# Venus

This is an image of Venus in true color. The surface is obscured by a thick blanket of clouds. Credit: NASA/Ricardo Nunes, http://www.astrosurf.com/nunes.

Some objects seem to wander around in the night sky relative to many of the visual points of light. At least one occasionally is present in the early morning before sunrise as the Morning Star and after sunset as the Evening Star, the planet Venus.

## Planetary astronomy

Venus orbits the Sun at an average distance of about 108 million kilometres (about 0.7 AU) and completes an orbit every 224.65 days. Credit: Lookang.
The phases of Venus and evolution of its apparent diameter. Credit: Statis Kalyvas.
This is a snapshot of the planetary orbital poles. Credit: Urhixidur.

"The spectrum of gaseous methane at 77 K in the 1.1-2.6 µm region [is] a benchmark for planetary astronomy".[1]

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."[2]

Venus is the second planet from the Sun and orbits it approximately 1.6 times (yellow trail) per Earth orbit (blue trail). Every 5 Earth years correspond to 8 Venus years.

"[A]xial tilt (also called obliquity) is the angle between an object's rotational axis, and a line perpendicular to its orbital plane. ... The planet Venus has an axial tilt of 177.3° because it is rotating in retrograde direction, opposite to other planets like Earth. ... The planet Uranus is rotating on its side in such a way that its rotational axis, and hence its north pole, is pointed almost in the direction of its orbit around the Sun. Hence the axial tilt of Uranus is 97°.[3]"[4]

"An orbital pole is either end of an imaginary line running through the center of an orbit perpendicular to the orbital plane, projected onto the celestial sphere. It is similar in concept to a celestial pole but based on the planet's orbit instead of the planet's rotation."[5]

"The north orbital pole of a celestial body is defined by the right-hand rule: If you curve the fingers of your right hand along the direction of orbital motion, with your thumb extended parallel to the orbital axis, the direction your thumb points is defined to be north."[5]

At right is a snapshot of the planetary orbital poles.[6] The field of view is about 30°. The yellow dot in the centre is the Sun's North pole. Off to the side, the orange dot is Jupiter's orbital pole. Clustered around it are the other planets: Mercury in pale blue (closer to the Sun than to Jupiter), "Venus in green, [the] Earth in blue, Mars in red, Saturn in violet, Uranus in grey [partly underneath Earth] and Neptune in lavender. Dwarf planet Pluto is the dotless cross off in Cepheus."[5]

Venus has a mean radius of 6,051.8 ± 1.0 km.[7]

## Theoretical Venus

This image shows a sequence of photographs by NASA's SDO spacecraft for Venus's path across the face of the Sun. Credit: NASA/SDO, AIA.

Def. the "second planet in our solar system,[8] named for the goddess; represented in astronomy and astrology by ♀"[9] is called Venus.

The image above shows a sequence of photographs by NASA's SDO spacecraft, taken in the extreme ultraviolet spectrun (171 Angstroms), and stitched together to show Venus's path across the face of the Sun. On June 5-6 2012, SDO collected images of one of the rarest predictable solar events: the transit of Venus across the face of the sun. This event happens in pairs eight years apart that are separated from each other by 105 or 121 years. The previous transit was in 2004 and the next will not happen until 2117.

## Astrognosy

Main sources: Astrognosy and Stellar astrognosy
This is a theoretical model for the interior of Venus. Credit: Urutseg.

On the right is a model for the interior structure of Venus.

## Electromagnetics

"In 1967, Venera-4 found the Venusian magnetic field is much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind,[10][11]"[12]

## Meteors

This is an image of Venus in the ultraviolet by the Magellan spacecraft. Credit: Magellan spacecraft, NASA.
This is a Magellan spacecraft image of Venus in the ultraviolet. Credit: Magellan and NASA.

In visual astronomy "[a]lmost no variation or detail can be seen in the clouds. ... The surface is obscured by a thick blanket of clouds. ... Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. ... [It has] thick clouds of sulfur dioxide ... [There are] lower and middle cloud layers ... [The] thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets.[13][14] These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of the Venusian surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well lit."[12]

"Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days.[15] Venusian winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed.[16]"[12]

"Average cloud-top wind speeds on Venus rose 33 percent between 2006 and 2012, jumping from 186 mph (300 km/h) to 249 mph (400 km/h), observations by Europe's Venus Express orbiter show."[17]

"This is an enormous increase in the already high wind speeds known in the atmosphere, ... Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred."[18]

The wind speeds are determined "by studying images captured by Venus Express between [50° N and S latitude, and tracking] the movements of tens of thousands of feature in the cloud tops some [70 km] above the planet's surface."[17]

"Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up 70 km/h over a time scale of 255 Earth days — slightly longer than a year on Venus".[19]

"Sometimes clouds took 3.9 days to zip all the way around Venus, for example, while on other occasions the journey required 5.3 days."[17]

"Although there is clear evidence that the average global wind speeds have increased, further investigations are needed in order to explain what drives the atmospheric circulation patterns that are responsible, and to explain the changes seen in localized areas on shorter timescales ... The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the solar system ... These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet."[20]

"Venus has a super-rotating atmosphere that whips around the planet once every four Earth days; Venus itself takes 243 Earth days to complete one rotation."[17]

## Gamma rays

"Concentrations of natural radioactive elements U, Th, and K in the Venusian mountain rocks were obtained by gamma ray spectrometers aboard the Vega 1 and Vega 2 descent modules that landed close to Mermaid Valley and the northeastern slope of Aphrodite Terra, respectively."[21]

"[T]he chemical composition of the Venusian rocks studied is similar to that of basic rocks of the earth's crust, tholeiitic basalts and gabbros."[21]

## X-rays

This Chandra X-ray Observatory image is the first X-ray image ever made of Venus. Credit: NASA/MPE/K.Dennerl et al..

