Venus

Venus is the second planet from Sun in the Solar System. It is also the hottest planet in the Solar System, with a surface temperature of 465°C. It is named after the Roman goddess of love and beauty. It is also the second brightest object after The Moon, reaching a magnitude of -4.6. Venus is sometimes called Earth's "twin planet" because of their similar size, mass, proximity to the Sun, and composition. However, Venus has the densest atmosphere of the four terrestrial planets as well as Venus is also believed to had oceans in the past, but the water evaporated due to increasing luminosity of the Sun. It has a average distance of 108,208,000 kilometres, and a surface temperature of 465°C.
== Physical characteristics ==
=== Orbit ===
Venus revolves around the Sun on an inner orbit as seen from the perspective of the Earth. One solar orbit takes 224.7 Earth days. During this orbit, it is between the Earth and the Sun. The Venus rotation is retrograde, and it rotates backwards, which means one Venus day lasts longer than one Venus year (225 earth days). However, Venus rotates the Sun faster than it rotates about its axis. One Venus day is equivalent to 242 Earth days and has a very small axial tilt (2.7 degrees) towards its orbital plane. The axial tilt of Earth is greater (23.5 degrees). This makes Venus the second planet from the Sun, with a average distance of 108,208,000 kilometres.
=== Size, mass and structure ===
The mass of Venus is 4.868 x 10^24 kg, or 81.5% of Earth's. It's mean density is 5250 kilograms per cubic metre, it is similar to Earth's despite its internal structure. It's diameter of Venus is 12,103 kilometres, because Venus is slightly smaller than Earth. This makes Venus the second largest terrestrial planet in the Solar System. Venus is in many ways similar to Earth in its structure. It has an liquid iron core that is approximately 2,000 miles (3,200 kilometers) in radius. Above that is a rocky mantle, slowly churning due to the planet's interior heat. The surface is a thin outer crust of rock that bulges and moves as Venus' mantle shifts and creates volcanoes. 
=== Surface ===
The surface of Venus consists of hot deserts, large plains, mountains and valleys. The largest plateau is Aphrodite Terra, which is located at the level of the Venus equator and is about as large as Africa. However, Venus is less mountainous than Earth. There are some elevations that reach 11 kilometres in height (Maxwell Montes), but only 10% of the entire surface is mountainous. Much of the surface is taken up by large plains (70%) and lowlands (20%).
Venus had a distinct pattern of volcanic eruptions, possibly there are still active volcanoes on the planet. Certainly, astronomers have discovered cooled off lava streams that are longer than the longest rivers on the Earth. There are also craters on the surface of Venus, although far less than on Mercury. Larger chunks of rock, however, have reached the surface, leaving impact craters in their wake.
== Atmosphere ==
The planet Venus is surronded by a closed cloud layers. Sometimes, it even rains in a inhospitable environment, incompatible with life. However, the rain consists of sulphuric acid, as it never reaches the surface, evaporates the enormous heat. Despite these inhospitable conditions, space probes succeeded in landing the surface and explored the dusty surface. While the Sun can warm the surface, the dense atmosphere of Venus with its layers of haze prevents heat from being released. The atmospheric pressure is 100 times stronger than Earth (also known as Air pressure).
Venus' atmosphere consists mainly of carbon dioxide and sulfur. The thick atmosphere traps the Sun's heat, resulting in surface temperatures of 735 degrees Kelvin (470 degrees Celsius), as the atmosphere has many layers with different temperatures.
== Observations ==
=== Phases ===
Venus is one of the inner planets, as the orbit passes between the Sun and Earth's orbit, despite different observable phases. During the phases of the waxing or waning Venus crescent, the planet can be observed particularly well. At the time of inferior or superior conjunction, the planet is invisible to the Earth. Conjuction refers that various celestial bodies are located along the same longitude. During the inferior conjuction (sequence Earth-Venus-Sun), Venus is at its closest to Earth. Since Venus' night side is turned towards the Earth, it is invisible to the Earth, as Venus will enter the waxing crescent phase, reaching its point of greatest distance. The greater elongation from Venus can observe the planet, because the greatest elongation is merely 48 degrees, while Mercury's elongation is 28 degrees. As a result of this difference, Venus can be seen for a longer period of time after sunset and earlier before sunrise than Mercury. 
=== Transits ===
The Venusian orbit is slightly inclined relative to Earth's orbit; thus, when the planet passes between Earth and the Sun, it usually does not cross the face of the Sun. Transits of Venus occur when the planet's inferior conjunction coincides with its presence in the plane of Earth's orbit. Transits of Venus occur in cycles of 243 years with the current pattern of transits being pairs of transits separated by eight years, at intervals of about 105.5 years or 121.5 years—a pattern first discovered in 1639 by the English astronomer Jeremiah Horrocks. The latest pair was June 8, 2004 and June 5–6, 2012. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions.
The preceding pair of transits occurred in December 1874 and December 1882; the following pair will occur in December 2117 and December 2125. The 1874 transit is the subject of the oldest film known, the 1874 Passage de Venus. Historically, transits of Venus were important, because they allowed astronomers to determine the size of the astronomical unit, and hence the size of the Solar System as shown by Horrocks in 1639. Captain Cook's exploration of the east coast of Australia came after he had sailed to Tahiti in 1768 to observe a transit of Venus.
