分享金星的背景知识

Astronomers refer to Venus as Earth's sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula. However, during the last few years scientists have found that the kinship ends here. Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid droplets. At the surface, the atmospheric pressure is 92 times that of the Earth's at sea-level.

Venus is scorched with a surface temperature of about 482° C (900° F). This high temperature is primarily due to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury.

A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. To an observer on Venus, the Sun would rise in the west and set in the east.

Until just recently, Venus' dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA's Pioneer Venus mission (1978), the Soviet Union's Venera 15 and 16 missions (1983-1984), and NASA's Magellan radar mapping mission (1990-1994). As these spacecraft began mapping the planet a new picture of Venus emerged.

Venus' surface is relatively young geologically speaking. It appears to have been completely resurfaced 300 to 500 million years ago. Scientists debate how and why this occurred. The Venusian topography consists of vast plains covered by lava flows and mountain or highland regions deformed by geological activity. Maxwell Montes in Ishtar Terra is the highest peak on Venus. The Aphrodite Terra highlands extend almost half way around the equator. Magellan images of highland regions above 2.5 kilometers (1.5 miles) are unusually bright, characteristic of moist soil. However, liquid water does not exist on the surface and cannot account for the bright highlands. One theory suggests that the bright material might be composed of metallic compounds. Studies have shown the material might be iron pyrite (also know as "fools gold"). It is unstable on the plains but would be stable in the highlands. The material could also be some type of exotic material which would give the same results but at lower concentrations.

Venus is scarred by numerous impact craters distrubuted randomly over its surface. Small craters less that 2 kilometers (1.2 miles) are almost non-existent due to the heavy Venusian atmosphere. The exception occurs when large meteorites shatter just before impact, creating crater clusters. Volcanoes and volcanic features are even more numerous. At least 85% of the Venusian surface is covered with volcanic rock. Hugh lava flows, extending for hundreds of kilometers, have flooded the lowlands creating vast plains. More than 100,000 small shield volcanoes dot the surface along with hundreds of large volcanos. Flows from volcanos have produced long sinuous channels extending for hundreds of kilometers, with one extending nearly 7,000 kilometers (4,300 miles).

Giant calderas more than 100 kilometers (62 miles) in diameter are found on Venus. Terrestrial calderas are usually only several kilometers in diameter. Several features unique to Venus include coronae and arachnoids. Coronae are large circular to oval features, encircled with cliffs and are hundreds of kilometers across. They are thought to be the surface expression of mantle upwelling. Archnoids are circular to elongated features similar to coronae. They may have been caused by molten rock seeping into surface fractures and producing systems of radiating dikes and fractures

金星上面的crater

General Characteristics

Impact craters are found to be distributed randomly but uniformly over the surface of Venus. Cratering of the terrestrial planets shows a record of two distinct periods, one from the late period of heavy bombardment and the other from a bombardment of asteroids and comets which occured more recently. Venus shows no record of the heavy bombardment period, indicating that it was resurface about 300 to 500 million years ago. The majority of Venusian craters appears pristine because they were formed after Venus was resurfaced; there has been very little geologic activity and weathering since then to degrade and destroy the craters [Schaber et al., 1992]. Venus has a fewer number of small craters than any other planet. Small projectiles vaporize or break up in the Venusian atmosphere before they reach the surface. Many craters display radar-bright or -dark halos, and a number of craters have extended deposits that are parabolically shaped and open to the west [Campbell et al., 1992]. A feature unique to Venusian craters is radar-bright outflow deposits that extend over great distances, following the local topography [Asimow and Wood, 1992].

Impact origin of craters is determined from a group of criteria. The features that best determine an impact origin for a crater are: (1) a circular rim crest outline; (2) flanks that gently rise above the surrounding terrain; (3) floors with elevations lower than those of the surrounding terrain; (4) an ejecta blanket surrounding the crater; and (5) an inner basin that might be present in very large craters. The Venusian impact crater Danilova is 48 kilometers (30 miles) in diameter. It has a central peak, a crater wall, a crater floor, an ejecta blanket, and crater outflow deposits. (See also the geological sketch map for the crater.)