The first ever X-ray image of Venus is shown at right. The "half crescent is due to the relative orientation of the Sun, Earth and Venus. The X-rays from Venus are produced by fluorescent radiation from oxygen and other atoms in the atmosphere between 120 and 140 kilometers above the surface of the planet. In contrast, the optical light from Venus is caused by the reflection from clouds 50 to 70 kilometers above the surface. Solar X-rays bombard the atmosphere of Venus, knock electrons out of the inner parts of atoms, and excite the atoms to a higher energy level. The atoms almost immediately return to their lower energy state with the emission of a fluorescent X-ray. A similar process involving ultraviolet light produces the visible light from fluorescent lamps."[22]

## Ultraviolets

An ultraviolet image of the planet Venus is taken on February 26, 1979, by the Pioneer Venus Orbiter. Credit: NASA.
Mariner 10 false color UV Venus image has been processed from Clear and Blue and UV filters. Credit: Ricardo Nunes.
Ultraviolet view of Venus is by the Hubble telescope, in false colour. Credit: NASA.

When imaged in the ultraviolet on the right, Venus appears like a gas dwarf object rather than a rocky object.

The image on the lower right has been re-processed through the clear, blue, and UV filters of Mariner 10 from the image taken of Venus by Mariner 10 on May 5, 1974, to show greater detail.

On the left is an image of Venus in the ultraviolet by the Hubble Space Telescope.

## Visuals

Venera 13 Lander image of the surface of Venus at 7.5 S, 303. E, east of Phoebe Regio. Credit: NASA, Soviet Space Program.

When imaged in visible light (right at page top) Venus appears like a gas dwarf rather than a rocky body. The same image result occurs when it is viewed in the ultraviolet.

On the right is a composite "Venera 13 Lander image of the surface of Venus at 7.5 S, 303. E, east of Phoebe Regio. Venera 13 survived on the surface for 2 hours, 7 minutes, long enough to obtain 14 images on 1 March, 1982. This color 170 degree panorama was produced using dark blue, green and red filters and has a resolution of 4 to 5 min. Part of the spacecraft is at the bottom of the image. Flat rock slabs and soil are visible. The true color is difficult to judge because the Venerian atmosphere filters out blue light. The surface composition is similar to terrestrial basalt. On the ground in foreground is a camera lens cover."[23]

## Violets

This image of Venus is taken through a violet filter by the Galileo spacecraft on February 14, 1990. Credit: NASA/JPL-Caltech.
This violet light image was taken in February 1990 by Galileo's Solid State Imaging System at range of about 2 million miles. Credit: NASA/JPL.

Violet photographs of the planet Venus taken in 1927 “recorded two nebulous bright streaks, or bands, running ... approximately at right angles to the terminator” that may be from the upper atmosphere.[24]

In 1959 "observations of the spectrum of the planet Venus, with spectrographs of low and high dispersion at the Georgetown College Observatory, show that a wide, continuous absorption band is present in the violet and near-ultraviolet."[25]

The image at the top right is from the Galileo spacecraft solid state imaging system taken on February 14, 1990. The satellite was about 2.7 million km from the planet. The highpass violet filter (418 nm) has been applied to emphasize the smaller scale cloud features. This rendition has been colorized bluish to emphasize subtle contrasts in the cloud markings. The sulfuric acid clouds indicate considerable convective activity. The filamentary dark features are composed of several dark nodules, like beads on a string, each about 96 km across.

The image at right is from a "series of pictures [that show] four views of the planet Venus obtained by Galileo's Solid State Imaging System at ranges of 1.4 to 2 million miles as the spacecraft receded from Venus. The pictures [the first two] were taken about 4 and 5 days after closest approach; those ... were taken about 6 days out, 2 hours apart [of which the image at right is the last]. In these violet-light images, north is at the top and the evening terminator to the left. The cloud features high in the planet's atmosphere rotate from right to left, from the limb through the noon meridian toward the terminator, traveling all the way around the planet once every four days. The motion can be seen by comparing the last two pictures, taken two hours apart. The other views show entirely different faces of Venus. These photographs are part of the 'Venus global circulation' sequence planned by the imaging team."[26]

## Greens

"Venus at times shows [the oxygen] green line emission with an intensity equal to terrestrial values [Slanger et al., 2001]. Furthermore, the intensity is quite variable, as is true for the much stronger O2( a-X) 1.27 μ emission."[27]

"In 1999, observations of the Venus nightglow with the Keck I telescope showed that the 5577 Å oxygen green line was a significant feature, comparable in intensity to the terrestrial green line. Subsequent measurements have been carried out at the Apache Point Observatory (APO) and again at Keck I, confirming the presence of the line with substantially varying intensity."[28]

"Ground-based studies suggest that the [557.7 nm oxygen green line] emission is correlated with the solar cycle."[29]

## Yellows

"Selected images of Venus [show] cloud configurations in yellow light".[30] These images are photographs taken between October 3, 1943, and March 14, 1945.[30]

## Reds

Venus is imaged at a wavelength of 630 nm (in the red). Credit: NASA.

