Venus

This article is about the planet. For other uses, see Venus(disambiguation).

Venus is the second planet from the Sun, orbiting it every224.7 Earth days.[10] It has no natural satellite. It is namedafter the Roman goddess of love and beauty. After theMoon, it is the brightest natural object in the night sky,reaching an apparent magnitude of 4.6, bright enoughto cast shadows.[11] Because Venus is an inferior planetfrom Earth, it never appears to venture far from the Sun:its elongation reaches a maximum of 47.8.Venus is a terrestrial planet and is sometimes calledEarths sister planet because of their similar size, mass,proximity to the Sun and bulk composition. It is radi-cally dierent from Earth in other respects. It has thedensest atmosphere of the four terrestrial planets, consist-ing of more than 96% carbon dioxide. The atmosphericpressure at the planets surface is 92 times that of Earths.With a mean surface temperature of 735 K (462 C; 863F), Venus is by far the hottest planet in the Solar Sys-tem, even though Mercury is closer to the Sun. Venushas no carbon cycle that puts carbon into rock, nor does itseem to have any organic life to absorb carbon in biomass.Venus is shrouded by an opaque layer of highly reectiveclouds of sulfuric acid, preventing its surface from beingseen from space in visible light. It may have possessedoceans in the past,[12][13] but these would have vaporizedas the temperature rose due to a runaway greenhouse ef-fect.[14] The water has most probably photodissociated,and, because of the lack of a planetary magnetic eld, thefree hydrogen has been swept into interplanetary space bythe solar wind.[15] Venus surface is a dry desertscape in-terspersed with slab-like rocks and periodically refreshedby volcanism.

1 Physical characteristics

Venus is one of the four terrestrial planets in the SolarSystem, meaning that, like Earth, it is a rocky body. Insize and mass, it is similar to Earth, and is often describedas Earths sister or twin.[16] The diameter of Venus is12,092 km (only 650 km less than Earths) and its massis 81.5% of Earths. Conditions on the Venusian surfacedier radically from those on Earth, owing to its densecarbon dioxide atmosphere. The mass of the atmosphereof Venus is 96.5% carbon dioxide, with most of the re-maining 3.5% being nitrogen.[17]

Size comparison of Mercury, Venus, Earth and the Moon, Mars,and Ceres on the far right. This may not be exactly to scale,because the visual disc of Venus with its atmosphere makes itlook bigger than its solid-body diameter.

Size comparison with Earth.

1.1 Geography

The Venusian surface was a subject of speculation un-til some of its secrets were revealed by planetary sci-ence in the 20th century. It was nally mapped in de-tail by Project Magellan in 199091. The ground showsevidence of extensive volcanism, and the sulfur in theatmosphere may indicate there have been some recenteruptions.[18][19]

About 80% of the Venusian surface is covered by smooth,volcanic plains, consisting of 70% plains with wrinkleridges and 10% smooth or lobate plains.[20] Two highlandcontinents make up the rest of its surface area, one ly-ing in the planets northern hemisphere and the other justsouth of the equator. The northern continent is calledIshtar Terra, after Ishtar, the Babylonian goddess of love,and is about the size of Australia. Maxwell Montes, thehighest mountain on Venus, lies on Ishtar Terra. Its peakis 11 km above the Venusian average surface elevation.The southern continent is called Aphrodite Terra, afterthe Greek goddess of love, and is the larger of the twohighland regions at roughly the size of South America.A network of fractures and faults covers much of thisarea.[21]

1

2 1 PHYSICAL CHARACTERISTICS

The absence of evidence of lava ow accompanying anyof the visible caldera remains an enigma. The planet hasfew impact craters, demonstrating the surface is relativelyyoung, approximately 300600 million years old.[22][23]In addition to the impact craters, mountains, and val-leys commonly found on rocky planets, Venus has someunique surface features. Among these are at-topped vol-canic features called "farra", which look somewhat likepancakes and range in size from 20 to 50 km across,and from 100 to 1,000 m high; radial, star-like frac-ture systems called novae"; features with both radial andconcentric fractures resembling spider webs, known as"arachnoids"; and coronae, circular rings of fracturessometimes surrounded by a depression. These featuresare volcanic in origin.[24]

Most Venusian surface features are named after histori-cal and mythological women.[25] Exceptions are MaxwellMontes, named after James Clerk Maxwell, and high-land regions Alpha Regio, Beta Regio and Ovda Regio.The former three features were named before the cur-rent system was adopted by the International Astronom-ical Union, the body that oversees planetary nomencla-ture.[26]

The longitudes of physical features on Venus are ex-pressed relative to its prime meridian. The originalprime meridian passed through the radar-bright spot atthe center of the oval feature Eve, located south of AlphaRegio.[27] After the Venera missions were completed, theprime meridian was redened to pass through the centralpeak in the crater Ariadne.[28][29]

1.2 Surface geologyMain article: Geology of VenusMuch of the Venusian surface appears to have been

Maat Mons with a vertical exaggeration of 22.5

shaped by volcanic activity. Venus has several timesas many volcanoes as Earth, and it possesses 167 largevolcanoes that are over 100 km across. The only vol-canic complex of this size on Earth is the Big Island of

Hawaii.[24] This is not because Venus is more volcanicallyactive than Earth, but because its crust is older. Earthsoceanic crust is continually recycled by subduction at theboundaries of tectonic plates, and has an average age ofabout 100 million years,[30] whereas the Venusian surfaceis estimated to be 300600 million years old.[22][24]

Several lines of evidence point to ongoing volcanic ac-tivity on Venus. During the Soviet Venera program, theVenera 11 and Venera 12 probes detected a constantstream of lightning, and Venera 12 recorded a power-ful clap of thunder soon after it landed. The EuropeanSpace Agency's Venus Express recorded abundant light-ning in the high atmosphere.[31] Although rainfall drivesthunderstorms on Earth, there is no rainfall on the sur-face of Venus (though sulfuric acid rain falls in the upperatmosphere, then evaporates around 25 km above the sur-face). One possibility is that ash from a volcanic eruptionwas generating the lightning. Another piece of evidencecomes from measurements of sulfur dioxide concentra-tions in the atmosphere, which dropped by a factor of10 between 1978 and 1986. This may mean the levelshad earlier been boosted by a large volcanic eruption.[32]Almost a thousand impact craters on Venus are evenlydistributed across its surface. On other cratered bod-ies, such as Earth and the Moon, craters show a rangeof states of degradation. On the Moon, degradation iscaused by subsequent impacts, whereas on Earth it iscaused by wind and rain erosion. On Venus, about 85%of the craters are in pristine condition. The number ofcraters, together with their well-preserved condition, in-dicates the planet underwent a global resurfacing eventabout 300600 million years ago,[22][23] followed by a de-cay in volcanism.[33] Whereas Earths crust is in continu-ous motion, Venus is thought to be unable to sustain sucha process. Without plate tectonics to dissipate heat fromits mantle, Venus instead undergoes a cyclical process inwhich mantle temperatures rise until they reach a criti-cal level that weakens the crust. Then, over a period ofabout 100 million years, subduction occurs on an enor-mous scale, completely recycling the crust.[24] In March2014, the rst direct evidence for ongoing volcanism waslocated, in the form of infrared ashes over the riftzone Ganiki Chasma, near the shield volcanoMaatMons.These ashes, ranging from 40 to 320 C above the am-bient, are believed to be either hot gases or lava releasedfrom volcanic eruptions.[34]

