The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, the largest among planetary satellites relative to the size of the planet that it orbits; the Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known. The Moon is thought to have formed not long after Earth; the most accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, thus always shows the same side to Earth, the near side; the near side is marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. After the Sun, the Moon is the second-brightest visible celestial object in Earth's sky, its surface is dark, although compared to the night sky it appears bright, with a reflectance just higher than that of worn asphalt.
Its gravitational influence produces the ocean tides, body tides, the slight lengthening of the day. The Moon's average orbital distance is 1.28 light-seconds. This is about thirty times the diameter of Earth; the Moon's apparent size in the sky is the same as that of the Sun, since the star is about 400 times the lunar distance and diameter. Therefore, the Moon covers the Sun nearly during a total solar eclipse; this matching of apparent visual size will not continue in the far future because the Moon's distance from Earth is increasing. The Moon was first reached in September 1959 by an unmanned spacecraft; the United States' NASA Apollo program achieved the only manned lunar missions to date, beginning with the first manned orbital mission by Apollo 8 in 1968, six manned landings between 1969 and 1972, with the first being Apollo 11. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, the Moon's history. Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft.
Both the Moon's natural prominence in the earthly sky and its regular cycle of phases as seen from Earth have provided cultural references and influences for human societies and cultures since time immemorial. Such cultural influences can be found in language, lunar calendar systems and mythology; the usual English proper name for Earth's natural satellite is "the Moon", which in nonscientific texts is not capitalized. The noun moon is derived from Old English mōna, which stems from Proto-Germanic *mēnô, which comes from Proto-Indo-European *mḗh₁n̥s "moon", "month", which comes from the Proto-Indo-European root *meh₁- "to measure", the month being the ancient unit of time measured by the Moon; the name "Luna" is used. In literature science fiction, "Luna" is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of Earth's moon; the modern English adjective pertaining to the Moon is lunar, derived from the Latin word for the Moon, luna. The adjective selenic is so used to refer to the Moon that this meaning is not recorded in most major dictionaries.
It is derived from the Ancient Greek word for the Moon, σελήνη, from, however derived the prefix "seleno-", as in selenography, the study of the physical features of the Moon, as well as the element name selenium. Both the Greek goddess Selene and the Roman goddess Diana were alternatively called Cynthia; the names Luna and Selene are reflected in terminology for lunar orbits in words such as apolune and selenocentric. The name Diana comes from the Proto-Indo-European *diw-yo, "heavenly", which comes from the PIE root *dyeu- "to shine," which in many derivatives means "sky and god" and is the origin of Latin dies, "day"; the Moon formed 4.51 billion years ago, some 60 million years after the origin of the Solar System. Several forming mechanisms have been proposed, including the fission of the Moon from Earth's crust through centrifugal force, the gravitational capture of a pre-formed Moon, the co-formation of Earth and the Moon together in the primordial accretion disk; these hypotheses cannot account for the high angular momentum of the Earth–Moon system.
The prevailing hypothesis is that the Earth–Moon system formed after an impact of a Mars-sized body with the proto-Earth. The impact blasted material into Earth's orbit and the material accreted and formed the Moon; the Moon's far side has a crust, 30 mi thicker than that of the near side. This is thought to be; this hypothesis, although not perfect best explains the evidence. Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at Kona, the giant impact hypothesis emerged as the most consensual theory. Before the conference, there were parti
Magnetic field of the Moon
The magnetic field of the Moon is weak in comparison to that of the Earth. Other major differences are that the Moon does not have a dipolar magnetic field and the varying magnetization, present is entirely crustal in origin. One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. An analysis of magnetized Moon rocks brought to Earth by Apollo astronauts showed that the Moon must have had a strong magnetic field at least 4.25 billion years ago, which fell to 20 uT level in the 3.6 - 3.1 billion years BP period. The small size of the lunar core, however, is a potential obstacle to promoting that hypothesis to the status of theory. Alternatively, it is possible that on an airless body such as the Moon, transient magnetic fields could be generated during large impact events. In support of this, it has been noted that the largest crustal magnetizations appear to be located near the antipodes of the giant impact basins, it has been proposed that such a phenomenon could result from the free expansion of an impact-generated plasma cloud around the Moon in the presence of an ambient magnetic field.