Although shown in black and white, the image on the right was taken at 630 nm in the red.

"During the MESSENGER mission's second flyby of Venus, the Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) acquired images through all of its 11 narrow-band color filters of the approaching planet. The surface of Venus is shrouded in clouds, and the WAC images returned from the encounter show this cloud covered view, as seen in a previously released image. However, by processing the WAC images and "stretching" the gray scale used to display the images, subtle differences in the clouds of Venus are revealed, as seen in the image here. This WAC image was taken through a narrow-band filter centered at 630 nanometers, and in this stretched image, global circulation patterns can be seen in the atmosphere of Venus."[31]

## Infrareds

This is a false-color near-infrared image of lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990. Credit: NASA/JPL.

"The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)-X(v″) progression more than 3 decades ago."[32]

"Spectroscopic observations of the differential Doppler shift in a CO2 absorption line on Venus show that the upper atmospheric wind near the equator appears to have both a retrograde motion of about -85 ± 10 m s-1 ... and ... a periodically varying component, with an amplitude of about 40 ± 14 m s-1 and a period of 4.3 ± 0.2 days."[33]

At right is a false-color near-infrared image of the lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990.

"Bright slivers of sunlit high clouds are visible above and below the dark, glowing hemisphere. The spacecraft is about 100,000 kilometers (60,000 miles) above the planet. An infrared wavelength of 2.3 microns (about three times the longest wavelength visible to the human eye) was used. The map shows the turbulent, cloudy middle atmosphere some 50-55 kilometers (30- 33 miles) above the surface, 10-16 kilometers or 6-10 miles below the visible cloudtops. The red color represents the radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about -30 degrees Fahrenheit, at a pressure about 1/2 Earth's surface atmospheric pressure. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude."[34]

Using an imaging radar technique, the Magellan spacecraft was able to lift the veil from the face of Venus and produce this spectacular high resolution image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. Credit: Magellan Team, JPL, NASA.
This is a false color image of Venus produced from a global radar view of the surface by the Magellan probe while radar imaging between 1990-1994. Credit: NASA.

"The first un-ambiguous detection of Venus was made by [the] Jet Propulsion Laboratory (JPL) on 10 March 1961. A correct measurement of the AU soon followed."[35]

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."[2]

When viewed using radio astronomy, the resulting radar image, at left, shows that just beneath the cloud layers is a rocky planet.

## Lightning

"During the Soviet Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. The European Space Agency's Venus Express recorded abundant lightning in the high atmosphere.[36]"[12]

## Magnetospheres

"Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation. This radiation may result in cloud-to-cloud lightning discharges.[37]"[12]

"The weak magnetosphere around Venus means the solar wind is interacting directly with the outer atmosphere of the planet. Here, ions of hydrogen and oxygen are being created by the dissociation of neutral molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape the planet's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, while higher-mass molecules, such as carbon dioxide, are more likely to be retained."[12]

“Planets which generate magnetic fields in their interiors ... are surrounded by invisible magnetospheres. ... [I]n many respects, the magnetosphere of Venus is a scaled-down version of Earth’s. ... Earth’s magnetosphere is 10 times larger [than that of Venus]”[38]

## Coronal clouds

"A non-thermal, or “hot”, Venus corona of H atoms has been observed by Mariners 5 and 10 and Venera 9."[39]

"After more than two years in orbit still no Venus Express observations were published concerning the hot oxygen corona of Venus which could verify the corresponding controversial observations of Venera 11 and PVO, three decades ago."[40]

"Venus has a hot oxygen corona in addition to its hydrogen corona (Nagy et al., 1981) and charge-exchange between protons and oxygen is accidentally resonant."[41]

## Gaseous objects

Venus has been detected as a gaseous object using X-ray through infrared astronomy.

## Atmospheres

The image shows Venus Express data with an artist's impression of the tear-drop shaped ionosphere. Credit: ESA/Wei et al. (2012).
Pie chart of the atmosphere of Venus. Second pie chart is an expanded version of the trace elements that don't fit into the first one. Credit: Life of Riley.

