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83-430: The Solar New Year is the beginning of the solar calendar year. This event is observed at different times of year and with varying practices in cultures across the globe. The most common bases chosen to begin a new calendar year are the winter solstice , summer solstice , the spring equinox and the autumnal equinox . South and South-east Asian solar calendars are more formally linked to astronomical events. Some of

166-590: A dust ring-cloud , with a suspected origin either from Venus–trailing asteroids, interplanetary dust migrating in waves, or the remains of the Solar System's original circumstellar disc that formed the planetary system . Earth and Venus have a near orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus). Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average. The path that Venus makes in relation to Earth viewed geocentrically draws

249-454: A pentagram over five synodic periods, shifting every period by 144°. This pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower. When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of 41 million km (25 million mi). Because of

332-458: A supercritical state at Venus's surface. Internally, Venus has a core ,  mantle , and  crust . Venus lacks an internal dynamo, and its weakly induced magnetosphere is caused by atmospheric interactions with the solar wind . Internal heat escapes through active volcanism , resulting in resurfacing instead of plate tectonics . Venus is one of two planets in the Solar System ,

415-451: A 4" telescope. Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent. When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it. Astronomer Edmund Halley calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in

498-414: A Venusian year (243 versus 224.7 Earth days). Slowed by its strong atmospheric current the length of the day also fluctuates by up to 20 minutes. Venus's equator rotates at 6.52 km/h (4.05 mph), whereas Earth's rotates at 1,674.4 km/h (1,040.4 mph). Venus's rotation period measured with Magellan spacecraft data over a 500-day period is smaller than the rotation period measured during

581-459: A change that would have occurred over the course of billions of years. The rotation period of Venus may represent an equilibrium state between tidal locking to the Sun's gravitation, which tends to slow rotation, and an atmospheric tide created by solar heating of the thick Venusian atmosphere. The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5   Venusian solar days (5.001444 to be precise), but

664-561: A depression. These features are volcanic in origin. Most Venusian surface features are named after historical and mythological women. Exceptions are Maxwell Montes, named after James Clerk Maxwell , and highland regions Alpha Regio , Beta Regio , and Ovda Regio . The last three features were named before the current system was adopted by the International Astronomical Union , the body which oversees planetary nomenclature . The longitude of physical features on Venus

747-463: A dynamo at its core. A dynamo requires three things: a conducting liquid, rotation, and convection . The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus's core. On Earth, convection occurs in the liquid outer layer of

830-449: A more massive primary atmosphere from solar nebula have been proposed to explain the enrichment. However, the atmosphere is depleted of radiogenic argon, a proxy for mantle degassing, suggesting an early shutdown of major magmatism. Studies have suggested that billions of years ago, Venus's atmosphere could have been much more like the one surrounding the early Earth, and that there may have been substantial quantities of liquid water on

913-508: Is 81.5% of Earth's, making it the third-smallest planet in the Solar System . Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen . The surface pressure is 9.3 megapascals (93 bars ), and the average surface temperature is 737 K (464 °C; 867 °F), above the critical points of both major constituents and making

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996-519: Is called Ishtar Terra after Ishtar , the Babylonian goddess of love, and is about the size of Australia. Maxwell Montes , the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km (7 mi) above the Venusian average surface elevation. The southern continent is called Aphrodite Terra , after the Greek mythological goddess of love, and is the larger of the two highland regions at roughly

1079-405: Is currently volcanically active, specifically the detection of olivine , a volcanic product that would weather quickly on the planet's surface. This massive volcanic activity is fuelled by a superheated interior, which models say could be explained by energetic collisions from when the planet was young. Impacts would have had significantly higher velocity than on Earth, both because Venus's orbit

1162-483: Is expressed relative to its prime meridian . The original prime meridian passed through the radar-bright spot at the centre of the oval feature Eve, located south of Alpha Regio. After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia . The stratigraphically oldest tessera terrains have consistently lower thermal emissivity than

1245-636: Is far from certain. Studies reported on 26 October 2023 suggest for the first time that Venus may have had plate tectonics during ancient times and, as a result, may have had a more habitable environment , possibly one capable of sustaining life . Venus has gained interest as a case for research into the development of Earth-like planets and their habitability . Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it has 167 large volcanoes that are over 100 km (60 mi) across. The only volcanic complex of this size on Earth

