Moon

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A
Apollo 11
Jul 20, 1969
B
Apollo 12
Nov 19, 1969
C
Apollo 14
Feb 5, 1971
D
Apollo 15
Jul 30, 1971
E
Apollo 16
Apr 20, 1972
F
Apollo 17
Dec 11, 1972

Called Luna by the Romans, Selene and Artemis by the Greeks, and many other names in other mythologies.

The Moon, of course, has been known since prehistoric times. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once per month, the angle between the Earth, the Moon and the Sun changes; we see this as the cycle of the Moon's phases. The time between successive new moons is 29.5 days (709 hours), slightly different from the Moon's orbital period (measured against the stars) since the Earth moves a significant distance in its orbit around the Sun in that time.

Due to its size and composition, the Moon is sometimes classified as a terrestrial "planet" along with Mercury, Venus, Earth and Mars.

The Moon was first visited by the Soviet spacecraft Luna 2 in 1959. It is the only extraterrestrial body to have been visited by humans. The first landing was on July 20, 1969 (do you remember where you were?); the last was in December 1972. The Moon is also the only body from which samples have been returned to Earth. In the summer of 1994, the Moon was very extensively mapped by the little spacecraft Clementine and again in 1999 by Lunar Prospector.

The Moon is Earth's only natural satellite. The average centre-to-centre distance from the Earth to the Moon is 384,403 kilometres (238,857 miles),a which is about 30 times the diameter of the Earth. The Moon has a diameter of 3,474 kilometres (2,159 miles)[1] — slightly more than a quarter that of the Earth. This means that the volume of the Moon is only 1/50th that of Earth. The gravitational pull at its surface is about a 1/6th of Earth's. The Moon makes a complete orbit around the Earth every 27.3 days, and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the lunar phases that repeat every 29.5 days. The gravitational attraction, and the centrifugal forces generated by the rotation of the Moon and Earth around a common axis, the barycentre, is largely responsible for the tides on Earth. The energy dissipated in generating tides is directly responsible for the reduction in potential energy in the Moon-Earth orbit around the barycentre, resulting in a 3.8 cm yearly increase in the distance between the two bodies.[2] The Moon will continue to move slowly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will stabilise.

The Moon is the only celestial body that humans have travelled to and landed on. The first artificial object to escape Earth's gravity and pass near the Moon was the Soviet Union's Luna 1, the first artificial object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9 and the first unmanned vehicle to orbit the Moon was Luna 10, both in 1966.[1] The U.S. Apollo program has achieved the first (and only) manned missions to date, resulting in six landings between 1969 and 1972. Human exploration of the Moon ceased with the conclusion of the Apollo program, although as of 2007, several countries have announced plans to send either people or robotic spacecraft to the Moon. On 4 December 2006, NASA outlined plans for a permanent base on the Moon as part of preparation for a voyage to Mars. Construction of the base is scheduled to take about five years, with the first preliminary missions by 2020.[3]

The Moon has no formal English name, although it is occasionally called Luna (Latin for "moon") to distinguish it from the generic "moon" (referring to any of the various natural satellites of other planets). Its astronomical symbol is a crescent (☽). The related adjective for the Moon is lunar (from the Latin root), or the adjectival prefix seleno- or suffix -selene (as in the Greek deity Selene). The word moon is a Germanic word, related to Latin mensis; it comes ultimately from the PIE root me-, also represented in "measure"[4] (time), with reminders of its importance in measuring time in words derived from it like Monday, month and menstrual.

Two sides of the Moon

The Moon is in synchronous rotation, meaning that it keeps nearly the same face turned away from Earth at all times. Early in the Moon's history, its rotation slowed and became locked in this configuration as a result of frictional effects associated with tidal deformations caused by the Earth.[6] Nevertheless, small variations resulting from the eccentricity of the lunar orbit, termed librations, allow about 59 percent of the lunar surface to be viewed from Earth.

 Moon rocks

Moon rocks fall into two main categories, based on whether they underlie the lunar highlands (terrae) or the maria. The lunar highlands rocks are composed of three suites: the ferroan anorthosite suite, the magnesian suite, and the alkali suite (some consider the alkali suite to be a subset of the mg-suite). The ferroan anorthosite suite rocks are composed almost exclusively of the mineral anorthite (a calic plagioclase feldspar), and are believed to represent plagioclase flotation cumulates of the lunar magma ocean. The ferroan anorthosites have been dated using radiometric methods to have formed about 4.4 billion years ago.[36][37]

The mg- and alkali-suite rocks are predominantly mafic plutonic rocks. Typical rocks are dunites, troctolites, gabbros, alkali anorthosites, and more rarely, granite. In contrast to the ferroan anorthosite suite, these rocks all have relatively high Mg/Fe ratios in their mafic minerals. In general, these rocks represent intrusions into the already-formed highlands crust (though a few rare samples appear to represent extrusive lavas), and they have been dated to have formed about 4.4–3.9 billion years ago. Many of these rocks have high abundances of, or are genetically related to, the geochemical component KREEP.