"During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet. ... Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999. ... A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun. NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day."[42]

"The observations show that the night side ionosphere moved outward to at least 15 000 km from Venus' centre over a period of only a few hours," said Markus Fraenz, also from the Max Planck Institute for Solar System Research, who was the team leader and a co-author of the paper.[42] "It may possibly have extended for millions of kilometres, like an enormous tail."[42]

"Although we cannot determine the full length of the night-side ionosphere, since the orbit of Venus Express provides limited coverage, our results suggest that Venus' ionosphere resembled the teardrop-shaped ionosphere found around comets, rather than the more symmetrical, spherical shape which usually exists."[42]

"The side of Venus' ionosphere that faces away from the sun can billow outward like the tail of a comet, while the side facing the star remains tightly compacted, researchers said. ... "As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions," ESA officials said in a statement today (Jan. 29). It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down. Researchers observed the ionosphere stretch to at least 7,521 miles (12,104 kilometers) from the planet, said Yong Wei, a scientist at the Max Planck Institute in Katlenburg, Germany who worked on this research."[43]

"[B]ecause of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind.[44]"[12]

"The clouds of Venus are capable of producing lightning much like the clouds on Earth.[45] The existence of lightning had been controversial since the first suspected bursts were detected by the Soviet Venera probes. In 2006–07 Venus Express clearly detected whistler mode waves, the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. The lightning rate is at least half of that on Earth.[45] In 2007 the Venus Express probe discovered that a huge double atmospheric vortex exists at the south pole of the planet.[46][47]"[12]

"Another discovery made by the Venus Express probe in 2011 is that an ozone layer exists high in the atmosphere of Venus.[48]"[12]

"Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The atmospheric mass is 93 times that of Earth's atmosphere, while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. The density at the surface is 65 kg/m³ (6.5% that of water)."[12]

On the left are pie charts that show the approximate composition of Venus' atmosphere including some minor constituents.

## Meteorites

Main sources: Rocks/Meteorites and Meteorites

"While there is little or no water on Venus, there is a phenomenon which is quite similar to snow. The Magellan probe imaged a highly reflective substance at the tops of Venus's highest mountain peaks which bore a strong resemblance to terrestrial snow. This substance arguably formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gas form to cooler higher elevations, where it then fell as precipitation. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).[49]"[50]

## Craters

Impact craters are on the surface of Venus (image reconstructed from radar data) are shown. Credit: .
Image is from Magellan Venus Mission Radar mapping of the planet Venus, depicting the crater Mariko. Credit: NASA.
Addams crater is radar imaged on the surface of Venus. Credit: NASA's Magellan probe.

"The absence of evidence of lava flow accompanying any of the visible caldera remains an enigma. The planet has few impact craters".[12]

"After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne.[51][52]"[12]

"Almost a thousand impact craters on Venus are evenly distributed across its surface. ... On Venus, about 85% of the craters are in pristine condition. ... Venusian craters range from 3 km to 280 km in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere, they do not create an impact crater.[53] Incoming projectiles less than 50 meters in diameter will fragment and burn up in the atmosphere before reaching the ground.[54]"[12]

The second image down on the right is the crater Mariko.

Addams crater is in the third image down on the right.

"Magellan radar image [is] of Addams crater, Venus. The radar bright outflow associated with the 90 km crater stretches over 600 km to the east. (North is up.) The crater is located at 56.1S,98.9E in the Aino Planitia region."[55]

## Wanderers

Main sources: Astronomy/Wanderers and Wanderers
Venus is the Evening Star, next to a crescent moon. Credit: Shakil Mustafa.
Planet Venus rises above the horizon at dawn. Credit: DarrenBaker.
The "Venus transit" -- the apparent crossing of our planetary neighbor in front of the Sun -- was captured from the unique perspective of NASA's Sun-observing TRACE spacecraft. Credit: NASA/LMSAL.
The image of the Venus transit was taken with a home-made solar filter from baader solar film. Credit: Brocken Inaglory.
The photograph show a conjunction between Venus and Jupiter. Credit: Geraint Smith.
The planet Venus orbits just over 13 times for every 8 orbits of the Earth, creating a pentagrammic pattern of inferior conjunctions. Credit: Tomruen.

Some objects seem to wander around in the night sky relative to many of the visual points of light. At least one occasionally is present in the early morning [on the left] before sunrise as the Morning Star and after sunset as the Evening Star [on the right], the planet Venus. These wanderers and related objects are subjects for observational astronomy and some are meteors.

By observing many of the wandering lights in the night sky, an occasional occultation of the light of one astronomical object may occur by the intervention of another along a closer astronomical stratum.

An occultation of Venus by the Moon occurred "on the afternoon of October 14", 1874.[56] An earlier such occultation "occurred on May 23, 1587, and is thus recorded by [Tycho Brahe] in his Historia Celestis"[56]. "Thomas Street, in his Astronomia Carolina (A.D. 1661), mentions three occultations by Venus, being two occasions when the planet covered Regulus, and once when there was an occultation of Mars by Venus."[56] "[Thomas Street] describes [the occultation of Mars by Venus] as follows: "1590,. Oct. 2nd, 16h. 24s. Michael Mœstlin observed ♂ eclipsed by ♀.""[56]

"NASA joined the world today in viewing a rare celestial event, one not seen by any person now alive. The "Venus transit" -- the apparent crossing of our planetary neighbor in front of the Sun -- was captured from the unique perspective of NASA's Sun-observing TRACE spacecraft."[57]

"The last "Venus transit" occurred more than a century ago, in 1882, and was used to compute the distance from the Earth to the Sun."[57]

"If people miss the June 8 Venus transit, they will have another chance in 2012 (June 6) [imaged third down on the right]. After that, there will not be another Venus transit until 2117 (December 11)."[57]

A conjunction between Venus and Jupiter is shown in the second image down on the left.

The fourth image down on the right is a diagram of inferior conjunctions of Venus with Earth.