1328-576: Is faster due to its closer proximity to the Sun and because objects would require higher orbital eccentricities to collide with the planet. In 2008 and 2009, the first direct evidence for ongoing volcanism was observed by Venus Express , in the form of four transient localized infrared hot spots within the rift zone Ganis Chasma , near the shield volcano Maat Mons . Three of the spots were observed in more than one successive orbit. These spots are thought to represent lava freshly released by volcanic eruptions. The actual temperatures are not known, because

1411-462: Is formed by sulphur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the clouds consist of approximately 1% ferric chloride . Other possible constituents of the cloud particles are ferric sulfate , aluminium chloride and phosphoric anhydride . Clouds at different levels have different compositions and particle size distributions. These clouds reflect, similar to thick cloud cover on Earth, about 70% of

1494-452: Is induced by an interaction between the ionosphere and the solar wind , rather than by an internal dynamo as in the Earth's core . Venus's small induced magnetosphere provides negligible protection to the atmosphere against solar and cosmic radiation . The lack of an intrinsic magnetic field on Venus was surprising, given that it is similar to Earth in size and was expected to contain

1577-404: Is most likely at least partially liquid because the two planets have been cooling at about the same rate, although a completely solid core cannot be ruled out. The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's. The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km. This is in line with

1660-432: Is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide ( galena ). Although Venus has no seasons, in 2019 astronomers identified a cyclical variation in sunlight absorption by the atmosphere, possibly caused by opaque, absorbing particles suspended in the upper clouds. The variation causes observed changes in the speed of Venus's zonal winds and appears to rise and fall in time with

1743-406: Is speculation on the possibility that life exists in the upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the atmospheric conditions are the most Earth-like in the Solar System, with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and

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1826-420: Is that the absence of a late, large impact on Venus ( contra the Earth's "Moon-forming" impact) left the core of Venus stratified from the core's incremental formation, and without the forces to initiate/sustain convection, and thus a "geodynamo". The weak magnetosphere around Venus means that the solar wind is interacting directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by

1909-459: Is the Big Island of Hawaii. More than 85,000 volcanoes on Venus were identified and mapped. This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the same erosion process. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, whereas

1992-481: Is the third brightest object in Earth's sky after the Moon and the Sun. In 1961, Venus became the target of the first interplanetary flight, Venera 1 , followed by many essential interplanetary firsts , such as the first soft landing on another planet by Venera 7 in 1970. These probes demonstrated the extreme surface conditions, an insight that has informed predictions about global warming on Earth. This finding ended

2075-450: Is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported " unidentified flying object ". As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction ). Venus shows a larger disc and "quarter phase" at its maximum elongations from

2158-417: Is −4.14 with a standard deviation of 0.31. The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun. The planet is bright enough to be seen in broad daylight, but is more easily visible when the Sun is low on the horizon or setting. As an inferior planet , it always lies within about 47° of

2241-482: The Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks, a " Venus snow " that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance

2324-464: The Sun . Venus "overtakes" Earth every 584 days as it orbits the Sun. As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Although Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it

2407-401: The decreasing eccentricity of Earth's orbit , the minimum distances will become greater over tens of thousands of years. From the year   1 to 5383, there are 526 approaches less than 40 million km (25 million mi); then, there are none for about 60,158 years. While Venus approaches Earth the closest, Mercury is more often the closest to Earth of all planets. Venus has

2490-422: The dissociation of water molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind could have led to

2573-415: The sulphur in the atmosphere may indicate that there have been recent eruptions. About 80% of the Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains. Two highland "continents" make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent

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2656-417: The tropical year , usually either the mean tropical year or the vernal equinox year . The following are tropical solar calendars: Every one of these calendars has a year of 365 days, which is occasionally extended by adding an extra day to form a leap year , a method called " intercalation ", the inserted day being "intercalary". The Baháʼí calendar , another example of a solar calendar, always begins

2739-404: The zodiacal constellation near which the Sun can be found. A calendar of this type is called a sidereal solar calendar . The mean calendar year of such a calendar approximates the sidereal year . Leaping from one lunation to another, but one Sidereal year is the period between two occurrences of the sun, as measured by the stars' solar calendar, which is derived from the Earth's orbit around

2822-492: The 16-year period between the Magellan spacecraft and Venus Express visits, with a difference of about 6.5   minutes. Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury 's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath

2905-558: The Earth in its orbit [the number of days of Mercury's synodic orbital period]). One Venusian year is about 1.92   Venusian solar days. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface. Venus may have formed from the solar nebula with a different rotation period and obliquity, reaching its current state because of chaotic spin changes caused by planetary perturbations and tidal effects on its dense atmosphere,