The ejecta blanket and the circular rim of a crater are very bright in radar images because both are rough, with many facets oriented perpendicular to the radar illumination. Typically, the crater wall that slopes toward the radar appears compressed while the wall that slopes away from the radar appears expanded. Walls parallel to the illumination have intermediate brightness and widths.

The symmetry of a crater depends on the angle of impact of the projectile that formed it. Craters produced by an impact that is normal to the surface tend to be radially symmetric: rim crests have roughly equal elevations everywhere and are concentric with the crater floor outline, while flanks appear the same in all radial directions. However, most impact craters are produced by projectiles with trajectories that are oblique to the surface. When the angle is very oblique, the crater has a bilateral symmetry about the plane of the trajectory, with rim crests highest on the down-trajectory side and lowest on the up-trajectory side, while crater flanks extend to distances greater on the down-trajectory sides than on the up-trajectory sides.

Venusian impact craters have either a radar-bright or -dark crater floor, or both. The brightness of the crater floor in Magellan images appears to depend on the incidence angle of the radar, the size of the crater, the terrain on which the crater formed, and the amount of infilling by lava or impact melt.

中文知识：

金星是太阳系九大行星之一，按离太阳由近及远的次序排列为第二颗。它也是天空中最亮的星星。金星也是太阳系中唯一一颗没有磁场的行星。

概述

中国古人称金星为“太白”或“太白金星”，也称“启明”或“长庚”。古希腊人称为阿佛洛狄特，是希腊神话中爱与美的女神。而在罗马神话中爱与美的女神是维纳斯，因此金星也称做“维纳斯”。金星的天文符号用维纳斯的梳妆镜来表示。

hasesofvenus.jpg" target="_blank" >

hasesofvenus.jpg" target="_blank" >

金星的位相变化

金星同月球一样，也具有周期性的圆缺变化（位相变化），但是由于金星距离地球太远，用肉眼是无法看出来的。关于金星的位相变化，曾经被伽利略作为证明哥白尼的日心说的有力证据。

形状结构

金星的外表和地球非常相似。金星半径为6073千米，只比地球小300千米，体积是地球的0.88倍，质量是地球的4/5。因此被称为地球的姊妹星星。

金星的表面温度最高达447摄氏度。这是由于金星大气中二氧化碳的浓度在97%以上，使得金星上形成了很强的温室效应。这使得金星上昼夜温差很小，而且也造成金星大气压很高，大约为地球的90倍。

金星大气中存在一层又热又厚的硫酸雨滴和硫酸云雾。大气的主要成分是二氧化碳，占97％。而且金星的天空是橙黄色的。金星上也有雷电，曾经记录到的最大一次闪电持续了15分钟。

金星的公转是自东向西的，因此在金星上看到的太阳是西升东落的。金星一昼夜为243天，公转周期为225天。

地形地貌

金星的地貌非常复杂，60%是平原，另外还有高原、山地、裂谷。金星上最高的山是马克士威山，高达10590米。

一般认为，进行的地质构造曾经很活跃，很可能有还有活火山。另外，根据探测器的探测，发现金星的岩浆里含有水。

人类探索

在太空探测器探测金星以前，有的天文学家认为金星的化学和物理状况和地球类似，在金星上发现生命的可能性比火星还大。1950年代后期，天文学家用射电望远镜第一次观测了金星的表面。从1961年起，前苏联和美国向金星发射了30多个探测器，从近距离观测，到着陆探测。