"The planet Venus orbits just over 13 times for every 8 orbits of the Earth, creating a pentagrammic pattern of inferior conjunctions. Each successive inferior conjunction occurs after about 1.6 Earth years and therefore shifts about 144 degrees in the direction opposite the Earth's orbital motion. During each cycle of 8 Earth years, the pentagram precesses about 1.5 degrees in the direction of Earth's orbital motion, reflecting the fact that the Earth:Venus orbital ratio is an approximate ('near') rather than a perfect orbital resonance."[58]

## Astrogeology

Main source: Astrogeology
The planet Venus is shown here rotating in a clockwise motion. Credit: Ironchew and NASA.
A portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. Credit: NASA/JPL.
Magellan radar image is of the "crater farm". Credit: Magellan Team, JPL, NASA.

The rotating globe on the right is the radar surface of Venus using the radar scanner of the Magellan probe.

On the second lower right is an image of a "portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. The viewpoint is located 1,310 kilometers (812 miles) southwest of Gula Mons at an elevation of 0.78 kilometer (0.48 mile). The view is to the northeast with Gula Mons appearing on the horizon. Gula Mons, a 3 kilometer (1.86 mile) high volcano, is located at approximately 22 degrees north latitude, 359 degrees east longitude. The impact crater Cunitz, named for the astronomer and mathematician Maria Cunitz, is visible in the center of the image. The crater is 48.5 kilometers (30 miles) in diameter and is 215 kilometers (133 miles) from the viewer's position. Magellan synthetic aperture radar data is combined with radar altimetry to develop a three-dimensional map of the surface. Rays cast in a computer intersect the surface to create a three-dimensional perspective view. Simulated color and a digital elevation map developed by the U.S. Geological Survey, are used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced at the JPL Multimission Image Processing Laboratory and is a single frame from a video released [on] March 5, 1991, [...]."[59]

Third image down on the right is a Magellan radar image of the "crater farm", showing the craters (clockwise from top left) Danilova, Aglaonice, and Saskia centered at 27 S, 339 E. Aglaonice is 65 km in diameter.

"Three large impact craters with diameters ranging from 37 km (23 mi) to 65 km (40 mi) are visible in the fractured plains. Features typical of meteorite impact craters are also visible. Rough radar-bright ejecta surrounds the perimeter of the craters; terraced inner walls and large central peaks can be seen. Crater floors appear dark because they are smooth and have been flooded by lava. Domes of probable volcanic origin can be seen in the southeastern corner. The domes range in diameter from 1-12 km (0.6-7 mi); some have central pits typical of volcanic shields or cones."[60]

## Volcanoes

Main source: Volcanoes
A portion of the eastern edge of Alpha Regio is displayed in this three-dimensional perspective view of the surface of Venus. Credit: NASA/JPL/United States Geological Survey.
Ubastet Fluctus — lava flows about 500 km across on Venus originate from Derceto Corona (beyond the left border of the image; previously called Ammavaru caldera). Credit: Magellan Project, JPL, NASA.
This is a Magellan radar image of a lava channel on Venus. Credit: Magellan Project, JPL, NASA.
Lava has flowed from the apparent source to the upper left into Alcott crater filling it to its brim. Credit: Magellan Project, JPL, NASA.

"A portion of the eastern edge of Alpha Regio is displayed in this three-dimensional perspective view [on the right] of the surface of Venus. The viewpoint is located at approximately 30 degrees south latitude, 11.8 degrees east longitude at an elevation of 2.4 kilometers (3.8 miles). The view is to the northeast at the center of an area containing seven circular dome-like hills. The average diameter of the hills is 25 kilometers (15 miles) with maximum heights of 750 meters (2,475 feet). Three of the hills are visible in the center of the image. Fractures on the surrounding plains are both older and younger than the domes. The hills may be the result of viscous or thick eruptions of lava coming from a vent on the relatively level ground, allowing the lava to flow in an even lateral pattern. The concentric and radial fracture patterns on their surfaces suggests that a chilled outer layer formed, then further intrusion in the interior stretched the surface. An alternative interpretation is that domes are the result of shallow intrusions of molten lava, causing the surface to rise. If they are intrusive, then magma withdrawal near the end of the eruptions produced the fractures. The bright margins possibly indicate the presence of rock debris or talus at the slopes of the domes. Resolution of the Magellan data is about 120 meters (400 feet). Magellan's synthetic aperture radar is combined with radar altimetry to develop a three-dimensional map of the surface. A perspective view is then generated from the map. Simulated color and a process called radar-clinometry are used to enhance small-scale structures. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the JPL Multimission Image Processing Laboratory."[61]

In the second image on the right is "a 225 meter per pixel Magellan radar image mosaic of Venus, centered at 47 degrees south latitude, 25 degrees east longitude in the Lada region. The scene is approximately 550 kilometers (341 miles) east-west by 630 kilometers (391 miles) north-south. The mosaic shows a system of east-trending radar-bright and dark lava flows encountering and breaching a north-trending ridge belt (left of center). Upon breaching the ridge belt, the lavas pool in a vast, radar-bright deposit (covering approximately 100,000 square kilometers [right side of image]). The source caldera for the lava flows, named Ammavaru, lies approximately 300 kilometers (186 miles) west of the scene."[62]

The third image down on the right is Magellan radar image of a lava channel on Venus. This unusually long channel ranges from Fortuna Tessera in the north down to the eastern Sedna Planitia in the south. The channel is about 2 km wide and shows branches and islands along its length. The framelet shown here is about 50 km wide, and north is up.