Venusian craters range from 3 km to 280 km in diameter.No craters are smaller than 3 km, because of the eectsof the dense atmosphere on incoming objects. Objectswith less than a certain kinetic energy are slowed downso much by the atmosphere that they do not create an im-pact crater.[35] Incoming projectiles less than 50 metresin diameter will fragment and burn up in the atmospherebefore reaching the ground.[36]

1.4 Atmosphere and climate 3

The internal structure of Venus the crust (outer layer), the man-tle (middle layer) and the core (yellow inner layer)

1.3 Internal structure

Without seismic data or knowledge of its moment of in-ertia, little direct information is available about the inter-nal structure and geochemistry of Venus.[37] The similar-ity in size and density between Venus and Earth suggeststhey share a similar internal structure: a core, mantle, andcrust. Like that of Earth, the Venusian core is at leastpartially liquid because the two planets have been cool-ing at about the same rate.[38] The slightly smaller sizeof Venus suggests pressures are signicantly lower in itsdeep interior than Earth. The principal dierence be-tween the two planets is the lack of evidence for plate tec-tonics on Venus, possibly because its crust is too strong tosubduct without water to make it less viscous. This resultsin reduced heat loss from the planet, preventing it fromcooling and providing a likely explanation for its lack ofan internally generated magnetic eld.[39] Instead, Venusmay lose its internal heat in periodic major resurfacingevents.[22]

1.4 Atmosphere and climate

Cloud structure in the Venusian atmosphere in 1979,revealed by observations in the ultraviolet band byPioneer Venus Orbiter

Global radar view of Venus (without the clouds) fromthe Magellan imaging between 1990 and 1994

Impact craters on the surface of Venus (image recon-structed from radar data)Main article: Atmosphere of Venus

Venus has an extremely dense atmosphere, which con-sists mainly of carbon dioxide and a small amount ofnitrogen. The atmospheric mass is 93 times that ofEarths atmosphere, whereas the pressure at the planetssurface is about 92 times that at Earths surfacea pres-

4 1 PHYSICAL CHARACTERISTICS

sure equivalent to that at a depth of nearly 1 kilometre un-der Earths oceans. The density at the surface is 65 kg/m3,6.5% that of water or 50 times as dense as Earths atmo-sphere at 20 C at sea level. The CO2-rich atmosphere,along with thick clouds of sulfur dioxide, generates thestrongest greenhouse eect in the Solar System, creatingsurface temperatures of at least 735 K (462 C).[10][40]This makes the Venusian surface hotter than Mercury's,which has a minimum surface temperature of 55 K (220C) and maximum surface temperature of 695 K (420C),[41] even though Venus is nearly twice Mercurys dis-tance from the Sun and thus receives only 25% of Mer-curys solar irradiance. The surface of Venus is oftendescribed as hellish.[42] This temperature is higher thantemperatures used to achieve sterilization.Studies have suggested that billions of years ago theVenu-sian atmosphere was much more like Earths than it isnow, and that there may have been substantial quantitiesof liquid water on the surface, but after a period of 600million to several billion years,[43] a runaway greenhouseeect was caused by the evaporation of that original wa-ter, which generated a critical level of greenhouse gasesin its atmosphere.[44] Although the surface conditions onthe planet are no longer hospitable to any Earthlike lifethat may have formed before this event, it is possiblethat life exists in the lower and middle cloud layers ofVenus.[45][46][47]

Thermal inertia and the transfer of heat by winds in thelower atmosphere mean that the temperature of the Venu-sian surface does not vary signicantly between the nightand day sides, despite the planets extremely slow rota-tion. Winds at the surface are slow, moving at a few kilo-metres per hour, but because of the high density of theatmosphere at the Venusian surface, they exert a signi-cant amount of force against obstructions, and transportdust and small stones across the surface. This alone wouldmake it dicult for a human to walk through, even if theheat, pressure and lack of oxygen were not a problem.[48]

Above the dense CO2 layer are thick clouds consistingmainly of sulfur dioxide and sulfuric acid droplets.[49][50]These clouds reect and scatter about 90% of the sunlightthat falls on them back into space, and prevent visual ob-servation of the Venusian surface. The permanent cloudcover means that although Venus is closer than Earth tothe Sun, the Venusian surface is not as well lit. Strong 85m/s (300 km/h) winds at the cloud tops circle the planetabout every four to ve Earth days.[51] Venusian windsmove at up to 60 times the speed of the planets rotation,whereas Earths fastest winds are only 1020% rotationspeed.[52]

The surface of Venus is eectively isothermal; it re-tains a constant temperature not only between day andnight but between the equator and the poles.[1][53] Theplanets minute axial tiltless than 3, compared to23 on Earthalso minimizes seasonal temperaturevariation.[54] The only appreciable variation in tempera-

ture occurs with altitude. The highest point on Venus,Maxwell Montes, is therefore the coolest point on theplanet, with a temperature of about 655 K (380 C) andan atmospheric pressure of about 4.5MPa (45 bar).[55][56]In 1995, the Magellan probe imaged a highly reectivesubstance at the tops of the highest mountain peaks thatbore a strong resemblance to terrestrial snow. This sub-stance arguably formed from a similar process to snow,albeit at a far higher temperature. Too volatile to con-dense on the surface, it rose in gas form to cooler higherelevations, where it then fell as precipitation. The identityof this substance is not known with certainty, but specu-lation has ranged from elemental tellurium to lead sulde(galena).[57]

The clouds of Venus are capable of producing lightningmuch like the clouds on Earth.[58] The existence oflightning had been controversial since the rst sus-pected bursts were detected by the Soviet Veneraprobes. In 20062007 Venus Express clearly detectedwhistler mode waves, the signatures of lightning. Theirintermittent appearance indicates a pattern associatedwith weather activity. The lightning rate is at least half ofthat on Earth.[58] In 2007 the Venus Express probe dis-covered that a huge double atmospheric vortex exists atthe south pole.[59][60]

Another discovery made by the Venus Express probe in2011 is that an ozone layer exists high in the atmosphereof Venus.[61]

On January 29, 2013, ESA scientists reported that theionosphere of the planet Venus streams outwards in amanner similar to the ion tail seen streaming from acomet under similar conditions.[62][63]

Atmospheric composition

Synthetic stick absorption spectrum of a simple gas mix-ture corresponding to Earths atmosphere

Venusian atmosphere composition based on HITRAN

5data[64] created using Hitran on the Web system.[65]Green colour water vapour, red carbon dioxide, WN wavenumber (other colours have dierent meanings,lower wavelengths on the right, higher on the left).

1.5 Magnetic eld and core

In 1967, Venera 4 found the Venusian magnetic eld tobe much weaker than that of Earth. This magnetic eldis induced by an interaction between the ionosphere andthe solar wind,[66][67] rather than by an internal dynamo inthe core like the one inside Earth. Venuss small inducedmagnetosphere provides negligible protection to the at-mosphere against cosmic radiation. This radiation mayresult in cloud-to-cloud lightning discharges.[68]

The lack of an intrinsic magnetic eld at Venus was sur-prising given it is similar to Earth in size, and was ex-pected also to contain a dynamo at its core. A dynamorequires three things: a conducting liquid, rotation, andconvection. The core is thought to be electrically con-ductive and, although its rotation is often thought to betoo slow, simulations show it is adequate to produce adynamo.[69][70] This implies the dynamo is missing be-cause of a lack of convection in the Venusian core. OnEarth, convection occurs in the liquid outer layer of thecore because the bottom of the liquid layer is much hotterthan the top. On Venus, a global resurfacing event mayhave shut down plate tectonics and led to a reduced heatux through the crust. This caused the mantle tempera-ture to increase, thereby reducing the heat ux out of thecore. As a result, no internal geodynamo is available todrive a magnetic eld. Instead, the heat energy from thecore is being used to reheat the crust.[71]