== Exploration ==
=== Early observation ===
Because the movements of Venus appear to be discontinuous (it disappears due to its proximity to the sun, for many days at a time, and then reappears on the other horizon), some cultures did not recognize Venus as a single entity; instead, they assumed it to be two separate stars on each horizon: the morning and evening star. Nonetheless, a cylinder seal from the Jemdet Nasr period and the Venus tablet of Ammisaduqa from the First Babylonian dynasty indicate that the ancient Sumerians already knew that the morning and evening stars were the same celestial object. In the Old Babylonian period, the planet Venus was known as Ninsi'anna, and later as Dilbat. The name "Ninsi'anna" translates to "divine lady, illumination of heaven", which refers to Venus as the brightest visible "star". Earlier spellings of the name were written with the cuneiform sign si4 (= SU, meaning "to be red"), and the original meaning may have been "divine lady of the redness of heaven", in reference to the colour of the morning and evening sky.
The Chinese historically referred to the morning Venus as "the Great White" (Tàibái 太白) or "the Opener (Starter) of Brightness" (Qǐmíng 啟明), and the evening Venus as "the Excellent West One" (Chánggēng 長庚).
In the second century, in his astronomical treatise Almagest, Ptolemy theorized that both Mercury and Venus are located between the Sun and the Earth. The 11th-century Persian astronomer Avicenna claimed to have observed the transit of Venus, which later astronomers took as confirmation of Ptolemy's theory. In the 12th century, the Andalusian astronomer Ibn Bajjah observed "two planets as black spots on the face of the Sun"; these were thought to be the transits of Venus and Mercury by 13th-century Maragha astronomer Qotb al-Din Shirazi, though this cannot be true as there were no Venus transits in Ibn Bajjah's lifetime.
=== Exploration ===
The first robotic space probe mission to Venus and any planet was Venera 1 of the Soviet Venera program launched in 1961, though it lost contact en route.
The first successful mission to Venus (as well as the world's first successful interplanetary mission) was the Mariner 2 mission by the United States, passing on 14 December 1962 at 34,833 km (21,644 mi) above the surface of Venus and gathering data on the planet's atmosphere.
On 18 October 1967, the Soviet Venera 4 successfully entered as the first to probe the atmosphere and deployed science experiments. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 500 °C (932 °F), determined that the atmosphere was 95% carbon dioxide (CO2), and discovered that Venus's atmosphere was considerably denser than Venera 4's designers had anticipated. The joint Venera 4–Mariner 5 data were analysed by a combined Soviet–American science team in a series of colloquia over the following year, in an early example of space cooperation. 
In 1974, Mariner 10 swung by Venus to bend its path toward Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere. This was the first interplanetary gravity assist ever used, a technique which would be used by later probes, most notably Voyager 1 and 2. In 1975, the Soviet Venera 9 and 10 landers transmitted the first images from the surface of Venus, which were in black and white. In 1982 the first colour images of the surface were obtained with the Soviet Venera 13 and 14 landers. NASA obtained additional data in 1978 with the Pioneer Venus project that consisted of two separate missions: Pioneer Venus Orbiter and Pioneer Venus Multiprobe. 
The successful Soviet Venera program came to a close in October 1983, when Venera 15 and 16 were placed in orbit to conduct detailed mapping of 25% of Venus's terrain (from the north pole to 30°N latitude). Several other missions explored Venus in the 1980s and 1990s, including Vega 1 (1985), Vega 2 (1985), Galileo (1990), Magellan (1994), Cassini–Huygens (1998), and MESSENGER (2006). All except Magellan were gravity assists. Then, Venus Express by the European Space Agency (ESA) entered orbit around Venus in April 2006. Equipped with seven scientific instruments, Venus Express provided unprecedented long-term observation of Venus's atmosphere. ESA concluded the Venus Express mission in December 2014. As of 2020, Japan's Akatsuki is in a highly eccentric orbit around Venus since 7 December 2015, and there are several probing proposals under study by Roscosmos, NASA, ISRO, ESA, and the private sector (e.g. by Rocketlab).
== Habitability ==
Speculation on the possibility of life on Venus's surface decreased significantly after the early 1960s when it became clear that the conditions are extreme compared to those on Earth. Venus's extreme temperature and atmospheric pressure make water-based life as currently known unlikely.
Some scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the cooler, acidic upper layers of the Venusian atmosphere). Such speculations go back to 1967, when Carl Sagan and Harold J. Morowitz suggested in a Nature article that tiny objects detected in Venus's clouds might be organisms similar to Earth's bacteria (which are of approximately the same size).
=== Human presence ===
Venus is the place of the very first interplanetary human presence, mediated through robotic missions, with the first successful landings on another planet and extraterrestrial body other than the Moon. Venus was at the beginning of the space age frequently visited by space probes until the 1990s. Currently in orbit is Akatsuki, and the Parker Solar Probe routinely uses Venus for gravity assist maneuvers.
The only nation that has sent lander probes to the surface of Venus has been the Soviet Union, which has been used by Russian officials to call Venus a "Russian planet".
==== Habitation ====
While the surface conditions of Venus are very inhospitable, the atmospheric pressure and temperature fifty kilometres above the surface are similar to those at Earth's surface. With this in mind the Soviet engineer Sergey Zhitomirskiy (Сергей Житомирский, 1929–2004) in 1971 and more contemporarily NASA aerospace engineer Geoffrey A. Landis in 2003 suggested the use of aerostats for crewed exploration and possibly for permanent "floating cities" in the Venusian atmosphere, an alternative to the popular idea of living on planetary surfaces such as Mars. Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of sulfuric acid in the atmosphere.
== See also ==
* List of planets
* List of Solar System objects
* Terrestrial planet
* Sulfur
* Venus transit (redirect to Transit#Venus transit)
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Category:Solar System
Category:Planets