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Venus

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image (c) ESA

Venus is the second planet from the sun and belongs to the terrestrial planets, sometime Venus is called Earth's sister planet, because both are very similar in size, mass and composition. Venus is named after the Roman goddess of love.

It can usually only be seen a few hours before sunrise or a few hours after sunset and in the ancient the Venus called as "Morning Star" and "Evening Star", because the astronomers thought that it would concern two objects.

Venus sluggishly rotates on its axis once every 243 Earth days, while it orbits the Sun every 225 days - its day is longer than its year. Besides that, Venus rotates retrograde (the Sun would rise in the west), or "backwards" spinning in the opposite direction of its orbit around the Sun.

Atmosphere

The atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets and only trace amounts of water have been detected in the atmosphere but with a pressure at the surface about 90 times that of Earth 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 deg C (750deg F) with temperatures at the surface reaching extremes as great as 500 deg C (930 deg 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 (the cloud cover reflects the majority of the sunlight back into space and Venus is usually the brightest planet in the sky).

Super rotation

The cloud-level atmosphere zips around the planet in the opposite direction from the rotation every four Earth days, driven by constant hurricane-force winds (300 km/h (200 mph)). How this atmospheric "super rotation" forms and is maintained continues to be a topic of scientific investigation. About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 to 500 million years ago.

Surface

More than 1,000 volcanoes or volcanic centers larger than 20 kilometers (12 miles) in diameter dot the surface of Venus. Volcanic flows have produced long, sinuous channels extending for hundreds of kilometers. Venus has two large highland areas: The northern highland is named Ishtar Terra (with the size of Australia) and 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.

Magnetic field

Venus has an iron core about 3,000 kilometers (1,200 miles) in radius. Venus has no global magnetic field, though its core iron content is similar to that of Earth, Venus rotates too slowly to generate the type of magnetic field that Earth has.

The mystery of Venus (lost) Moon

Venus was once thought to possess a moon, named "Neith" after the chief goddess of Sais, Egypt first observed by Giovanni Domenico Cassini in 1672. German astronomers called the moon "Kleinchen" 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 stars that happened to be in the right place at the right time, or maybe even asteroids passing by the planet. Venus is now known to be moonless. [1]

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. [2]

Culture

Venus was known to ancient Babylonians around 1600 BC, and to the Mayan 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".

Spacecrafts

Although we cannot normally see through Venus' thick atmosphere, NASA's Magellan mission to Venus used radar to image the surface, and Galileo used infrared mapping to view mid-level cloud structure.

[1] http://en.wikipedia.org/wiki/Neith_(moon)

[2] http://www.newscientist.com/article.ns?id=dn2843

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