One possibility is that Venus has no solid inner core,[72] orthat its core is not cooling, so that the entire liquid part ofthe core is at approximately the same temperature. An-other possibility is that its core has already completely so-lidied. The state of the core is highly dependent on theconcentration of sulfur, which is unknown at present.[71]

The weak magnetosphere around Venus means that thesolar wind is interacting directly with its outer atmo-sphere. Here, ions of hydrogen and oxygen are beingcreated by the dissociation of neutral molecules from ul-traviolet radiation. The solar wind then supplies energythat gives some of these ions sucient velocity to es-cape Venuss gravity eld. This erosion process resultsin a steady loss of low-mass hydrogen, helium, and oxy-gen ions, whereas higher-mass molecules, such as carbondioxide, are more likely to be retained. Atmospheric ero-sion by the solar wind probably led to the loss of mostof Venuss water during the rst billion years after itformed. The erosion has increased the ratio of higher-mass deuterium to lower-mass hydrogen in the upper at-mosphere by 150 times compared to the ratio in the loweratmosphere.[73]

2 Orbit and rotation

Venus orbits the Sun at an average distance of about 108 millionkilometres (about 0.7 AU) and completes an orbit every 224.65days. Venus is the second planet from the Sun and orbits the Sunapproximately 1.6 times (yellow trail) in Earths 365 days (bluetrail)

Venus orbits the Sun at an average distance of about 0.72AU (108,000,000 km; 67,000,000 mi), and completesan orbit every 224.65 days. Although all planetary or-bits are elliptical, Venuss orbit is the closest to circular,with an eccentricity of less than 0.01.[1] When Venus liesbetween Earth and the Sun, a position known as inferiorconjunction, it makes the closest approach to Earth ofany planet at an average distance of 41 million km.[1]The planet reaches inferior conjunction every 584 days,on average.[1] Owing to the decreasing eccentricity ofEarths orbit, the minimum distances will become greaterover tens of thousands of years. From the year 1 to 5383,there are 526 approaches less than 40 million km; thenthere are none for about 60,158 years.[74]

All the planets of the Solar System orbit the Sun in ananti-clockwise direction as viewed from above Earthsnorth pole. Most planets also rotate on their axes inan anti-clockwise direction, but Venus rotates clock-wise (called "retrograde" rotation) once every 243 Earthdaysthe slowest rotation period of any planet. Becauseits rotation is so slow, it is highly spherical.[75] A Venu-sian sidereal day thus lasts longer than a Venusian year(243 versus 224.7 Earth days). Venuss equator rotatesat 6.5 km/h (4.0 mph), whereas Earths is approximately1,670 km/h (1,040 mph).[76] Venuss rotation has sloweddown by 6.5 min per Venusian sidereal day in the 16years between the Magellan spacecraft and Venus Ex-press visits.[77] Because of the retrograde rotation, thelength of a solar day on Venus is signicantly shorter thanthe sidereal day, at 116.75 Earth days (making the Venu-sian solar day shorter than Mercury's 176 Earth days);

6 3 OBSERVATION

one Venusian year is about 1.92 Venusian (solar) dayslong.[78] To an observer on the surface of Venus, the Sunwould rise in the west and set in the east, though the Suncannot be seen from the surface due to Venuss opaqueclouds.[78]

Venus may have formed from the solar nebula with a dif-ferent rotation period and obliquity, reaching its currentstate because of chaotic spin changes caused by planetaryperturbations and tidal eects on its dense atmosphere, achange that would have occurred over the course of bil-lions of years. The rotation period of Venus may rep-resent an equilibrium state between tidal locking to theSuns gravitation, which tends to slow rotation, and anatmospheric tide created by solar heating of the thickVenusian atmosphere.[79][80] The 584-day average inter-val between successive close approaches to Earth is al-most exactly equal to 5 Venusian solar days,[81] but thehypothesis of a spinorbit resonance with Earth has beendiscounted.[82]

Venus has no natural satellites,[83] though the asteroid2002 VE68 presently maintains a quasi-orbital relation-ship with it.[84][85] Besides this quasi-satellite, it hastwo other temporary co-orbitals, 2001 CK32 and 2012XE133.[86] In the 17th century, Giovanni Cassini re-ported a moon orbiting Venus, which was named Neithand numerous sightings were reported over the following200 years, but most were determined to be stars in thevicinity. Alex Alemis and David Stevenson's 2006 studyof models of the early Solar System at the California In-stitute of Technology shows Venus likely had at least onemoon created by a huge impact event billions of yearsago.[87] About 10 million years later, according to thestudy, another impact reversed the planets spin directionand caused the Venusian moon gradually to spiral inwarduntil it collided and merged with Venus.[88] If later im-pacts created moons, these were absorbed in the sameway. An alternative explanation for the lack of satellitesis the eect of strong solar tides, which can destabilizelarge satellites orbiting the inner terrestrial planets.[83]

3 Observation

Venus is always brighter than any star (apart from theSun). The greatest luminosity, apparent magnitude4.9,[8] occurs during crescent phase when it is nearEarth. Venus fades to about magnitude 3 when it isbacklit by the Sun.[7] The planet is bright enough to beseen in a mid-day clear sky,[89] and it can be easy to seewhen the Sun is low on the horizon. As an inferior planet,it always lies within about 47 of the Sun.[9]

Venus overtakes Earth every 584 days as it orbits theSun.[1] As it does so, it changes from the Evening Star,visible after sunset, to the Morning Star, visible be-fore sunrise. AlthoughMercury, the other inferior planet,reaches a maximum elongation of only 28 and is of-

Venus is always brighter than the brightest stars outside the SolarSystem, as can be seen here over the Pacic Ocean

Phases of Venus and evolution of its apparent diameter

ten dicult to discern in twilight, Venus is hard to misswhen it is at its brightest. Its greater maximum elonga-tion means it is visible in dark skies long after sunset.As the brightest point-like object in the sky, Venus is acommonly misreported "unidentied ying object". U.S.President Jimmy Carter reported having seen a UFO in1969, which later analysis suggested was probably Venus.Countless other people have mistaken Venus for some-thing more exotic.[90]

As it moves around its orbit, Venus displays phases likethose of the Moon in a telescopic view. The planetpresents a small full image when it is on the oppositeside of the Sun. It shows a larger quarter phase whenit is at its maximum elongations from the Sun, and is atits brightest in the night sky, and presents a much largerthin crescent in telescopic views as it comes around tothe near side between Earth and the Sun. Venus is at itslargest and presents its new phase when it is betweenEarth and the Sun. Its atmosphere can be seen in a tele-scope by the halo of light refracted around it.[9]

73.1 Transits

2004 transit of Venus

Main articles: Transits of Venus and Transit of Venus,2012

The Venusian orbit is slightly inclined relative to Earthsorbit; thus, when the planet passes between Earth and theSun, it usually does not cross the face of the Sun. Transitsof Venus occur when the planets inferior conjunction co-incides with its presence in the plane of Earths orbit.Transits of Venus occur in cycles of 243 years with thecurrent pattern of transits being pairs of transits separatedby eight years, at intervals of about 105.5 years or 121.5yearsa pattern rst discovered in 1639 by the Englishastronomer Jeremiah Horrocks.[91]

The latest pair was June 8, 2004 and June 56, 2012.The transit could be watched live from many online out-lets or observed locally with the right equipment andconditions.[92]