The lunar maria consist entirely of mare basalts. While similar to terrestrial basalts, they have much higher abundances of iron, are completely lacking in hydrous alteration products, and have a large range of titanium abundances.

The Moon is 384,403 kilometers (238,857 miles) distant from the Earth. Its diameter is 3,476 kilometers (2,160 miles). Both the rotation of the Moon and its revolution around Earth takes 27 days, 7 hours, and 43 minutes. This synchronous rotation is caused by an unsymmetrical distribution of mass in the Moon, which has allowed Earth's gravity to keep one lunar hemisphere permanently turned toward Earth. Optical librations have been observed telescopically since the mid-17th century. Very small but real librations (maximum about 0°.04) are caused by the effect of the Sun's gravity and the eccentricity of Earth's orbit, perturbing the Moon's orbit and allowing cyclical preponderances of torque in both east-west and north-south directions.

Four nuclear powered seismic stations were installed during the Apollo project to collect seismic data about the interior of the Moon. There is only residual tectonic activity due to cooling and tidal forcing, but other moonquakes have been caused by meteor impacts and artificial means, such as deliberately crashing the Lunar Module into the moon. The results have shown the Moon to have a crust 60 kilometers (37 miles) thick at the center of the near side. If this crust is uniform over the Moon, it would constitute about 10% of the Moon's volume as compared to the less than 1% on Earth. The seismic determinations of a crust and mantle on the Moon indicate a layered planet with differentiation by igneous processes. There is no evidence for an iron-rich core unless it were a small one. Seismic information has influenced theories about the formation and evolution of the Moon.

The Moon was heavily bombarded early in its history, which caused many of the original rocks of the ancient crust to be thoroughly mixed, melted, buried, or obliterated. Meteoritic impacts brought a variety of "exotic" rocks to the Moon so that samples obtained from only 9 locations produced many different rock types for study. The impacts also exposed Moon rocks of great depth and distributed their fragments laterally away from their places of origin, making them more accessible. The underlying crust was also thinned and cracked, allowing molten basalt from the interior to reach the surface. Because the Moon has neither an atmosphere nor any water, the components in the soils do not weather chemically as they would on Earth. Rocks more than 4 billion years old still exist there, yielding information about the early history of the solar system that is unavailable on Earth. Geological activity on the Moon consists of occasional large impacts and the continued formation of the regolith. It is thus considered geologically dead. With such an active early history of bombardment and a relatively abrupt end of heavy impact activity, the Moon is considered fossilized in time.

The Apollo and Luna missions returned 382 kilograms (840 pounds) of rock and soil from which three major surface materials have been studied: the regolith, the maria, and the terrae. Micrometeorite bombardment has thoroughly pulverized the surface rocks into a fine-grained debris called the regolith. The regolith, or lunar soil, is unconsolidated mineral grains, rock fragments, and combinations of these which have been welded by impact-generated glass. It is found over the entire Moon, with the exception of steep crater and valley walls. It is 2 to 8 meters (7 to 26 feet) thick on the maria and may exceed 15 meters (49 feet) on the terrae, depending on how long the bedrock underneath it has been exposed to meteoritic bombardment.

The dark, relatively lightly cratered maria cover about 16% of the lunar surface and is concentrated on the nearside of the Moon, mostly within impact basins. This concentration may be explained by the fact that the Moon's center of mass is offset from its geometric center by about 2 kilometers (1.2 miles) in the direction of Earth, probably because the crust is thicker on the farside. It is possible, therefore, that basalt magmas rising from the interior reached the surface easily on the nearside, but encountered difficulty on the farside. Mare rocks are basalt and most date from 3.8 to 3.1 billion years. Some fragments in highland breccias date to 4.3 billion years and high resolution photographs suggest some mare flows actually embay young craters and may thus be as young as 1 billion years. The maria average only a few hundred meters in thickness but are so massive they frequently deformed the crust underneath them which created fault-like depressions and raised ridges.