On the right, fourth image down, "Magellan's radar system detected few impact craters in the process of being resurfaced by volcanism. Alcott is the largest of these craters in transition, with a diameter of 63 km (39 mi). The trough-like depression (lower left) is a rille through which lava once flowed. A remnant of rough radial ejecta is preserved outside the crater's southeast rim. The presence of partially lava-flooded craters such as this is important to our understanding of the rate of resurfacing on Venus by volcanism."[63]

## Structural geology

Arachnoids are large structures of unknown origin that have been found only on the surface of Venus. Credit: Magellan Team, JPL, NASA.
This Magellan full-resolution images show the northern part of the Akna Montes (mountains) of Venus. Credit: Magellan Team, JPL, NASA.
On this bright, lineated terrain Alpha Regio is a series of troughs, ridges, and faults running in every direction. Credit: Magellan Team, JPL, NASA.
Seven circular domes can be seen on the eastern edge of Alpha Regio. Credit: Magellan Team, JPL, NASA.
The terrain of this region is made up of tessera, which are interlacing ridges and valleys. Credit: USGS.

"Arachnoids are large structures of unknown origin that have been found only on the surface of Venus. Arachnoids get their name from their resemblance to spider-webs. They appear as concentric ovals surrounded by a complex network of fractures, and can span 200 kilometers. Radar echoes from the Magellan spacecraft that orbited Venus from 1990 to 1994 built up this image. Over 30 arachnoids have been identified on Venus, so far. The Arachnoid might be a strange relative to the volcano, but possibly different arachnoids are formed by different processes."[64]

The second image down on the right shows the northern part of the Akna Montes (mountains) of Venus and an apparent impact crater.

"The Akna range is a north-south trending ridge belt that forms the western border of the elevated smooth plateau of Lakshmi Planum (plains). The Lakshmi plateau plains are formed by extensive volcanic eruptions and are bounded by mountain chains on all sides. The plains appear to be deformed near the mountains. This suggests that some of the mountain building activity occurred after the plains formed. An impact crater (Official International Astronomical Union name 'Wanda,' mapped first by the Soviet Venera 15/16 mission in 1984 at low resolution) with a diameter of 22 kilometers (14 miles) was formed by the impact of an asteroid in the Akna mountains. The crater has a rugged central peak and a smooth radar-dark floor, probably volcanic material. The crater does not appear to be much deformed by later crustal movement that uplifted the mountains and crumpled the plains. Material from the adjacent mountain ridge to the west, however, appears to have collapsed into the crater. Small pits seen to the north of the crater may be volcanic collapse pits a few kilometers across (1-2 miles). The ridge of the Akna mountains immediately to the west of the crater is 8 kilometers wide (5 miles). The area imaged is approximately 200 kilometers long and 125 kilometers wide (130 by 80 miles). This area is centered at 71.5 degrees north latitude, 324 degrees east longitude. The resolution of the Magellan radar system is 120 meters (400 feet). At this latitude the radar views the surface from an angle of 23 degrees off vertical, creating a perspective as though a viewer were looking at the scene from the right (east) at an angle of 23 degrees above the surface."[65]

Bright, lineated terrain of Alpha Regio is a series of troughs, ridges, and faults running in every direction in the third image down on the right.

"The lengths of these features range from 10 km (6.3 mi) to 60 km (37 mi). The elevation of Alpha Regio varies over a range of 4 km (2.5 mi). Low-lying areas appear dark in the radar images and may be filled with lava. Volcanoes appear as bright spots on the smooth plains. Notice the large volcano in the upper right. At the center of this 35 km (22 mi) volcano is a caldera; its western edge appears to be either a debris flow or a lava flow. The black square represents missing data."[66]

Seven circular domes are imaged in the fourth down on the right.

"They average 25 km (15 mi) in diameter with maximum heights of 750 m (2475 ft). Some scientists believe they are the result of eruptions of thick lava that flowed from a vent on level ground, resulting in an even lateral pattern of lava. The concentric and radial fracture pattern on the surface of the domes suggests that lava welled up inside the domes, causing the surface to stretch."[67]

This region in the fifth image down on the right is one of the most rugged on Venus. The terrain is made up of tessera, which are interlacing ridges and valleys.