The preceding pair of transits occurred in December1874 and December 1882; the following pair will occurin December 2117 and December 2125.[93] Historically,transits of Venus were important, because they allowedastronomers to determine the size of the astronomicalunit, and hence the size of the Solar System as shown byHorrocks in 1639.[94] Captain Cook's exploration of theeast coast of Australia came after he had sailed to Tahitiin 1768 to observe a transit of Venus.[95][96]

3.2 Ashen lightA long-standing mystery of Venus observations is the so-called ashen lightan apparent weak illumination of itsdark side, seen when the planet is in the crescent phase.The rst claimed observation of ashen light was made in

1643, but the existence of the illumination has never beenreliably conrmed. Observers have speculated it may re-sult from electrical activity in the Venusian atmosphere,but it could be illusory, resulting from the physiologicaleect of observing a bright, crescent-shaped object.[97]

4 Studies

4.1 Early studies

The "black drop eect" as recorded during the 1769 transit

Venus was known to ancient civilizations both as themorning star and as the evening star, names that re-ect the early assumption that these were two separateobjects. The Venus tablet of Ammisaduqa, dated 1581BCE, shows the Babylonians understood the two were asingle object, referred to in the tablet as the bright queenof the sky, and could support this view with detailedobservations.[98] The Greeks thought of the two as sep-arate stars, Phosphorus and Hesperus, until the time ofPythagoras in the sixth century BC.[99] The Romans des-ignated the morning aspect of Venus as Lucifer, literallyLight-Bringer, and the evening aspect as Vesper, bothliteral translations of the respective Greek names.The transit of Venus was rst observed in 1032 by thePersian astronomer Avicenna, who concluded Venus iscloser to Earth than the Sun,[100] and established Venuswas, at least sometimes, below the Sun.[101] In the 12thcentury, the Andalusian astronomer Ibn Bajjah observedtwo planets as black spots on the face of the Sun, whichwere later identied as the transits of Venus and Mercuryby the Maragha astronomer Qotb al-Din Shirazi in the

8 5 EXPLORATION

13th century.[102] The transit of Venus was also observedby Jeremiah Horrocks on 4 December 1639 (24 Novem-ber under the Julian calendar in use at that time), alongwith his friend, William Crabtree, at each of their respec-tive homes.[103]

EARTH

Galileo's discovery that Venus showed phases (although remain-ing near the Sun in Earths sky) proved that it orbits the Sun andnot Earth

When the Italian physicist Galileo Galilei rst observedthe planet in the early 17th century, he found it showedphases like the Moon, varying from crescent to gibbousto full and vice versa. When Venus is furthest from theSun in the sky, it shows a half-lit phase, and when it isclosest to the Sun in the sky, it shows as a crescent or fullphase. This could be possible only if Venus orbited theSun, and this was among the rst observations to clearlycontradict the Ptolemaic geocentric model that the SolarSystem was concentric and centered on Earth.[104][105]

The atmosphere of Venus was discovered in 1761 by Rus-sian polymath Mikhail Lomonosov.[106][107] Venuss at-mosphere was observed in 1790 by German astronomerJohann Schrter. Schrter found when the planet was athin crescent, the cusps extended throughmore than 180.He correctly surmised this was due to scattering of sun-light in a dense atmosphere. Later, American astronomerChester Smith Lyman observed a complete ring aroundthe dark side of the planet when it was at inferior conjunc-tion, providing further evidence for an atmosphere.[108]The atmosphere complicated eorts to determine a rota-tion period for the planet, and observers such as Italian-born astronomer Giovanni Cassini and Schrter incor-rectly estimated periods of about 24 h from the motionsof markings on the planets apparent surface.[109]

4.2 Ground-based researchLittle more was discovered about Venus until the 20thcentury. Its almost featureless disc gave no hint what itssurface might be like, and it was only with the develop-ment of spectroscopic, radar and ultraviolet observationsthat more of its secrets were revealed. The rst UV obser-vations were carried out in the 1920s, when Frank E. Ross

Modern telescopic view of Venus from Earths surface

found that UV photographs revealed considerable detailthat was absent in visible and infrared radiation. He sug-gested this was due to a dense, yellow lower atmospherewith high cirrus clouds above it.[110]

Spectroscopic observations in the 1900s gave the rstclues about the Venusian rotation. Vesto Slipher tried tomeasure the Doppler shift of light from Venus, but foundhe could not detect any rotation. He surmised the planetmust have a much longer rotation period than had previ-ously been thought.[111] Later work in the 1950s showedthe rotation was retrograde. Radar observations of Venuswere rst carried out in the 1960s, and provided the rstmeasurements of the rotation period, which were close tothe modern value.[112]

Radar observations in the 1970s revealed details of theVenusian surface for the rst time. Pulses of radio waveswere beamed at the planet using the 300 m (980 ft) ra-dio telescope at Arecibo Observatory, and the echoes re-vealed two highly reective regions, designated the Alphaand Beta regions. The observations also revealed a brightregion attributed tomountains, which was calledMaxwellMontes.[113] These three features are now the only oneson Venus that do not have female names.[114]

5 ExplorationMain article: Observations and explorations of Venus

5.1 Early eorts

The rst robotic space probe mission to Venus, and therst to any planet, began on 12 February 1961, with thelaunch of the Venera 1 probe. The rst craft of the oth-erwise highly successful Soviet Venera program, Venera1 was launched on a direct impact trajectory, but contact

5.3 Surface and atmospheric science 9

Mariner 2, launched in 1962

was lost seven days into the mission, when the probe wasabout 2 million km from Earth. It was estimated to havepassed within 100,000 km of Venus in mid-May.[115]

The United States exploration of Venus also started badlywith the loss of the Mariner 1 probe on launch. The sub-sequent Mariner 2 mission, after a 109-day transfer orbiton 14 December 1962, became the worlds rst success-ful interplanetary mission, passing 34,833 km above thesurface of Venus. Its microwave and infrared radiometersrevealed that although the Venusian cloud tops were cool,the surface was extremely hotat least 425 C, conrm-ing previous Earth-based measurements[116] and nallyending any hopes that the planet might harbour ground-based life. Mariner 2 also obtained improved estimatesof its mass and of the astronomical unit, but was unableto detect either a magnetic eld or radiation belts.[117]

5.2 Atmospheric entry

The Soviet Venera 3 probe crash-landed on Venus on 1March 1966. It was the rst man-made object to enter theatmosphere and strike the surface of another planet. Itscommunication system failed before it was able to returnany planetary data.[118] On 18 October 1967, Venera 4successfully entered the atmosphere and deployed scienceexperiments. Venera 4 showed the surface temperaturewas even hotter than Mariner 2 had measured, at almost500 C, and the atmosphere was 90 to 95% carbon diox-ide. The Venusian atmosphere was considerably denserthan Venera 4s designers had anticipated, and its slowerthan intended parachute descent meant its batteries randown before the probe reached the surface. After return-ing descent data for 93 minutes, Venera 4s last pressurereading was 18 bar at an altitude of 24.96 km.[118]

One day later on 19 October 1967, Mariner 5 conducteda y-by at a distance of less than 4000 km above the cloudtops. Mariner 5 was originally built as a backup for theMars-boundMariner 4; when thatmissionwas successful,the probe was retted for a Venus mission. A suite of

Pioneer Venus Multiprobe

instruments more sensitive than those on Mariner 2, inparticular its radio occultation experiment, returned dataon the composition, pressure and density of the Venusianatmosphere.[119] The joint Venera 4 Mariner 5 data wasanalysed by a combined Soviet-American science teamin a series of colloquia over the following year,[120] in anearly example of space cooperation.[121]

