered the Moon.

This has formed a debris layer, or regolithconsisting of rock fragments of all sizes down to the finest dust. In the ancient past the largest impacts made great basins, some of which were later partly filled by the enormous lava floods. These great dark plains, called maria singular mare [Latin: The mascons are regions where particularly dense lavas rose up from the mantle and flooded into basins. Lunar mountains, located mostly along the rims of ancient basins, are tall but not steep or sharp-peaked, because all lunar landforms have been eroded by the unending rain of impacts.

For additional orbital and physical data, see the table. Principal characteristics of the Earth-Moon system In addition to its nearness to Earththe Moon is relatively massive compared with the planet—the ratio of their masses is much larger than those of other natural satellites to the planets that they orbit. The Moon and Earth consequently exert a strong gravitational influence on each other, forming a system having distinct properties and behaviour of its own.

The table compares some salient characteristics of the two bodies.

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Planet Earth rising above the lunar horizon, an unprecedented view captured in December 1968 from the Apollo 8 spacecraft as its orbit carried it clear of the farside of the Moon. Called the barycentre, this point lies inside Earth about 4,700 km 2,900 miles from its centre. The Moon displays four main phases: New moon occurs when the Moon is between Earth and the Sun, and thus the side of the Moon that is in shadow faces Earth.

Full moon occurs when the Moon is on the opposite side of Earth from the Sun, and thus the side of the Moon that is illuminated faces Earth. First and last quarter, in which half the Moon appears illuminated, occur when the Moon is at a right angle with respect to the Sun when viewed from Earth.

Earth, as seen from the Moon, shows the same phases in opposite order; e. From the perspective of a person on Earth, a solar eclipse happens when the Moon comes between the Sun and Earth, and a lunar eclipse happens when the Moon moves into the shadow of Earth cast by the Sun.

  • These great dark plains, called maria singular mare [Latin;
  • Unlike other near-side basins, it is only partially flooded by mare lavas, which allows examination of the basin structure;
  • Eclipses of the Moon happen more often than eclipses of the Sun.

Solar eclipses occur at new moon, and lunar eclipses occur at full moon. Therefore, at most new and full moons, Earth, the Sun, and the Moon are not in a straight line. The distance between the Moon and Earth varies rather widely because an introduction to the moon earths only natural satellite the combined gravity of Earth, the Sun, and the planets. Explanation of why only one side of the Moon faces Earth. As a result of all these motions, more than 59 percent of the lunar surface can be seen at one time or another from Earth.

The Moon's phases in a synodic month, or lunation, shown in an animated time-lapse sequence of photographs taken from Earth. As the Moon orbits Earth, cycling through the familar phases of new moon through full moon and back again to new moon, its near side becomes increasingly and then decreasingly visible.

The animation makes visible the Moon's libration, an apparent to-and-fro rocking motion that allows cumulatively more than half of the lunar surface to be observed over a synodic month. Also seen is the change in the apparent size of the lunar disk as the Moon's elliptical orbit brings it alternately closer to and farther from Earth.

Eclipse of the Sun. The Moon and Earth presently orbit the barycentre in 27. Because the whole system is moving around the Sun once per year, the angle of illumination changes about one degree per day, so that the time from one full moon to the next is 29. The sidereal and synodic periods are slowly changing with time because of tidal interactions.

Consequently, the Moon is slowly receding from Earth, with the result that both the day and the month are getting longer. Extending this relationship back into the past, both periods must have been significantly shorter hundreds of millions of years ago—a hypothesis confirmed from measurements of the daily and tide-related growth rings of fossil corals.

Sunlight is always nearly horizontal at the lunar poles, which results in permanently cold and dark environments at the bottoms of deep craters. View over the lunar north pole, in a mosaic made from images collected by the Galileo spacecraft as it flew by the Moon on December 7, 1992.

Because the Moon's rotational axis is tilted only slightly toward the ecliptic plane, the terminator—the line dividing illumination from shadow—is never far from either pole, and sunlight received at the poles is always nearly horizontal. In this image, the north pole lies just within the shadowed region about a third of the way along the terminator, starting from the top left.

The long-running Chinese, Chaldean, and Mayan calendar s were attempts to reconcile these repetitive but incommensurate movements.

From the time of the Babylonian astrologers and the Greek astronomers up to the present, investigators looked for small departures from the motions predicted.

By the 18th and 19th centuries the mathematical study of lunar movements, both orbital and rotational, was advancing, driven in part by the need for precise tables of the predicted positions of celestial bodies ephemerides for navigation.

While theory developed with improved observations, many small and puzzling discrepancies continued to appear. MoonLearn about the rotation of the Moon. Both methods required significant input based on observation, but use of the latter led to great increases in the accuracy of predictions. At the same time, optical and radio observations vastly improved—retroreflectors placed on the lunar surface by Apollo astronauts allowed laser ranging of the Moon from Earth, and new techniques of radio astronomyincluding very long baseline interferometry see telescope: Very long baseline interferometrypermitted observations of celestial radio sources as the Moon occulted them.