"Venus and the Earth have similar radii and estimated bulk compositions, and both possess an iron core that is at least partially liquid. However, despite these similarities, Venus lacks an appreciable dipolar magnetic field."[68]

This "absence is due to Venus’s also lacking plate tectonics for the past 0.5 b.y. (1 b.y.=109 yr). The generation of a global magnetic field requires core convection, which in turn requires extraction of heat from the core into the overlying mantle. Plate tectonics cools the Earth’s mantle; on the basis of elastic thickness estimates and convection models, [...] the mantle temperature on Venus is currently increasing. This heating will reduce the heat flux out of the core to zero over ~1 b.y., halting core convection and magnetic field generation. If plate tectonics was operating on Venus prior to ca. 0.5 Ga, a magnetic field may also have existed. On Earth, the geodynamo may be a consequence of plate tectonics; this connection between near-surface processes and core magnetism may also be relevant to the generation of magnetic fields on Mars, Mercury and Ganymede."[68]

The lack of an appreciable Earth-like dipolar magnetic field "cannot be explained by the planet's slow rotation".[68]

In "the absence of plate tectonics, the mantle on Venus cannot cool rapidly enough to drive core convection and a geodynamo."[68]

"Planetary magnetic fields are produced by motion in a conductor, usually the planet’s iron core. Such motion may be due to either thermal convection or compositional convection, driven by core solidification".[68]

"The maximum heat flux that can be extracted from the core without thermal convection is given by"[68]

${\displaystyle F_{c}=k\alpha gT/C_{p},}$

"where k and α are the thermal conductivity and expansivity, g is the acceleration due to gravity, T is the core temperature, and Cp is the specific hear capacity. [...] Fc is in the range 11-30 mW·m-2. Thermal convection will cease if the heat being extracted from the core is less than Fc; in the absence of core solidification, the geodynamo will halt. Compositional convection may continue [...], but will certainly halt if the heat flux out of the core drops to zero or below (i.e., the core starts heating up). The rate at which the core loses heat is controlled by the temperature difference between core and mantle and, thus, on the rate at which the mantle is cooling".[68]

## Paleolithic history

This figurine, designated a Mal'ta Venus, was recovered from Upper Paleolithic deposits at Lake Baikal, Siberia. Credit: unknown, photographer José-Manuel Benito.

The paleolithic period dates from around 2.6 x 106 b2k to the end of the Pleistocene around 12,000 b2k.

The figurine photographed above center was recovered from the Upper Paleolithic deposits at Lake Baikal, Siberia.

## Ancient history

The Venus tablet of Ammisaduqa, dated 1581 BC, records the observations of Babylonian astronomers. It refers to Venus as Nin-dar-an-na, or "bright queen of the sky". Credit: .

The ancient history period dates from around 8,000 to 3,000 b2k.

"In antiquity the classical planets were the non-fixed objects visible in the sky, known to various ancient cultures. The classical planets were therefore the Sun and Moon and the five non-earth [[planets] of our solar system closest to the sun (and closest to the Earth); all easily visible without a telescope. They are Mercury, Venus, Mars, Jupiter, and Saturn."[69]

The day of the week for Venus is Friday and its color is white.[70]

Apparently 5102 b2k (before the year [Epoch astronomy] 2000.0), -3102 or 3102 BC, is the historical year assigned to a Hindu table of planets that does not include the classical planet Venus.[71] "Vénus seule ne s'y trouvait pas."[71] "Venus alone is not found there."[72]

"Babylonian astronomy, too, had a four-planet system. In ancient prayers the planets Saturn, Jupiter, Mars, and Mercury are invoked; the planet Venus is missing; and one speaks of "the four-planet system of the ancient astronomers of Babylonia."[73]"[72]

“That the planet Venus is missing will not startle anybody who knows the eminent importance of the four-planet system in the Babylonian astronomy”[73] “Weidner supposes that Venus is missing in the list of planets because “she belongs to a triad with the moon and the sun.””[72]

3581 b2k: "The Venus tablet of Ammisaduqa, dated 1581 BC, shows that the Babylonians understood that the two were a single object, referred to in the tablet as the "bright queen of the sky," and could support this view with detailed observations.[74]"[12]

"The Greeks thought of the two as separate stars, Phosphorus and Hesperus, until the time of Pythagoras in the sixth century BC.[75]"[12]

"The Romans designated the morning aspect of Venus as Lucifer, literally "Light-Bringer", and the evening aspect as Vesper"[12].

## Classical history

The classical history period dates from around 2,000 to 1,000 b2k.

## Imperial Antiquity

Venus standing on a quadriga of elephants is a Roman frecso from the Officina di Verecundus (IX 7, 5) in Pompeii. Credit: unknown.
A 2nd-century sculpture of the Moon-goddess Selene accompanied by perhaps Phosphorus and Hesperus: the corresponding Latin names are Luna, Lucifer and Vesper. Credit: unknown.

In Felix Romuliana, "the construction [...] is [...] Imperial Antique (1st-3rd c.), and sometimes even late Hellenistic, [in] appearance."[76]

On the left is a Roman fresca of Venus standing on a quadriga of elephants from the Officina di Verecundus (IX 7, 5) in Pompeii, first century.

A 2nd-century sculpture on the right perhaps shows Phosphorus (the Morning star) and Hesperus (the Evening star) on either side of the Moon (Selene or Luna).