Armed with the lessons and data learned from Venera 4,the Soviet Union launched the twin probes Venera 5 andVenera 6 ve days apart in January 1969; they encoun-tered Venus a day apart on 16 and 17 May. The probeswere strengthened to improve their crush depth to 25 barand were equipped with smaller parachutes to achieve afaster descent. Because then-current atmospheric modelsof Venus suggested a surface pressure of between 75 and100 bar, neither was expected to survive to the surface.After returning atmospheric data for a little over 50 min-utes, they were both crushed at altitudes of approximately20 km before going on to strike the surface on the nightside of Venus.[118]

5.3 Surface and atmospheric science

Venera 7 represented an eort to return data from theplanets surface, and was constructed with a reinforceddescent module capable of withstanding a pressure of180 bar. The module was precooled before entry andequipped with a specially reefed parachute for a rapid 35-minute descent. While entering the atmosphere on 15December 1970, the parachute is believed to have par-tially torn, and the probe struck the surface with a hard,

10 5 EXPLORATION

yet not fatal, impact. Probably tilted onto its side, it re-turned a weak signal, supplying temperature data for 23minutes, the rst telemetry received from the surface ofanother planet.[118]

180-degree panorama of the Venusian surface from the SovietVenera 9 lander

The Venera program continued with Venera 8 sendingdata from the surface for 50 minutes, after entering theatmosphere on 22 July 1972. Venera 9, which entered theatmosphere of Venus on 22 October 1975, and Venera10, which entered the atmosphere three days later, sentthe rst images of the Venusian landscape. The two land-ing sites presented dierent terrains in the immediatevicinities of the landers: Venera 9 had landed on a 20-degree slope scattered with boulders around 3040 cmacross; Venera 10 showed basalt-like rock slabs inter-spersed with weathered material.[122]

The Pioneer Venus orbiter

In the meantime, the United States had sent the Mariner10 probe on a gravitational slingshot trajectory past Venuson its way to Mercury. On 5 February 1974, Mariner10 passed within 5790 km of Venus, returning over4000 photographs as it did so. The images, the bestthen achieved, showed the planet to be almost feature-less in visible light, but ultraviolet light revealed detailsin the clouds that had never been seen in Earth-boundobservations.[123]

The American Pioneer Venus project consisted of twoseparate missions.[124] The Pioneer Venus Orbiter was in-serted into an elliptical orbit around Venus on 4 Decem-ber 1978, and remained there for over 13 years, study-ing the atmosphere and mapping the surface with radar.The Pioneer Venus Multiprobe released a total of fourprobes, which entered the atmosphere on 9 December1978, returning data on its composition, winds and heat

uxes.[125]

Position of Venera landing sites returning images form the sur-face

Four more Venera lander missions took place over thenext four years, with Venera 11 and Venera 12 detect-ing Venusian electrical storms;[126] and Venera 13 andVenera 14, landing on 1 and 5 March 1982, returningthe rst colour photographs of the surface. All four mis-sions deployed parachutes for braking in the upper at-mosphere, then released them at altitudes of 50 km, thedense lower atmosphere providing enough friction to al-low for unaided soft landings. Both Venera 13 and 14analysed soil samples with an on-board X-ray uores-cence spectrometer, and attempted to measure the com-pressibility of the soil with an impact probe.[126] Venera14 struck its own ejected camera lens cap and its probefailed to contact the soil.[126] The Venera program cameto a close in October 1983, when Venera 15 and Venera16 were placed in orbit to conduct mapping of the Venu-sian terrain with synthetic aperture radar.[127]

In 1985, the Soviet Union took advantage of the oppor-tunity to combine missions to Venus and Comet Halley,which passed through the inner Solar System that year.En route to Halley, on 11 and 15 June 1985, the twospacecraft of the Vega program each dropped a Venera-style probe (of which Vega 1s partially failed) and re-leased a balloon-supported aerobot into the upper atmo-sphere. The balloons achieved an equilibrium altitude ofaround 53 km, where pressure and temperature are com-parable to those at Earths surface. They remained op-erational for around 46 hours, and discovered the Venu-sian atmosphere was more turbulent than previously be-lieved, and subject to high winds and powerful convectioncells.[128][129]

5.4 Radar mappingEarly Earth-based radar provided a basic idea of the sur-face. The Pioneer Venus and the Veneras provided im-proved resolution.The United States Magellan probe was launched on 4May 1989, with a mission to map the surface of Venus

5.5 Current and future missions 11

Magellan radar topographical map of Venus (false colour)

Five global views of Venus byMagellan.

with radar.[26] The high-resolution images it obtainedduring its 4 years of operation far surpassed all priormaps and were comparable to visible-light photographsof other planets. Magellan imaged over 98% of the Venu-sian surface by radar,[130] and mapped 95% of its gravityeld. In 1994, at the end of its mission, Magellan was sentto its destruction into the atmosphere of Venus to quan-tify its density.[131] Venus was observed by the Galileoand Cassini spacecraft during y-bys on their respectivemissions to the outer planets, but Magellan was the lastdedicated mission to Venus for over a decade.[132][133]

5.5 Current and future missionsNASAs MESSENGER mission to Mercury performedtwo y-bys of Venus in October 2006 and June 2007, to

slow its trajectory for an eventual orbital insertion ofMer-cury in March 2011. It collected scientic data on Venusduring both y-bys.[134]

The Venus Express probe was designed and built by theEuropean Space Agency. Launched on 9 November2005 by a Russian Soyuz-Fregat rocket procured throughStarsem, it successfully assumed a polar orbit aroundVenus on 11 April 2006.[135] The probe is undertaking adetailed study of the Venusian atmosphere and clouds, in-cluding mapping of the planets plasma environment andsurface characteristics, particularly temperatures. One ofthe rst results from Venus Express is the discovery thata huge double atmospheric vortex exists at the southernpole.[135]

Artists impression of a Stirling cooled Venus Rover.[136]

The Japan Aerospace Exploration Agency (JAXA) de-vised a Venus orbiter, Akatsuki (formerly Planet-C),which was launched on 20 May 2010, but the craft failedto enter orbit in December 2010. Hopes remain that theprobe can successfully hibernate and make another in-sertion attempt in six years. Planned investigations in-cluded surface imaging with an infrared camera and ex-periments designed to conrm the presence of lightning,as well as the determination of the existence of currentsurface volcanism.[137]

The European Space Agency (ESA) hopes to launch amission to Mercury in 2016, called BepiColombo, whichwill perform two y-bys of Venus before it reaches Mer-cury orbit in 2020.[138][139]

NASA will launch the Solar Probe Plus in 2018, whichwill perform seven Venus y-bys during its six-year, 24-orbit reconnaissance of the Sun.[140]

Under its New Frontiers Program, NASA has proposed alander mission called the Venus In-Situ Explorer to landon Venus to study surface conditions and investigate theelemental and mineralogical features of the regolith. Theprobe would be equipped with a core sampler to drill intothe surface and study pristine rock samples not weath-ered by the harsh surface conditions. A Venus atmo-spheric and surface probe mission, Surface and Atmo-sphere Geochemical Explorer (SAGE), was selected byNASA as a candidate mission study in the 2009 New

12 7 COLONIZATION AND TERRAFORMING

Frontiers selection,[141] but the mission was not selectedfor ight.

Venus aircraft concept

The Venera-D (Russian: -) probe is a proposedRussian space probe to Venus, to be launched around2016, to make remote-sensing observations around theplanet and deploying a lander, based on the Venera de-sign, capable of surviving for a long duration on the sur-face. Other proposed Venus exploration concepts includerovers, balloons, and aeroplanes.[142]

In late 2013 the Venus Spectral Rocket Experiment tookplace, which launched a sub-orbital space telescope.