The atmosphere Though the Moon is surrounded by a vacuum higher than is usually created in laboratories on Earth, its atmosphere is extensive and of high scientific interest. During the two-week daytime period, atoms and molecules are ejected by a variety of processes from the lunar surface, ionized by the solar windand then driven by electromagnetic effects as a collisionless plasma. The position of the Moon in its orbit determines the behaviour of the atmosphere.

The main gases naturally present are neonhydrogenheliumand argon. The argon is mostly radiogenic; i. Lunar night temperatures are low enough for the argon to condense but not the neon, hydrogen, or helium, which originate in the solar wind and remain in the atmosphere as gases unless implanted in soil particles.

The Moon, our own natural satellite

In addition to the near-surface gases and the extensive sodium -potassium cloud detected around the Moon see the section Effects of impacts and volcanism belowa small amount of dust circulates within a few metres of the lunar surface. This is believed to be suspended electrostatically. At full moon the relief disappears, replaced by the contrast between lighter and darker surfaces. Though the full moon is brilliant at night, the Moon is actually a dark object, reflecting only a few percent albedo 0.

The work culminated in a great hand-drawn lunar atlas made by observers in Berlin and Athens. This was followed by a lengthy hiatus as astronomers turned their attention beyond the Moon until the mid-20th century, when it became apparent that human travel to the Moon might eventually be possible.

In the 1950s another great atlas was compiled, this time a photographic one published in 1960 under the sponsorship of the U. Only in the 20th century did the dominance of impacts in the shaping of the lunar surface become clear. Every highland region is heavily cratered—evidence for repeated collisions with large bodies.

  1. And there are other objects that interact with Earth's orbit in strange ways.
  2. A portion of a millimetre scale is visible in the lower left corner. The properties of lunar minerals reflect the many differences between the history of the Moon and that of Earth.
  3. In other craters, which are never lit, several probes have detected frozen water from comet impacts.

The maria, on the other hand, show much less cratering and thus must be significantly younger. Mountains are mostly parts of the upthrust rims of ancient impact basins. Volcanic activity has occurred within the Moon, but the results are mostly quite different from those on Earth.

The lavas that upwelled in floods to form the maria were extremely fluid. Evidence of volcanic mountain building as has occurred on Earth is limited to a few fields of small, low domes. The mystery began to be dispelled with the flight of the Soviet space probe Luna 3 in 1959, which returned the first photographs of the far side.

In contrast to the near side, the surface displayed in the Luna 3 images consisted mostly of highlands, with only small areas of dark mare material. Later missions showed that the ancient far-side highlands are scarred by huge basins but that these basins are not filled with lava. View of the Moon never seen from Earth, predominantly the heavily cratered far side, photographed by Apollo 16 astronauts in April 1972. The near-side impact basin Mare Crisium is the large dark marking on the upper left limb; the two dark areas below it are Mare Marginis nearer Crisium and Mare Smythii.

Although the far side is well scarred with giant basins, these never filled with lava to form maria. NASA the Moon's rotationLearn about the role that Earth's gravity plays in keeping one hemisphere of the Moon facing toward the planet.

At the largest scale are the ancient basins, which extend hundreds of kilometres across. Its multiring ramparts are characteristic of the largest basins; they are accented by the partial lava flooding of low regions between the rings. Orientale Basin appears to be the youngest large impact basin on the Moon. The giant impact structure's outermost rim, the Cordillera Mountains, is 930 km 580 miles in diameter. Orientale is located on the western limb of the lunar near side.

Unlike other near-side basins, it is only partially flooded by mare lavas, which allows examination of the basin structure. During the great age of telescopic observation in the 17th—19th centuries, portrayals of the Moon usually showed south at the top because the telescopes inverted the image. East and west referred to those directions in the sky—i. For mapping purposes lunar coordinates were taken to originate near the centre of the near-side face, at the intersection of the equator and a meridian defined by the mean librations.

With the Moon considered as a world, rather than just a disk moving across the sky, east and west are interchanged.

How many moons does Earth have?

Thus, Orientale, despite its name, is located at west lunar longitudes. Smaller impact features, ranging in diameter from tens of kilometres to microscopic size, are described by the term crater. The relative ages of lunar craters are indicated by their form and structural features. Young craters have rugged profiles and are surrounded by hummocky blankets of debris, called ejecta, and long light-coloured rays made by expelled material hitting the lunar surface.

Older craters have rounded and subdued profiles, the result of continued bombardment. Copernicus crater, photographed in December 1972 by Apollo 17 astronauts above the Moon. One of the younger impact craters on the near side, Copernicus has a rugged profile, prominent central peaks, stairlike terraced walls descending to a flat floor, and a rough surrounding ejecta blanket.

The crater measures 93 km 58 miles across. At full moon its system of bright radial rays is easily seen from Earth. When a body strikes a much larger one at speeds of many kilometres per second, the available kinetic energy is enough to completely melt, even partly vaporize, the impacting body along with a small portion of its target material.

On impact, a melt sheet is thrown out, along with quantities of rubble, to form the ejecta blanket around the contact site.