For example, the Chandrayaan-1 spacecraft mapped a "mini-magnetosphere" at the Crisium antipode on the Moon's far side, using its Sub-keV Atom Reflecting Analyzer instrument. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. There is growing evidence that fine particles of moondust might float, ejected from the lunar surface by electrostatic repulsion; this could create a temporary nighttime "atmosphere" of dust. The moondust atmosphere might gather itself into a sort of diaphanous wind. Drawn by differences in global charge accumulation, floating dust would fly from the negative nightside to the weakly negative dayside; this "dust storm" effect would be strongest at the Moon's terminator. Much of these details are still speculative, but the Lunar Prospector spacecraft detected changes in the lunar nightside voltage during magnetotail crossings, jumping from -200 V to -1000 V.
Further characterization was done by the Lunar Atmosphere and Dust Environment Explorer orbiter in late 2013. The plasma sheet is a dynamic structure, in a constant state of motion, so as the Moon orbits through the magnetotail the plasma sheet can sweep across it many times with encounters lasting anywhere from minutes to hours or days. In the Space Odyssey series by Arthur C. Clarke, a monolith is found on the Moon near the crater Tycho by its unnaturally powerful magnetic field and named Tycho Magnetic Anomaly 1. Gravity field of the Moon Topography of the Moon
A lunar eclipse occurs when the Moon passes directly behind Earth and into its shadow. This can occur only when the Sun and Moon are or closely aligned, with Earth between the other two. A lunar eclipse can occur only on the night of a full moon; the type and length of a lunar eclipse depend on the Moon's proximity to either node of its orbit. During a total lunar eclipse, Earth blocks direct sunlight from reaching the Moon; the only light reflected from the lunar surface has been refracted by Earth's atmosphere. This light appears reddish for the same reason that a sunset or sunrise does: the Rayleigh scattering of bluer light. Due to this reddish color, a eclipsed Moon is sometimes called a blood moon. Unlike a solar eclipse, which can only be viewed from a small area of the world, a lunar eclipse may be viewed from anywhere on the night side of Earth. A total lunar eclipse can last up to nearly 2 hours, while a total solar eclipse lasts only up to a few minutes at any given place, due to the smaller size of the Moon's shadow.
Unlike solar eclipses, lunar eclipses are safe to view without any eye protection or special precautions, as they are dimmer than the full Moon. For the date of the next eclipse, see the section Recent and forthcoming lunar eclipses. Earth's shadow can be divided into two distinctive parts: penumbra. Earth occludes direct solar radiation within the umbra, the central region of the shadow. However, since the Sun's diameter appears about one-quarter of Earth's in the lunar sky, the planet only blocks direct sunlight within the penumbra, the outer portion of the shadow. A penumbral lunar eclipse occurs; the penumbra causes a subtle dimming of the lunar surface. A special type of penumbral eclipse is a total penumbral lunar eclipse, during which the Moon lies within Earth's penumbra. Total penumbral eclipses are rare, when these occur, the portion of the Moon closest to the umbra may appear darker than the rest of the lunar disk. A partial lunar eclipse occurs when only a portion of the Moon enters Earth's umbra, while a total lunar eclipse occurs when the entire Moon enters the planet's umbra.
The Moon's average orbital speed is about 1.03 km/s, or a little more than its diameter per hour, so totality may last up to nearly 107 minutes. The total time between the first and the last contacts of the Moon's limb with Earth's shadow is much longer and could last up to four hours; the relative distance of the Moon from Earth at the time of an eclipse can affect the eclipse's duration. In particular, when the Moon is near apogee, the farthest point from Earth in its orbit, its orbital speed is the slowest; the diameter of Earth's umbra does not decrease appreciably within the changes in the Moon's orbital distance. Thus, the concurrence of a eclipsed Moon near apogee will lengthen the duration of totality. A central lunar eclipse is a total lunar eclipse during which the Moon passes through the centre of Earth's shadow, contacting the antisolar point; this type of lunar eclipse is rare. A selenelion or selenehelion occurs when both the Sun and an eclipsed Moon can be observed at the same time.