5.6 Manned y-by conceptMain article: Manned Venus Flyby

A manned Venus y-by mission, using Apollo programhardware, was proposed in the late 1960s.[143] The mis-sion was planned to launch in late October or earlyNovember 1973, and would have used a Saturn V to sendthree men to y past Venus in a ight lasting approxi-mately one year. The spacecraft would have passed ap-proximately 5,000 km (3,100 mi) from the surface ofVenus about four months later.[143] Inspiration Mars in-cludes a manned Venus yby in their 2021 mission.[144]

5.7 Sample returnVarious concepts for a Venus sample return include ahigh-speed upper atmosphere collection, an atmospheresample return by slowing down and entering then return-ing, and a surface sample return.[145]

5.8 Spacecraft timelineThis is a list of attempted and successful spacecraft thathave left Earth to explore Venus more closely.[146] Venushas also been imaged by the Hubble Space Telescope in

Earth orbit, and distant telescopic observations are an-other source of information about Venus.

Venera-D is a possible Russian mission in the 2020s[148]

6 In cultureSee also Venus (mythology), Venus (astrology) andHistorical observations and impactThroughout history and cultures, the planet has been ofremarkable importance as an especial object of observa-tion, reection and projection. Popular beliefs and obser-vations resulted in dierent and in parts similar patternsin mythology as well as phenomenological descriptions,attributions and depictions, e.g. in astrology. Such devel-opments in manifestations of human thought reect theplanets image as a result of early observations of Venusand their impact on culture and science.

6.1 EtymologyThe adjective Venusian is commonly used for items re-lated to Venus, though the Latin adjective is the rarelyused Venerean; the archaic Cytherean is still occasion-ally encountered. Venus is the only planet in the SolarSystem that is named after a female gure.[lower-alpha 1](Three dwarf planetsCeres, Eris and Haumeaalongwith many of the rst discovered asteroids[149] and somemoons (such as the Galilean moons) also have femininenames. Earth and the Moon also have feminine namesin many languagesGaia/Terra, Selene/Lunabut thefemale mythological gures who personied them werenamed after them, not the other way around.)[150]

6.2 Venus symbolMain article: Venus symbolThe astronomical symbol for Venus is the same asthat used in biology for the female sex: a circle with asmall cross beneath.[151] The Venus symbol also repre-sents femininity, and in Western alchemy stood for themetal copper.[151] Polished copper has been used for mir-rors from antiquity, and the symbol for Venus has some-times been understood to stand for the mirror of thegoddess.[151]

7 Colonization and terraformingMain articles: Colonization of Venus and Terraformingof VenusOwing to its extremely hostile conditions, a surface

13

Artists conception of a terraformed Venus

colony on Venus is not possible with current technol-ogy. The atmospheric pressure and temperature ap-proximately fty kilometres above the surface are sim-ilar to those at Earths surface and Earth air (nitro-gen and oxygen) would be a lifting gas in the Venu-sian atmosphere of mostly carbon dioxide. This hasled to proposals for oating cities in the Venu-sian atmosphere.[152] Aerostats (lighter-than-air balloons)could be used for initial exploration and ultimately forpermanent settlements.[152] Among the many engineer-ing challenges are the dangerous amounts of sulfuric acidat these heights.[152]

8 See also Aspects of Venus Mariner 10 Space probe to Venus 2001 CK32 2002 VE68 2012 XE133 Geodynamics of Venus Geology of Venus Observations and explorations of Venus Venus zone

9 Notes[1] Goddesses such asGaia and Terra were named after Earth,

and not vice versa.

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[127] Greeley, Ronald; Batson, Raymond M. (2007). PlanetaryMapping. Cambridge University Press. p. 47. ISBN 978-0-521-03373-2. Retrieved 2009-07-19.

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[132] Van Pelt, Michel (2006). Space invaders: how roboticspacecraft explore the Solar System. Springer. pp. 186189. ISBN 0-387-33232-4.

[133] Davis, Andrew M.; Holland, Heinrich D.; Turekian, KarlK. (2005). Meteorites, comets, and planets. Elsevier. p.489. ISBN 0-08-044720-1.

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[144] NBC

[145] VENUS SAMPLE RETURN MISSIONS - A RANGEOF SCIENCE, A RANGE OF COSTS

[146] Chronology of Venus Exploration (NASA)

[147] The Planetary Society - An unheralded anniversary

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[149] Nicholson, Seth B. (1961). The Trojan Asteroids.Astronomical Society of the Pacic Leaets 8: 239.Bibcode:1961ASPL....8..239N.

[150] Cessna, Abby. Mythology of the Planets. Universe To-day. Fraser Cain. Retrieved 19 September 2011.

[151] Stearn, William (May 1968). The Origin of the Maleand Female Symbols of Biology. Taxon 11 (4): 109113. doi:10.2307/1217734. JSTOR 1217734.

[152] Landis, Georey A. (2003). Colonization of Venus.AIP Conference Proceedings 654 (1). pp. 11931198.doi:10.1063/1.1541418.

11 External links Venus Prole at NASAs Solar System Explorationsite

Missions to Venus (Hosted by NASA) Gallery of Venus exploration images (Hosted byNASA)

The Soviet Exploration of Venus, Image catalog Venus page at The Nine Planets NASA page about the Venera missions Magellan mission home page Pioneer Venus information from NASA Detailed information about transits of Venus Geody Venus, a search engine for surface features Maps of Venus in NASA World Wind Chasing Venus, Observing the Transits of VenusSmithsonian Institution Libraries

Venus Crater Database Lunar and Planetary Insti-tute

Calculate/show the current phase of Venus (U.S.Naval Observatory)

Venus AstronomyCast episode No. 50, includes fulltranscript.

Thorsten Dambeck: The Blazing Hell Behind theVeil, MaxPlanckResearch, 4/2009, p. 2633

Gray, Meghan (2009). Venus. Sixty Symbols.Brady Haran for the University of Nottingham.