The relatively bright, heavily cratered highlands are called terrae. The craters and basins in the highlands are formed by meteorite impact and are thus older than the maria, having accumulated more craters. The dominant rock type in this region contain high contents of plagioclase feldspar (a mineral rich in calcium and aluminum) and are a mixture of crustal fragments brecciated by meteorite impacts. Most terrae breccias are composed of still older breccia fragments. Other terrae samples are fine-grained crystalline rocks formed by shock melting due to the high pressures of an impact event. Nearly all of the highland breccias and impact melts formed about 4.0 to 3.8 billion years ago. The intense bombardment began 4.6 billion years ago, which is the estimated time of the Moon's origin.

The moon is about 238,900 miles (384,000 km) from Earth on average. At its closest approach (the lunar perigee) the moon is 221,460 miles (356,410 km) from the Earth. At its farthest approach (its apogee) the moon is 252,700 miles (406,700 km) from the Earth.

The moon revolves around the Earth in about one month (27 days 8 hours). It rotates around its own axis in the same amount of time. The same side of the moon always faces the Earth; it is in a synchronous rotation with the Earth.

The Moon's orbit is expanding over time as it slows down (the Earth is also slowing down as it loses energy). For example, a billion years ago, the Moon was much closer to the Earth (roughly 200,000 kilometers) and took only 20 days to orbit the Earth. Also, one Earth 'day' was about 18 hours long (instead of our 24 hour day). The tides on Earth were also much stronger since the moon was closer to the Earth.

Future Missions

* Chandrayaan-1 - ISRO (India) Lunar Orbiter Mission (2007)
* Chang'e 1 - CAST (China) Lunar Orbiter Mission (2007)
* SELENE - JAXA (Japan) Lunar Orbiter Mission (2007)
* Lunar Reconnaissance Orbiter - NASA Lunar Orbiter Mission (2008)
* Moonrise - NASA New Frontiers sample return mission under study

Exploration of the moon began in 1959 when the unmanned Luna 2 landed on its surface. Luna 2 was closely followed by Luna 3 in late 1959, which obtained the first images of the occluded far side of the moon, and the first people to land on the Moon came aboard Apollo 11 on that historic night in 1969.

New Moon

Waxing Crescent

First Quarter

Waxing Gibbous

Full Moon

Waning Gibbous

Last Quarter

Waning Crescent

Jun 29, 2:00 PM ET

This weekend's full moon hangs lower in the sky than any other full moon of 2007, according to NASA, and it's a good time to be fooled.
 

When low on the horizon, the Moon can appear to be larger than when it's higher in the sky. It's all an illusion, scientists say, and it does not involve any enlarging effects of the atmosphere. Rather, it's all in your mind.

Here's how it works:

Our brains think things on the horizon are farther away than stuff overhead, because we're used to seeing overhead clouds that are close compared to those on the horizon. In the mind's eye, the sky is a flattened dome.

With this dome as a reference, we expect something on the horizon (such as the moon) to be father, and because it is actually no farther than when overhead, our brains goof and imagine that it is larger.

Skeptical? You can test this from home.

When the moon first rises, hold something small like the eraser of a pencil at arms length and compare its size to the moon on the horizon. Do the same a couple hours later when the moon is higher. Or try this: Take a picture of the moon in both positions, then cut, paste and compare. Another trick: Make a tube from rolled-up paper so the opening is just slightly larger than the moon when it rises. Tape the tube so the size stays fixed, then check later to see if the moon has changed sizes.

Officially, the moon will be full Saturday June 30 at 9:49 a.m. ET. Of course, you'll want to do your looking in the evening. Local moonrise times are available from the U.S. Naval Observatory. Keep in mind that mountains and buildings can dramatically alter your actual local moonrise time.

The big-moon-rising effect will be evident Friday, Saturday and Sunday. On each evening, the moon will appear nearly full. Interestingly, the moon is never fully full from our point of view, but that's another story.

While you're out, check out Venus and Saturn, which are snuggling close together in the western sky as darkness falls.

So why is one full moon lower in the sky than another? The moon's orbit around Earth is tilted 5 degrees compared to the plane of Earth's travels around the Sun, and Earth itself is tilted on its rotational axis. All this accounts for the lunar phases, and it also means the moon's path through our sky can be higher or lower depending on the angles on any given night.

The complex orbit of the Earth-moon system is constantly evolving, too. Right now, the moon is moving away from us by more than 1.5 inches every year.