This can occur only just before sunset or just after sunrise, when both bodies will appear just above the horizon at nearly opposite points in the sky. This arrangement has led to the phenomenon being called a horizontal eclipse. A number of high ridges undergoing sunrise or sunset can view it. Although the Moon is in Earth's umbra, both the Sun and an eclipsed Moon can be seen because atmospheric refraction causes each body to appear higher in the sky than their true geometric positions; the timing of total lunar eclipses are determined by its contacts: P1: Beginning of the penumbral eclipse. Earth's penumbra touches the Moon's outer limb. U1: Beginning of the partial eclipse. Earth's umbra touches the Moon's outer limb. U2: Beginning of the total eclipse; the Moon's surface is within Earth's umbra. Greatest eclipse: The peak stage of the total eclipse; the Moon is at its closest to the center of Earth's umbra. U3: End of the total eclipse; the Moon's outer limb exits Earth's umbra. U4: End of the partial eclipse.
Earth's umbra leaves the Moon's surface. P4: End of the penumbral eclipse. Earth's penumbra no longer makes contact with the Moon; the following scale was devised by André Danjon for rating the overall darkness of lunar eclipses: L=0: Very dark eclipse. Moon invisible at mid-totality. L=1: Dark eclipse, gray or brownish in coloration. Details distinguishable only with difficulty. L=2: Deep red or rust-colored eclipse. Dark central shadow, while outer edge of umbra is bright. L=3: Brick-red eclipse. Umbral shadow has a bright or yellow rim. L=4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a bright rim. There is confusion between a solar eclipse and a lunar eclipse. While both involve interactions between the Sun and the Moon, they are different in their interactions; the Moon does not darken as it passes through the umbra because of the refraction of sunlight by Earth's atmosphere into the shadow cone. The reddish coloration arises because sunlight reaching the Moon must pass through a long and dense layer of Earth's atmosphere, where it is scattered.
Shorter wavelengths are more to be scattered by the air molecules and small particles.
In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the unaided eye, except when silhouetted during a solar eclipse. Daylight outshines the earthlight; the actual phase is a thin crescent. The original meaning of the term new moon, still sometimes used in non-astronomical contexts, was the first visible crescent of the Moon, after conjunction with the Sun; this crescent moon is visible when low above the western horizon shortly after sunset and before moonset. A lunation or synodic month is the average time from one new moon to the next. In the J2000.0 epoch, the average length of a lunation is 29.530588 days. However, the length of any one synodic month can vary from 29.26 to 29.80 days due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit. In a lunar calendar, each month corresponds to a lunation; each lunar cycle can be assigned a unique lunation number to identify it.
The length of a lunation is about 29.53 days. Its precise duration is linked to many phenomena in nature, such as the variation between spring and neap tides. An approximate formula to compute the mean moments of new moon for successive months is: d = 5.597661 + 29.5305888610 × N + × N 2 where N is an integer, starting with 0 for the first new moon in the year 2000, and, incremented by 1 for each successive synodic month. To obtain this moment expressed in Universal Time, add the result of following approximate correction to the result d obtained above: − 0.000739 − × N 2 daysPeriodic perturbations change the time of true conjunction from these mean values. For all new moons between 1601 and 2401, the maximum difference is 0.592 days = 14h13m in either direction. The duration of a lunation varies in this period between 29.272 and 29.833 days, i.e. −0.259d = 6h12m shorter, or +0.302d = 7h15m longer than average. This range is smaller than the difference between mean and true conjunction, because during one lunation the periodic terms cannot all change to their maximum opposite value.
See the article on the full moon cycle for a simple method to compute the moment of new moon more accurately. The long-term error of the formula is approximately: 1 cy2 seconds in TT, 11 cy2 seconds in UT The moment of mean conjunction can be computed from an expression for the mean ecliptical longitude of the Moon minus the mean ecliptical longitude of the Sun. Jean Meeus gave formulae to compute this in his Astronomical Formulae for Calculators based on the ephemerides of Brown and Newcomb; these are now outdated: Chapront et al. published improved parameters. Meeus's formula uses a fractional variable to allow computation of the four main phases, uses a second variable for the secular terms. For the convenience of the reader, the formula given above is based on Chapront's latest parameters and expressed with a single integer variable, the following additional terms have been added: constant term: Like Meeus, apply the constant terms of the aberration of light for the Sun's motion and light-time correction for the Moon to obtain the apparent difference in ecliptical longitudes:Sun: +20.496" Moon: −0.704" Correction in conjunction: −0.000451 daysFor UT: at 1 January 2000, ΔT was +63.83 s.