2988-457: The Earth. The Islamic calendar is a purely lunar calendar and has a year, whose start drifts through the seasons and so is not a solar calendar. The Maya Tzolkin calendar, which follows a 260-day cycle, has no year, therefore it is not a solar calendar. Also, any calendar synchronized only to the synodic period of Venus would not be solar. Lunisolar calendars may be regarded as solar calendars, although their dates additionally indicate

3071-487: The Sun and thus receives only 25% of Mercury's solar irradiance , of 2,600 W/m (double that of Earth). Because of its runaway greenhouse effect , Venus has been identified by scientists such as Carl Sagan as a warning and research object linked to climate change on Earth. Venus's atmosphere is rich in primordial noble gases compared to that of Earth. This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact or accretion of

3154-470: The Sun's 11-year sunspot cycle . The existence of lightning in the atmosphere of Venus has 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. According to these measurements,

3237-422: The Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it. The phases are clearly visible in

3320-590: The Venusian surface is estimated to be 300–600   million years old. Several lines of evidence point to ongoing volcanic activity on Venus. Sulfur dioxide concentrations in the upper atmosphere dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold. This may mean that levels had been boosted several times by large volcanic eruptions. It has been suggested that Venusian lightning (discussed below) could originate from volcanic activity (i.e. volcanic lightning ). In January 2020, astronomers reported evidence that suggests that Venus

3403-411: The atmosphere before reaching the ground. Without data from reflection seismology or knowledge of its moment of inertia , little direct information is available about the internal structure and geochemistry of Venus. The similarity in size and density between Venus and Earth suggests that they share a similar internal structure: a core , mantle , and crust . Like that of Earth, the Venusian core

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3486-474: The atmosphere of Venus. On 29 January 2013, ESA scientists reported that the ionosphere of Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions." In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of

3569-443: The atmosphere. Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide, or found that in fact there was no absorption line. Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the planet's two hemispheres, those facing and not facing the Sun, despite Venus's slow rotation. Winds at

3652-512: The carbon dioxide air. Venus's atmosphere could also have a potential thermal habitable zone at elevations of 54 to 48 km, with lower elevations inhibiting cell growth and higher elevations exceeding evaporation temperature. The putative detection of an absorption line of phosphine in Venus's atmosphere, with no known pathway for abiotic production, led to speculation in September 2020 that there could be extant life currently present in

3735-412: The closest in mass and size to its orbital neighbour Earth . Venus has by far the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover. At the surface it has a mean temperature of 737 K (464 °C; 867 °F) and a pressure 92 times that of Earth's at sea level. These extreme conditions compress carbon dioxide into

3818-420: The core because the bottom of the liquid layer is much higher in temperature than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced heat flux through the crust. This insulating effect would cause the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead,

3901-552: The crust. Then, over a period of about 100   million years, subduction occurs on an enormous scale, completely recycling the crust. Venusian craters range from 3 to 280 km (2 to 174 mi) 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 so much by the atmosphere that they do not create an impact crater. Incoming projectiles less than 50 m (160 ft) in diameter will fragment and burn up in

3984-455: The currents and drag of its atmosphere. It takes 224.7 Earth days for Venus to complete an orbit around the Sun, and a Venusian solar year is just under two Venusian days long. The orbits of Venus and Earth are the closest between any two Solar System planets, approaching each other in synodic periods of 1.6 years. Venus and Earth have the lowest difference in gravitational potential of any pair of Solar System planets. This allows Venus to be

4067-412: The daytime with overcast clouds". Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days. Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed. The surface of Venus is effectively isothermal ; it retains a constant temperature not only between the two hemispheres but between

4150-579: The daytime. French emperor Napoleon Bonaparte once witnessed a daytime apparition of the planet while at a reception in Luxembourg . Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington, D.C., on 4   March 1865. A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction . Since

4233-578: The early solar system orbital dynamics have shown that the eccentricity of the Venus orbit may have been substantially larger in the past, reaching values as high as 0.31 and possibly impacting early climate evolution. All planets in the Solar System orbit the Sun in an anticlockwise direction as viewed from above Earth's north pole. Most planets rotate on their axes in an anticlockwise direction, but Venus rotates clockwise in retrograde rotation once every 243 Earth days—the slowest rotation of any planet. This Venusian sidereal day lasts therefore longer than

