Information AboutVenus |
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Venus is the second Planet from the Sun . A Terrestrial Planet , it is sometimes called Earth 's "sister planet", as the two are very similar in size and bulk composition. Name Venus is named after the Roman Goddess of love. The adjective ''Venusian'' is commonly used for Venus, but the '', which is avoided because of its modern association with Sexually Transmitted Disease s. Some astronomers use '' Cytherea n'', which comes from Cytherea , another name for Aphrodite in ancient Greek Mythology . Other less common adjectives include ''Venerean'', ''Venerian'', and ''Veneran''. The Chinese , Korean , Japan ese and Vietnam ese cultures refer to the planet as the ''metal star'', 金星, based on the Five Elements . Orbital characteristics Orbit Although all planets' Orbits are Elliptical , Venus's orbit is the closest to Circular , with an Eccentricity of less than 1%. As Venus is closer to the Sun than the Earth is, it always appears in roughly the same direction from Earth as the Sun (the greatest Elongation is 47.8°), so on Earth it can usually only be seen a few hours before sunrise or a few hours after sunset. However, when at its brightest, Venus may be seen during the daytime, making it the only heavenly body that can be seen both day and night besides the Moon (except for the occasional Nova , such as the one that created the Crab Nebula ). It is sometimes referred to as the " Morning Star " or the " Evening Star ", and when it is visible in dark skies it is by far the brightest object in the sky (besides the Moon). Brian Tung wrote: :The Greeks, in fact, had two different names for Venus. They called its morning apparition, or appearance, Phosphoros (Greek for light-bringer, which the Romans transformed into Lucifer), and they called its evening apparition, Hesperos (Greek for west, which the Romans transformed into Vesper). It took the Greek philosopher and mathematician Pythagoras (c. 560-480 B.C.) to realize they were one and the same planet, although he may have gotten the idea from the Babylonians. {Link without Title}
At inferior conjunction, Venus can get closer to earth than any other planet--little more than 100 times the Moon's average distance. On December 16th, 1850, Venus reached the lowest distance to earth since 1800, with a value of 0.26413854 AU = 39,514,827 kilometers. This will be the closest approach of Venus to Earth until December 16th, 2101 when Venus will reach a distance of 0.26431736 AU = 39,514,578 kilometers to earth. Rotation Venus has a slow Retrograde Rotation , meaning it rotates from east to west, instead of west to east as most of the other major planets do. ( Pluto and Uranus also have retrograde rotation, though Uranus's axis, tilted at 97.86 degrees, almost lies in its orbital plane.) A slow retrograde rotation is thought to have developed as a consequence of tidal forces, friction, and solar heating of Venus' thick atmosphere. {Link without Title} If the Sun could be seen from Venus' surface, it would appear to rise in the west and set in the east for a day-night cycle of 116.75 Earth days (Venus' mean solar day), and a Venusian year would thus last 1.92 Venusian "days". At the equator, Venus' surface rotates at a mere 6.5 km/h (4 mph). In addition to this unusual retrograde rotation, the periods of Venus' rotation and of its orbit are synchronized in such a way that it always presents the same face toward Earth when the two planets are at their closest approach (5.001 Venusian solar days between each inferior Conjunction ). This may simply be a coincidence, but there is some speculation that this may be the result of Tidal Locking , with Tidal Force s affecting Venus' rotation whenever the planets get close enough together —although the tides raised by Venus on Earth are vanishingly small. Physical characteristics Atmosphere ( February 26 , 1979 ). The immense C- or Y-shaped features which are visible only in these wavelengths are individually short lived, but reform often enough to be considered a permanent feature of Venus' clouds.]] Venus has an Atmosphere consisting mainly of Carbon Dioxide and a small amount of Nitrogen , with a pressure at the surface about 90 times that of Earth (a pressure equivalent to a depth of 1 kilometer under Earth's Ocean s); its atmosphere is also roughly 90 times more massive than ours. This enormously CO2-rich atmosphere results in a strong Greenhouse Effect that raises the surface temperature more than 400 °C (750 °F) with temperatures at the surface reaching extremes as great as 500 °C (930 °F) in low elevation regions near the planet's equator. This makes Venus's surface hotter than