The term includes a tidal contribution of 0.5×. The most current estimate from Lunar Laser Ranging for the acceleration is:"/cy2. Therefore, the new quadratic term of D is = -6.8498"T2. Indeed, the polynomial provided by Chapront et alii provides the same value; this translates to a correction of +14.622×10−12N2 days to the time of conjunction. For UT: analysis of historical observations shows that ΔT has a long-term increase of +31 s/cy2. Converted to days and lunations, the correction from ET to UT becomes:−235×10−12N2 days; the theoretical tidal contribution to ΔT is about +42 s/cy2 the smaller observed value is thought to be due to changes in the shape of the Earth. Because the discrepancy is not explained, uncertainty of our prediction of UT may be as large as the difference between these values: 11 s/cy2; the error in the position of the Moon itself is only maybe 0.5"/cy2, or (because the apparent mean angular velocit
Moonlight consists of sunlight reflected from the parts of the Moon's surface where the Sun's light strikes. The intensity of moonlight varies depending on its phase, but the full Moon provides only about 0.05–0.1 lux illumination. When the full Moon is at perigee and viewed around upper culmination from the tropics, the illuminance can reach up to 0.32 lux. From Earth, the apparent magnitude of the full Moon is only about 1⁄380,000 that of the Sun; the color of moonlight around full Moon, appears bluish to the human eye compared to most artificial light sources due to the Purkinje effect. Moonlight is not tinted blue, although moonlight is referred to as "silvery", it has no inherent silvery quality; the Moon's albedo is 0.136, meaning only 13.6% of incident sunlight is reflected from the lunar surface. Moonlight hampers astronomical viewing, so astronomers avoid observing sessions around full Moon, it takes 1.26 seconds for moonlight to reach Earth's surface. In folklore, moonlight sometimes has a harmful influence.
For example, sleeping in the light of a full Moon on certain nights was said to transform a person into a werewolf. The light of the Moon was thought to worsen the symptoms of lunatics, to sleep in moonlight could make one blind, or mad. Nyctalopia was thought to be caused by sleeping in moonlight in the tropics. "Moon blindness" is a name for equine recurrent uveitis. Moonlight is no longer thought of as the cause. In the 16th century, moonmilk, a soft white limestone precipitate found in caves, was thought to be caused by the rays of the Moon. In 2008 Katie Paterson produced, it consists of 289 lightbulbs coated to produce a similar spectrum to the light of the full Moon. Airglow Daylight Diffuse reflection Earthlight Lunar effect Scotobiology Starlight Night in paintings Night in paintings Phases of the Moon at USNO Strange Moonlight at Science@NASA Moonlight Brightness at LunarLight Photography
In Vedic timekeeping, a tithi is a lunar day, or the time it takes for the longitudinal angle between the Moon and the Sun to increase by 12°. In other words, a tithi is a time-duration between the consecutive epochs that correspond to when the longitudinal-angle between sun and moon is an integer multiple of 12°. Tithis begin at varying times of day and vary in duration from 19 to 26 hours. A Hindu muhurta can be represented in five attributes of Hindu astronomy namely, vara the weekday, nakshatra the Moon's asterism, yoga the angular relationship between Sun and Moon and karana half of tithi. Tithi plays an important role along with nakshatra in Hindus' daily as well as special activities in selecting the muhurta. There are auspicious tithis as well as inauspicious tithis, each considered more propitious for some purposes than for other. There are 30 tithis in each lunar month, named as: Panchangam In Telugu With Tithi The Vaisnava Calendar The Hindu Lunisolar Calendar iPhone app Free Hindu Panchang பஞ்சாங்கம் google app
Topography of the Moon
The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, including data obtained during the Clementine mission. The most visible topographic feature is the giant far side South Pole-Aitken basin, which possesses the lowest elevations of the Moon; the highest elevations are found just to the north-east of this basin, it has been suggested that this area might represent thick ejecta deposits that were emplaced during an oblique South Pole-Aitken basin impact event. Other large impact basins, such as the maria Imbrium, Crisium and Orientale possess regionally low elevations and elevated rims. Another distinguishing feature of the Moon's shape is that the elevations are on average about 1.9 km higher on the far side than the near side. If it is assumed that the crust is in isostatic equilibrium, that the density of the crust is everywhere the same the higher elevations would be associated with a thicker crust. Using gravity and seismic data, the crust is thought to be on average about 50 ± 15 km thick, with the far-side crust being on average thicker than the near side by about 15 km.
Gravitation of the Moon