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4316-442: The equator and the poles. Venus's minute axial tilt —less than 3°, compared to 23° on Earth—also minimizes seasonal temperature variation. Altitude is one of the few factors that affect Venusian temperatures. The highest point on Venus, Maxwell Montes , is therefore the coolest point on Venus, with a temperature of about 655 K (380 °C; 715 °F) and an atmospheric pressure of about 4.5 MPa (45 bar). In 1995,

4399-415: The existence of perhaps the largest stationary gravity waves in the solar system. Venus orbits the Sun at an average distance of about 0.72  AU (108 million  km ; 67 million  mi ), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical , Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01. Simulations of

4482-621: The first observation-based estimate of 3,500 km. The principal difference between the two planets is the lack of evidence for plate tectonics on Venus, possibly because its crust is too strong to subduct without water to make it less viscous . This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field . Instead, Venus may lose its internal heat in periodic major resurfacing events. In 1967, Venera 4 found Venus's magnetic field to be much weaker than that of Earth. This magnetic field

4565-465: The following 200 years , but most were determined to be stars in the vicinity. Alex Alemi's and David Stevenson 's 2006 study of models of the early Solar System at the California Institute of Technology shows Venus likely had at least one moon created by a huge impact event billions of years ago. About 10   million   years later, according to the study, another impact reversed

4648-429: The heat from the core is reheating the crust. One possibility is that Venus has no solid inner core, or that its core is not cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already been completely solidified. The state of the core is highly dependent on the concentration of sulphur , which is unknown at present. Another possibility

4731-399: The hypothesis of a spin-orbit resonance with Earth has been discounted. Venus has no natural satellites. It has several trojan asteroids : the quasi-satellite 524522 Zoozve and two other temporary trojans, 2001 CK 32 and 2012 XE 133 . In the 17th century, Giovanni Cassini reported a moon orbiting Venus, which was named Neith and numerous sightings were reported over

4814-516: The impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called " farra ", which look somewhat like pancakes and range in size from 20 to 50 km (12 to 31 mi) across, and from 100 to 1,000 m (330 to 3,280 ft) high; radial, star-like fracture systems called "novae"; features with both radial and concentric fractures resembling spider webs, known as " arachnoids "; and "coronae", circular rings of fractures sometimes surrounded by

4897-402: The lightning rate is at least half that on Earth, however other instruments have not detected lightning at all. The origin of any lightning remains unclear, but could originate from clouds or Venusian volcanoes . In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole. Venus Express discovered, in 2011, that an ozone layer exists high in

4980-492: The loss of most of Venus's water during the first billion years after it formed. However, the planet may have retained a dynamo for its first 2–3 billion years, so the water loss may have occurred more recently. The erosion has increased the ratio of higher-mass deuterium to lower-mass hydrogen in the atmosphere 100 times compared to the rest of the solar system. Venus has a dense atmosphere composed of 96.5% carbon dioxide , 3.5% nitrogen—both exist as supercritical fluids at

5063-514: The lowest gravitational potential difference to Earth than any other planet, needing the lowest delta-v to transfer between them. Tidally Venus exerts the third strongest tidal force on Earth, after the Moon and the Sun, though significantly less. To the naked eye , Venus appears as a white point of light brighter than any other planet or star (apart from the Sun). The planet's mean apparent magnitude

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5146-399: The moon phase. Typical lunisolar calendars have years marked with a whole number of lunar months, so they can not indicate the position of Earth relative to the Sun with the same accuracy as a purely solar calendar. The following is a list of current, historical, and proposed solar calendars: Venus Venus is the second planet from the Sun . It is a terrestrial planet and is

5229-544: The more widely known solar new year celebrations include: Solar calendar The Egyptians appear to have been the first to develop a solar calendar, using as a fixed point the annual sunrise reappearance of the Dog Star— Sirius , or Sothis—in the eastern sky, which coincided with the annual flooding of the Nile River. They constructed a calendar of 365 days, consisting of 12 months of 30 days each, with 5 days added at

5312-420: The most accessible destination and a useful gravity assist waypoint for interplanetary flights from Earth. Venus figures prominently in human culture and in the history of astronomy. Orbiting inferiorly (inside of Earth's orbit), it always appears close to the Sun in Earth's sky, as either a "morning star" or an "evening star". While this is also true for Mercury , Venus appears more prominent, since it

5395-404: The orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit of Venus above Earth. Consequently, Venus transits above Earth only occur when an inferior conjunction takes place during some days of June or December, the time where the orbits of Venus and Earth cross a straight line with