Venus Exploration Themes February 2014

11.1 Cartographic resources 19

11.1 Cartographic resources PDS Map-a-Planet & Venus Nomenclature Gazeteer of Planetary Nomenclature Venus(USGS)

Map of Venus Movie of Venus at National Oceanic and Atmo-spheric Administration

20 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

12 Text and image sources, contributors, and licenses12.1 Text

Venus Source: http://en.wikipedia.org/wiki/Venus?oldid=655942758 Contributors: NathanBeach, Brion VIBBER, Eloquence, VickiRosenzweig, Mav, Bryan Derksen, Zundark, The Anome, Taw, Jeronimo, Malcolm Farmer, -- April, Mark, Ed Poor, Aidan Elliott-McCrea, Amillar, Alex.tan, Andre Engels, Eob, Danny, XJaM, JeLuF, William Avery, SimonP, GrahamN, Fonzy, Dwheeler, Olivier,Rickyrab, Fransvannes, Rbrwr, Spi, Seldon, Edward, Patrick, Infrogmation, Ken Arromdee, Michael Hardy, Tim Starling, Oliver Pereira,Lexor, Nixdorf, Ixfd64, Tango, Cyde, Minesweeper, Alo, Kosebamse, Shimmin, Egil, Looxix, Ihcoyc, Mdebets, Ahoerstemeier, Snoyes,CatherineMunro, TUF-KAT, TUF-KAT, Angela, Mark Foskey, Glenn, Poor Yorick, Kwekubo, Evercat, Lancevortex, Mxn, Raven in Orbit,Schneelocke, Hike395, Hashar, Timwi, RickK, Stone, Andrewman327, Doradus, Haukurth, CBDunkerson, Robertb-dc, Tpbradbury, Drag-ons ight, Furrykef, Taxman, Ringomassa, Head, Samsara, Traroth, Anupamsr, Bloodshedder, Raul654, Wetman, BenRG, Jeq, Owen,Lumos3, Phil Boswell, Robbot, MrJones, Celsius1414, Naddy, Modulatum, Smallweed, Chris Roy, Merovingian, Academic Challenger,Rursus, Geogre, Bkell, Hadal, UtherSRG, Wereon, Anthony, Peter L, Carnildo, ShutterBugTrekker, Nephelin, Centrx, Giftlite, Reuben-barton, Christopher Parham, Djinn112, Awolf002, Jyril, Sj, TOttenville8, Harp, Nichalp, Wolfkeeper, Tom harrison, Lupin, Herbee, Karn,Alterego, Everyking, Curps, Michael Devore, Henry Flower, Wikibob, Jackbrown, Joe Kress, Erdal Ronahi, Sdsher, GarethWyn, Kainaw,Rchandra, Gzornenplatz, Matt Crypto, Python eggs, Jackol, Bobblewik, Cam, Wmahan, Innitysnake, OldakQuill, ChicXulub, Gadum,Andycjp, DocSigma, Alexf, Geni, Xmnemonic, Chris Edgemon, Yath, Antandrus, The Singing Badger, HorsePunchKid, Zaha, MistToys,Piotrus, Vanished user 1234567890, Kusunose, FelineAvenger, Rdsmith4, Samy Merchi, RetiredUser2, Tomruen, Icairns, B.d.mills, Neu-trality, Urhixidur, Edsanville, Irpen, Ukexpat, Fg2, JohnArmagh, Deglr6328, Chmod007, M1ss1ontomars2k4, Marnevell, Lacrimosus,Spiy sperry, DanielCD, Ultratomio, EugeneZelenko, Indosauros, Mark Zinthefer, Discospinster, Rich Farmbrough, Avriette, Guanabot,BlueMars, Supercoop, FraKctured, Martin TB, Vsmith, Florian Blaschke, ArnoldReinhold, Rasmusdf, Ponder, D-Notice, Dbachmann,Mani1, Chrislee, MuDavid, Pavel Vozenilek, SpaceFrog, Bender235, NeilTarrant, Violetriga, Evice, Brian0918, RJHall, Ylee, Sfahey, ElC, Fenevad, Huntster, Joanjoc, Kwamikagami, Evand, Worldtraveller, Tverbeek, Remember, Art LaPella, Femto, Adambro, Bobo192,Circeus, Smalljim, NightDragon, .:Ajvol:., ZayZayEM, Elipongo, Angie Y., Nesnad, Kappa, La goutte de pluie, Jojit fb, Timsheridan,BillCook, Sam Korn, Fwb22, Gsklee, A2Kar, Jumbuck, Danski14, Bob rulz, Alansohn, Gary, Tablizer, Eric Kvaalen, Keenan Pepper,Moanzhu, Andrewpmk, Paleorthid, Andrew Gray, Sp82, Cbotman, AzaToth, Lectonar, Corwin8, JanSderback, Mlm42, Hu, Avenue,DreamGuy, Snowolf, Mbloore, Velella, BanyanTree, Juan Toledo, Rebroad, Evil Monkey, RainbowOfLight, Inge-Lyubov, Cmapm, Zx-cvbnm, Gene Nygaard, Dan East, HenryLi, Tr00st, Leopard, Red dwarf, Adrian.benko, BerserkerBen, Duke33, Feezo, Siafu, Gmaxwell,WilliamKF, Angr, Rorschach, Mel Etitis, Woohookitty, Jannex, DonPMitchell, ChrisNoe, TigerShark, Ylem, MrNexx, Volcanopele, De-crease789, Plek, BillC, Bigfrozenhead, Chris Mason, Zealander, Bricktop, Nefertum17, MONGO, Eleassar777, Pi@k, Tabletop, Keta,Kelisi, Ch'marr, TotoBaggins, BartBenjamin, Cat11, Steinbach, X444, Sengkang, GregorB, CharlesC, Jon Harald Sby, Mayz, Oldel-paso, Prashanthns, Smartech, Teemu Leisti, Driftwoodzebulin, Cataclysm, Emerson7, MrSomeone, Paxsimius, Mandarax, Ashmoo, Gra-ham87, Marskell, JiMidnite, Johnny Mnemonic, Deltabeignet, Magister Mathematicae, TAKASUGI Shinji, FreplySpang, RxS, Pentawing,Jcmo, Canderson7, Funkymuskrat, Drbogdan, Akubhai, Rjwilmsi, Urbane Legend, Vary, Hiberniantears, JoshuacUK, Tawker, Mentality,Heah, Mike Peel, Crazynas, Bubba73, Boccobrock, AndyKali, Brighterorange, Afterwriting, Ttwaring, Wkruse, GregAsche, Sango123,DirkvdM, Dbigwood, Yamamoto Ichiro, FayssalF, Titoxd, Ian Pitchford, SchuminWeb, RobertG, Crazycomputers, Finsen, Nivix, RexNL,Gurch, Arctic.gnome, Enon, R Lee E, TeaDrinker, Alphachimp, Malhonen, Srleer, DybrarH, Zotel, Gurubrahma, Glenn L, Kelpi,Phoenix2, King of Hearts, Chobot, Raincheerleader, Rewster, DVdm, PainMan, Mysekurity, Debivort, Cobaahema, Banaticus, Elfguy,Roboto de Ajvol, The Rambling Man, Satanael, Mercury McKinnon, TexasAndroid, Koveras, Deeptrivia, Jimp, RussBot, Kauner, Fabar-tus, Anonymous editor, Gspr, Witan, Qrasy, Hydrargyrum, Stephenb, Mithridates, Gaius Cornelius, CambridgeBayWeather, Cpuwhiz11,Kimchi.sg, Dorthonion, Bovineone, Wimt, Ebow, Anomalocaris, NawlinWiki, SEWilcoBot, Wiki alf, BGManofID, Itisan, Exir Kamal-abadi, RazorICE, Seegoon, Bmdavll, Irishguy, Brandon, Dppowell, Rmky87, Raven4x4x, Semperf, Tony1, Martinwilke1980, Wknight94,Noosfractal, Leptictidium, Manjithkaini, Bdell555, 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Scwlong, Salmar, Can't sleep, clown will eat me, VJDocherty, DHeyward, Murder1, Mrwuggs, As-trobhadauria, Wikipedia brown, Krsont, Andy120290, Addshore, Kcordina, Edivorce, Rocksandfossils, Aldaron, Krich, Robma, Nakon,TMW, Dreadstar, Wjtimmerman, Mini-Geek, Hgilbert, Jan.Kamenicek, Polonium, Omnipotence, Adrigon, SpiderJon, MonkeyMumford,Zonk43, Risker, Ck lostsword, FelisLeo, NeilFraser, Sarfa, Ohconfucius, GoldenTorc, Thejerm, SashatoBot, Mksword, NormalGoddess,Kuru, Titus III, John, JanderVK, Drahcir, Jrothwell, Soumyasch, Linnell, JoshuaZ, Kreuzfeld, JorisvS, Temple, Scetoaux, IronGargoyle,SpyMagician, Jess Mars, Keber, Heliogabulus, Chrisd87, Ckatz, The Man in Question, RandomCritic, A. Parrot, Serpentinite, Beetstra,Stevebritgimp, Jhpace1, George The Dragon, Xiaphias, Don Alessandro, Tobyw87, Kliqjaw, Ryulong, Sims2789, RichardF, Novangelis,Elb2000, Jose77, Peyre, Floridan, Politepunk, Papertiger, BranStark, Iridescent, Majorbonkers, Michaelbusch, Alessandro57, Scooter20,Newone, J Di, Igoldste, Takarada, CapitalR, Ewulp, Mssgill, Tawkerbot2, Dlohcierekim, George100, Poolkris, Arhain, P-Chan, CalebNo-ble, Sarvagnya, Vjamesv, Gustavh, JForget, Adam Keller, VoxLuna, CmdrObot, Ale jrb, Geremia, TheHerbalGerbil, Memetics, Sasho84,Tuvas, BeenAroundAWhile, N3X15, Runningonbrains, MiShogun, BKalesti, Ruslik0, GHe, Orannis, CuriousEric, Dwolsten, MarsRover,Todowd, Joelholdsworth, WeggeBot, Moreschi, Borislav Dopudja, Nilfanion, Ufviper, Rudjek, Schauf, Icek, Badseed, Nbound, Domini-canpapi82, ArgentTurquoise, Steel, DrunkenSmurf, Vanished user vjhsduheuiui4t5hjri, Gogo Dodo, Red Director, Zginder, MattButts,JFreeman, Flowerpotman, Llort, Ykliu, Scooteristi, Rafeal, SakuraKitsune45, Tdvance, Tawkerbot4, DumbBOT, Chrislk02, YorkBW, DocW, Paddles, Asenine, Robertinventor, Thenewestdoctorwho, Brad101, SteveMcCluskey, Sancort, Omicronpersei8, Cancun771, Theirish-pianist, Maat333, OakAve222, FrancoGG, Thijs!bot, Epbr123, Tepidpond, Interested2, Cassie, cole, Keraunos, Andyjsmith, Anthius,Halibut Thyme, Headbomb, Newton2, Ranger 1 (usurped), A3RO, HelenKMarks, Brichcja, Catsmoke, DoomsDay349, Grayshi, NickNumber, TangentCube, Dawnseeker2000, Natalie Erin, CTZMSC3, Northumbrian, Escarbot, KrakatoaKatie, AntiVandalBot, Yupik,MR 17, CommanderCool1654, Majorly, Yonatan, Luna Santin, Clarenceville Trojan, Ricnun, Opelio, MeNext, Dr. Submillimeter, Li-bLord, Farosdaughter, Jrizzy4, SkoreKeep, Aliwalla, Storkk, Myanw, PresN, Gkhan, JAnDbot, Deective, Husond, MER-C, Skomorokh,CosineKitty, Nthep, Something14, Janejellyroll, Miltopia, Db099221, Sln3412, LGDubs, Andonic, Natureguy1980, Roleplayer, Rentafer-ret, Argent Cerulean, Who is like God?, Hardee67, Rothorpe, Sami assahli, FaerieInGrey, Tomst, WolfmanSF, Murgh, Suradasa, Bongwar-