Mercury 's, even though Venus is nearly twice as distant from the Sun and only receives 25% of the solar Irradiance (2613.9 W/m&2 in the upper atmosphere, and just 1071.1 W/m&2 at the surface). Owing to the thermal inertia and convection of its dense atmosphere, the temperature does not vary significantly between the night and day sides of Venus, despite its extremely slow rotation. Upper atmosphere winds circling the planet approximately every 4 Earth-days help distribute the heat to other areas on the surface. The solar irradiance is so much lower at the surface of Venus because the planet's thick cloud cover reflects the majority of the sunlight back into space. This prevents most of the sunlight from ever heating the surface. Venus's Bolometric Albedo is approximately 60%, and its visual light albedo is even greater. Thus, despite being closer to the Sun than Earth, the surface of Venus is not as well heated and even less well lit by the Sun. In the absence of any greenhouse effect, the temperature at the surface of Venus would be quite similar to Earth. A common conceptual misunderstanding regarding Venus is the mistaken belief that its thick cloud cover traps heat, as the opposite is actually true. The cloud cover keeps the planet much cooler than it would be otherwise. The immense quantity of CO2 in the atmosphere is what traps the heat by the greenhouse mechanism. (left to right): Mercury , Venus, Earth , and Mars .]] There are strong 300 km/h (200 mph) winds at the cloud tops, but winds at the surface are very slow, no more than a few miles per hour. However, owing to the high density of the atmosphere at Venus's surface, even such slow winds exert a significant amount of force against obstructions. The clouds are mainly composed of Sulfur Dioxide and Sulfuric Acid droplets and cover the planet completely, obscuring any surface details from the Human Eye . The temperature at the tops of these clouds is approximately −45 °C (−50 °F). The mean surface temperature of Venus, as given by NASA , is 864 °F (464 °C) . The minimal value of the temperature, listed in the table, refers to cloud tops —the surface temperature is never below 400 °C (750 °F). (This makes the surface temperature hot enough to melt Lead .) The atmosphere also contains Hydrogen Sulfide (H2S) and Carbonyl Sulfide (COS). Hydrogen sulfide reacts with Sulfur Dioxide , which implies that some process must be creating these components. It is unclear how the carbonyl sulfide could be formed--it is often a sign of biological activity. Some have suggested that microbes exist in the clouds (which also contain droplets of water), and produce these components from water, Carbon Monoxide and Sulfur Dioxide . New Scientist, Sept. 28, 2002, p. 16 Surface features image of the surface of Venus, centered at 180 degrees east longitude.]] lander]] Venus has two major continent-like highlands on its surface, rising over vast plains. The northern highland is named Ishtar Terra and has Venus's highest mountains, named the Maxwell Montes (roughly 2 km taller than Mount Everest ) after James Clerk Maxwell , which surround the plateau Lakshmi Planum . Ishtar Terra is about the size of Australia . In the southern hemisphere is the larger Aphrodite Terra , about the size of South America . Between these highlands are a number of broad depressions, including Atalanta Planitia, Guinevere Planitia, and Lavinia Planitia. With the exception of Maxwell Montes, all surface features on Venus are named after real or mythological females. Venus' thick atmosphere causes Meteor s to decelerate as they fall toward the surface, and even large meteors will strike the surface at too low a speed to form an Impact Crater if they have less than a certain threshold Kinetic Energy . Smaller objects also break up in the dense atmosphere before hitting the ground, and thus no impact crater smaller than about 3 km (2 mi) in diameter can form. Nearly 90% of Venus's surface appears to consist of recently (in the geological sense) solidified core about 3000 km in radius, with a molten rocky mantle making up the majority of the planet. Recent results from the Magellan gravity data indicate that Venus's crust is stronger and thicker than had previously been assumed. It is theorized that Venus does not have mobile Plate Tectonics as Earth does, but instead undergoes massive volcanic upwellings at regular intervals that inundate its surface with fresh lava. Other recent findings suggest that Venus is still volcanically active in isolated Geological Hotspots . Venus's intrinsic Magnetic Field has been found very weak compared to other planets in the solar system. This may be due to its slow rotation being insufficient to drive