## Recent history

Main sources: History/Recent and Recent history
Illustration of Lucifer is in the first fully illustrated print edition of Dante Alighieri's Divine Comedy. Woodcut for Inferno, canto 33. Pietro di Piasi, Venice, 1491. Credit: Petrus de Plasiis.
Hesperus is the Personification of the Evening, Palacete de la Moncloa, Madrid, 1765. Credit: Anton Raphael Mengs.
Eos, Phosphoros, Hesperos, Helios, are shown in a black-coloured pencil drawing, The National Museum in Warsaw, 1897. Credit: Stanisław Wyspiański.
The castration of Saturn and the birth of Venus on the left is depicted. Credit: medieval copyist.
This is a tempera on panel of The Birth of Venus. Credit: Sandro Botticelli.
This painting depicts The birth of Venus. Credit: Giorgio Vasari.
This is an oil on canvas of The Birth of Venus. Credit: Pierre Charles Trémolières.
This is an oil on canvas of The Birth of Venus. Credit: Alexandre Cabanel.
This oil on canvas painting is of The Birth of Venus. Credit: William-Adolphe Bouguereau.
The Toilet of Venus (“The Rokeby Venus”) has Venus almost reclining like the top prehistoric comet-like figurine. Credit: Diego Velázquez.

The recent history period dates from around 1,000 b2k to present.

Lucifer (the morning star) is depicted on the top right from 1491.

Hesperus is the Greek name for the Evening star shown in the painting on the left from 1765 and on the right from 1897.

Phosphorus is a Greek name for the Morning star shown in a black-coloured pencil drawing from 1897 on the lower right.

The second image down on the left is a medieval copyist of the castration of Saturn producing the birth of Venus. The medieval period lasted from about 1600 b2k to 600 b2k.

The third image down on the right is a tempera on panel by Sandro Botticelli from circa 1485 (about 515 b2k).

The third image down on the left is a painting by Giorgio Vasari depicting the The Birth of Venus from 1555 - 1557.

The fourth image down on the right is an oil on canvas by Pierre Charles Trémolières depicting the The Birth of Venus by 1739.

The fourth image down on the left is an oil on canvas by Alexandre Cabanel depicting the The Birth of Venus from 1863.

The fifth image down on the right is an 1897 oil on canvas interpretation of the birth of Venus by William-Adolphe Bouguereau.

Three images show Venus in a comet-like manner: the fifth down on the left by Diego Velázquez, that by Alexandre Cabanel also on the left, and that by Pierre Charles Trémolières on the right.

## Spacecraft

The Pioneer Venus Orbiter was the first of a two-spacecraft orbiter-probe combination designed to conduct a comprehensive investigation of the atmosphere of Venus. Credit: NASA.

"The Pioneer Venus Orbiter was the first of a two-spacecraft orbiter-probe combination designed to conduct a comprehensive investigation of the atmosphere of Venus. The spacecraft was a solar-powered cylinder about 250 cm in diameter with its spin axis spin-stabilized perpendicular to the ecliptic plane. A high-gain antenna was mechanically despun to remain focused on the earth. The instruments were mounted on a shelf within the spacecraft except for a magnetometer mounted at the end of a boom to ensure against magnetic interference from the spacecraft. Pioneer Venus Orbiter measured the detailed structure of the upper atmosphere and ionosphere of Venus, investigated the interaction of the solar wind with the ionosphere and the magnetic field in the vicinity of Venus, determined the characteristics of the atmosphere and surface of Venus on a planetary scale, determined the planet's gravitational field harmonics from perturbations of the spacecraft orbit, and detected gamma-ray bursts. UV observations of comets have also been made. From Venus orbit insertion on December 4, 1978 to July 1980 periapsis was held between 142 and 253 km to facilitate radar and ionospheric measurements. Thereafter, the periapsis was allowed to rise (to 2290 km at maximum) and then fall, to conserve fuel. In May 1992 Pioneer Venus began the final phase of its mission, in which the periapsis was held between 150 and 250 km until the fuel ran out and atmospheric entry destroyed the spacecraft the following August."[77]

## Hypotheses

Main source: Hypotheses
1. Venus has been added between the Earth and the Sun in recorded history.
2. The atmosphere of Venus is that of a volcanic planet.
3. Magnetic field reversals of the Sun occur with the sunspot cycle which may have its origins in enhanced electron currents from Jupiter and Venus when perihelion is coincident.
4. Venus is often confused with Aphrodite (the Moon).
5. Venus has "a core of metallized silicates".[78]
6. Venus has "an iron core".[78]
7. "A chondritic composition of the whole planet" with hypothesis 1.[78]
8. "a chondritic mantle" composition with hypothesis 2.[78]
9. "a uniform distribution of radioactivity" is a stage of the thermal history of Venus.[78]
10. "radioactive elements from the upper 1 000 km were gradually carried out into the crust." is a stage of the thermal history of Venus.[78]
11. "This transport [of radioactive elements begins] at the start of the melting of the mantle".[78]
12. "The mantle of Venus, as that of the Earth [is] a mixture of different minerals and [melts] in some interval of temperatures [...] of the order of 200°."[78]
13. "In the core the melting [occurs] at constant temperature for each given depth."[78]
14. "The core [has] a metallic conductivity independent of the temperature."[78]

"Preliminary estimates by Safronov (1965, 1969) of the initial temperature of the Earth were used to choose initial temperatures of Venus and Mercury."[78]

The "molecular conductivity of amorphous matter does not decrease with temperature (as it does in crystalline bodies)."[78]

The "molecular conductivity ceases to depend on temperature with the onset of melting."[78]

For hypothesis 1, the "core of metallized silicates is liquid at the present moment."[78]

For hypothesis 2, "the core is liquid with temperature 12 400 °K."[78]

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