12.2 Images 21

rior, VoABot II, Sushant gupta, Bcsr4ever, Adam keller, Kuyabribri, Hasek is the best, JamesBWatson, Jerome Kohl, Eltener, , Thinkoutside the box, Stotan, Lucyin, Bigdan201, Avicennasis, Wikiwhat?, Catgut, Panser Born, Spookiejjr, Cyktsui, ArthurWeasley, Arbeiter,Torchiest, 28421u2232nfenfcenc, BilCat, Joeloveslego, Jc1346729, MorningGrace, IanUK, AdoreMila, Just James, Glen, DerHexer, JaGa,Megalodon99, TheRanger, Markco1, Kheider, Gjd001, Oren0, Bmf 51, Cli smith, Hdt83, MartinBot, Schmloof, FlieGerFaUstMe262,PAK Man, PatrickLMT, Vlink, Theodore141, Jim.henderson, Naohiro19, Rettetast, Jerry teps, Uriel8, R'n'B, CommonsDelinker, Alex-iusHoratius, Genesis12, Paranomia, Watch37264, J.delanoy, Pharaoh of the Wizards, Tinwelint, DrKiernan, Bogey97, DomBot, 16345,Uncle Dick, All Is One, Jameswheeleratskool, Mike.lifeguard, KrytenKoro, Anoushirvan, WarthogDemon, Thaurisil, Nemrac2, ABTU,Rod57, IdLoveOne, Vegasprof, Bot-Schafter, Katalaveno, McSly, Vandriel1325, Vineeth.vooppala, DJ1AM, Gurchzilla, Jancoop, (jar-barf), M-le-mot-dit, Mortbrew, WHeimbigner, NewEnglandYankee, Rominandreu, Fountains of Bryn Mawr, Gallador, Supersmell, SJP,Malerin, Salander86, Sopwith07, BigHairRef, Sunderland06, Myson45, Juliancolton, Haljackey, Cometstyles, Iamjasonyo, WJBscribe,Aaronbeemer, Burzmali, Gwen Gale, Zamonin, Natl1, LastChanceToBe, Belegur, Useight, Retal, Hork the Zombie, Gpetrov, Notori-ousG, Xiahou, Squids and Chips, Dialashop, Idioma-bot, BradDeharder, Spellcast, Domoregan, Glossologist, Wikieditor06, ACSE, Lights,Philfan108, Deor, VolkovBot, Thewolf37, ABF, Parishp, Mrh30, Hersfold, Joelikesweiner, Indubitably, Vlma111, Toddles29, Maile66,Katydidit, FergusM1970, WarddrBOT, Barneca, Sdsds, Philip Trueman, Tangz22, TXiKiBoT, DUBJAY04, BuickCenturyDriver, Dwmr,Inuendo, Z.E.R.O., Auent Rider, Gerrish, Finlux, Qxz, Someguy1221, Lradrama, DennyColt, Corvus cornix, MasterSci, Greatparty,JhsBot, Leafyplant, Sanfranman59, Lukezuke, Tranquility2007, Seb az86556, Pooblahsteak1234, Maxim, Quindraco, Damrung, Thep-erson427, Sultec, BigDunc, Pious7, Complex (de), Wearetheliving, Sarc37, Mcattell, Soulja nyn3, Pumpkin900, Sorrento11, Tzsche,Synthebot, Gorank4, Jimbob33, Enviroboy, Sai2020, Anna512, Burntsauce, FKmailliW, Gaaralover1991, Sampaultan, SchumiChamp,WatermelonPotion, Stephen J. 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12.2 Images File:Commons-logo.svg Source: http://upload.wikimedia.org/wikipedia/en/4/4a/Commons-logo.svg License: ? Contributors: ? Original

artist: ? File:Flag_of_Europe.svg Source: http://upload.wikimedia.org/wikipedia/commons/b/b7/Flag_of_Europe.svg License: Public domain

Contributors: File based on the specication given at [1]. Original artist: User:Verdy p, User:-x-, User:Paddu, User:Nightstallion, User:Funakoshi,

User:Jeltz, User:Dbenbenn, User:Zscout370

22 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

File:Flag_of_Japan.svg Source: http://upload.wikimedia.org/wikipedia/en/9/9e/Flag_of_Japan.svg License: PD Contributors: ? Originalartist: ?

File:Flag_of_the_Soviet_Union.svg Source: http://upload.wikimedia.org/wikipedia/commons/a/a9/Flag_of_the_Soviet_Union.svg Li-cense: Public domain Contributors: http://pravo.levonevsky.org/ Original artist:

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