an internal Dynamo of liquid iron. As a result, Solar Wind strikes Venus's upper atmosphere without mediation. It is thought that Venus originally had as much Water as Earth, but that water vapor in the upper atmosphere was split into Hydrogen and Oxygen due to solar wind. Therefore, the hydrogen escaped into space because of its low molecular mass; the ratio of hydrogen to Deuterium (a heavier Isotope of hydrogen which doesn't escape as quickly) in Venus's atmosphere seems to support this theory. Molecular oxygen is thought to have combined with atoms in the crust (large amounts of oxygen, however, remain in the atmosphere in the form of Carbon Dioxide ). Because of dryness, Venus's rocks are much harder than Earth's, which leads to steeper mountains, cliffs and other features. Venus has had substantial volcanism in its history and there is little erosion, leading to the basaltic lava surface. Venus' moon Venus was once thought to possess a Moon , named Neith after the chief goddess of Sais , Egypt (whose veil no mortal raised), first observed by Giovanni Domenico Cassini in 1672 . German astronomers called the moon Kleinchen (literally "tiny"), and sporadic sightings by astronomers continued until 1892 . These sightings have since been discredited, and are thought to have been either spurious internal reflections, mostly faint Star s that happened to be in the right place at the right time, or maybe even Asteroid s passing by the planet. Venus is now known to be moonless. Observations and explorations of Venus See Also: Observations and explorations of Venus Venus sky movement patterns have been observed several times within the past 4000 years by a number of people, including the Greeks . For elongations and other aspects, see Aspects Of Venus . Life on Venus Space probes in the 1960's made it clear that the surface of Venus is far too hot to support life as we know it. The atmosphere is also lacking in oxygen and water vapor. However, temperatures are much lower at the high altitudes of the cloud layer. In 1961, Carl Sagan proposed that the clouds could be seeded with algae, in an attempt to terraform the planet. Some speculate that spores from Earth could hitch a ride on small passing asteroids and survive a trip to Venus's atmosphere. The sensational idea that life could exist in the Venusian clouds has been proposed repeatedly. {Link without Title} {Link without Title} However, the likelihood of life on Venus, even in the clouds, has been refuted by a recent National Academy task group, formed to study the necessity of sterilizing Venus probes. {Link without Title} Venus in human culture Mythology The Pentagram has long been associated with the planet Venus and the worship of The Goddess . It is most likely to have originated from the observations of prehistoric astronomers. When viewed from Earth, the successive conjunctions of Venus plot the points of a pentagram around the Sun in an eight-year cycle ''(see Orbit )''. Venus was known to ancient Babylon ians around 1600 BC , and to the Maya n civilization (the Mayans developed a religious calendar based on Venus's motion) and must have been known long before in prehistoric times, given that it is the third brightest object in the sky after the Sun and Moon . The Maasai people in Africa named the planet Kileken , and have a myth about it called "The Orphan Boy." The Morning Star was called the Bearer of Light ("phōsphoros" or "eōsphoros" in Greek and " Lucifer " in Latin, a term later used of the fallen angel cast out of heaven, see Isaiah 14:12). To the Jews it is known as ''Noga'' ("shining"), ''Ayeleth-ha-Shakhar'' ("deer of the dawn") and ''Kochav-ha-'Erev'' ("star of the evening"). Its , and in ancient alchemy stood for Copper . Alchemists constructed the symbol from a circle (representing Spirit ) above a cross (representing Matter ). The association with sex and femininity is supposed to relate to the period of 266 days between the Conjunction and maximum Elongation of Venus, which corresponds more or less to the length of human pregnancy. Fiction See Also: Venus in fiction Until it was penetrated by probes, Venus's opaque cloud layer gave Science Fiction writers free rein in imagining the planet's surface, and they frequently imagined it to be Earthlike. There are some religious sects who believe that Hell may be located on Venus. Its extremely high surface temperature and impenetrable cloud cover cause people to believe that the fires of Hell burn on the surface, obscured from our earthly view. Conversely, other sects consider Venus to be some form of paradise or an advanced secret base for angels/aliens to operate from.
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