5478-437: The other being Mercury , that have no moons . Conditions perhaps favourable for life on Venus have been identified at its cloud layers. Venus may have had liquid surface water early in its history with a habitable environment , before a runaway greenhouse effect evaporated any water and turned Venus into its present state. The rotation of Venus has been slowed and turned against its orbital direction ( retrograde ) by

5561-405: The planet underwent a global resurfacing event 300–600   million years ago, followed by a decay in volcanism. Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens

5644-421: The planet's spin direction and the resulting tidal deceleration caused the Venusian moon gradually to spiral inward until it collided with Venus. If later impacts created moons, these were removed in the same way. An alternative explanation for the lack of satellites is the effect of strong solar tides, which can destabilize large satellites orbiting the inner terrestrial planets. The orbital space of Venus has

5727-581: The planet's surface with a density 6.5% that of water —and traces of other gases including sulphur dioxide . The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km ( 5 ⁄ 8  mi) under Earth's ocean surfaces. The density at the surface is 65 kg/m (4.1 lb/cu ft), 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO 2 -rich atmosphere generates

5810-466: The position of the Earth in its orbit around the Sun is reckoned with respect to the Equinox , the point at which the orbit crosses the celestial equator, then its dates accurately indicate the seasons , that is, they are synchronized with the declination of the Sun. Such a calendar is called a tropical solar calendar . The duration of the mean calendar year of such a calendar approximates some form of

5893-442: The size of South America. A network of fractures and faults covers much of this area. There is recent evidence of lava flow on Venus (2024), such as flows on Sif Mons, a shield volcano, and on Niobe Planitia, a flat plain. There are visible calderas . The planet has few impact craters , demonstrating that the surface is relatively young, at 300–600   million years old. Venus has some unique surface features in addition to

5976-523: The size of the hot spots could not be measured, but are likely to have been in the 800–1,100 K (527–827 °C; 980–1,520 °F) range, relative to a normal temperature of 740 K (467 °C; 872 °F). In 2023, scientists reexamined topographical images of the Maat Mons region taken by the Magellan orbiter. Using computer simulations, they determined that the topography had changed during an 8-month interval, and concluded that active volcanism

6059-410: The strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F). This makes the Venusian surface hotter than Mercury 's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), even though Venus is nearly twice Mercury's distance from

6142-456: The sun every 28 years. Indian calendars like the Hindu calendar , Tamil calendar , Bengali calendar (revised) and Malayalam calendar are sidereal solar calendars. The Thai solar calendar when based on the Hindu solar calendar was also a sidereal calendar. They are calculated on the basis of the apparent motion of the Sun through the twelve zodiacal signs rather than the tropical movement of

6225-443: The sunlight that falls on them back into space, and since they cover the whole planet they prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface, resulting in average daytime levels of illumination at the surface of 14,000 lux , comparable to that on Earth "in

6308-459: The surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen. Above the dense CO 2 layer are thick clouds, consisting mainly of sulfuric acid , which

6391-489: The surface atmosphere a supercritical fluid out of mainly supercritical carbon dioxide and some supercritical nitrogen. The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and

6474-503: The surface. After a period of 600 million to several billion years, solar forcing from rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water and the current atmosphere. A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was added to its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there

6557-420: The surrounding basaltic plains measured by Venus Express and Magellan , indicating a different, possibly a more felsic , mineral assemblage. The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics , implying that habitable condition had existed on early Venus with large bodies of water at some point. However, the nature of tessera terrains

6640-487: The theories and then popular science fiction about Venus being a habitable or inhabited planet. Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. It is similar to Earth in size and mass and is often described as Earth's "sister" or "twin". Venus is close to spherical due to its slow rotation. Venus has a diameter of 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth's—and its mass

6723-405: The year on the vernal equinox and sets its intercalary days so that the following year also begins on the vernal equinox. The moment of the vernal equinox in the northern hemisphere is determined using the location of Tehran "by means of astronomical computations from reliable sources". If the position of the Earth (see above) is reckoned with respect to the fixed stars, then the dates indicate

6806-540: The year’s end. The Egyptians’ failure to account for the extra fraction of a day, however, caused their calendar to drift gradually into error. The oldest solar calendars include the Julian calendar and the Coptic calendar . They both have a year of 365 days, which is extended to 366 once every four years, without exception, so have a mean year of 365.25 days. As solar calendars became more accurate, they evolved into two types. If

6889-458: Was the cause. Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates

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