大家可以在后面跟贴添加。

郁闷怎么这样。

大家点击一下查看。

Venus, the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover. Astronomers refer to Venus as Earth's sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula. However, during the last few years scientists have found that the kinship ends here. Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid droplets. At the surface, the atmospheric pressure is 92 times that of the Earth's at sea-level. Venus is scorched with a surface temperature of about 482° C (900° F). This high temperature is primarily due to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury. A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. To an observer on Venus, the Sun would rise in the west and set in the east. Until just recently, Venus' dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA's Pioneer Venus mission (1978), the Soviet Union's Venera 15 and 16 missions (1983-1984), and NASA's Magellan radar mapping mission (1990-1994). As these spacecraft began mapping the planet a new picture of Venus emerged. Venus' surface is relatively young geologically speaking. It appears to have been completely resurfaced 300 to 500 million years ago. Scientists debate how and why this occurred. The Venusian topography consists of vast plains covered by lava flows and mountain or highland regions deformed by geological activity. Maxwell Montes in Ishtar Terra is the highest peak on Venus. The Aphrodite Terra highlands extend almost half way around the equator. Magellan images of highland regions above 2.5 kilometers (1.5 miles) are unusually bright, characteristic of moist soil. However, liquid water does not exist on the surface and cannot account for the bright highlands. One theory suggests that the bright material might be composed of metallic compounds. Studies have shown the material might be iron pyrite (also know as "fools gold"). It is unstable on the plains but would be stable in the highlands. The material could also be some type of exotic material which would give the same results but at lower concentrations. Venus is scarred by numerous impact craters distrubuted randomly over its surface. Small craters less that 2 kilometers (1.2 miles) are almost non-existent due to the heavy Venusian atmosphere. The exception occurs when large meteorites shatter just before impact, creating crater clusters. Volcanoes and volcanic features are even more numerous. At least 85% of the Venusian surface is covered with volcanic rock. Hugh lava flows, extending for hundreds of kilometers, have flooded the lowlands creating vast plains. More than 100,000 small shield volcanoes dot the surface along with hundreds of large volcanos. Flows from volcanos have produced long sinuous channels extending for hundreds of kilometers, with one extending nearly 7,000 kilometers (4,300 miles). Giant calderas more than 100 kilometers (62 miles) in diameter are found on Venus. Terrestrial calderas are usually only several kilometers in diameter. Several features unique to Venus include coronae and arachnoids. Coronae are large circular to oval features, encircled with cliffs and are hundreds of kilometers across. They are thought to be the surface expression of mantle upwelling. Archnoids are circular to elongated features similar to coronae. They may have been caused by molten rock seeping into surface fractures and producing systems of radiating dikes and fractures金星上面的crater
General Characteristics
Impact craters are found to be distributed randomly but uniformly over the surface of Venus. Cratering of the terrestrial planets shows a record of two distinct periods, one from the late period of heavy bombardment and the other from a bombardment of asteroids and comets which occured more recently. Venus shows no record of the heavy bombardment period, indicating that it was resurface about 300 to 500 million years ago. The majority of Venusian craters appears pristine because they were formed after Venus was resurfaced; there has been very little geologic activity and weathering since then to degrade and destroy the craters [Schaber et al., 1992]. Venus has a fewer number of small craters than any other planet. Small projectiles vaporize or break up in the Venusian atmosphere before they reach the surface. Many craters display radar-bright or -dark halos, and a number of craters have extended deposits that are parabolically shaped and open to the west [Campbell et al., 1992]. A feature unique to Venusian craters is radar-bright outflow deposits that extend over great distances, following the local topography [Asimow and Wood, 1992]. Impact origin of craters is determined from a group of criteria. The features that best determine an impact origin for a crater are: (1) a circular rim crest outline; (2) flanks that gently rise above the surrounding terrain; (3) floors with elevations lower than those of the surrounding terrain; (4) an ejecta blanket surrounding the crater; and (5) an inner basin that might be present in very large craters. The Venusian impact crater Danilova is 48 kilometers (30 miles) in diameter. It has a central peak, a crater wall, a crater floor, an ejecta blanket, and crater outflow deposits. (See also the geological sketch map for the crater.) The ejecta blanket and the circular rim of a crater are very bright in radar images because both are rough, with many facets oriented perpendicular to the radar illumination. Typically, the crater wall that slopes toward the radar appears compressed while the wall that slopes away from the radar appears expanded. Walls parallel to the illumination have intermediate brightness and widths. The symmetry of a crater depends on the angle of impact of the projectile that formed it. Craters produced by an impact that is normal to the surface tend to be radially symmetric: rim crests have roughly equal elevations everywhere and are concentric with the crater floor outline, while flanks appear the same in all radial directions. However, most impact craters are produced by projectiles with trajectories that are oblique to the surface. When the angle is very oblique, the crater has a bilateral symmetry about the plane of the trajectory, with rim crests highest on the down-trajectory side and lowest on the up-trajectory side, while crater flanks extend to distances greater on the down-trajectory sides than on the up-trajectory sides. Venusian impact craters have either a radar-bright or -dark crater floor, or both. The brightness of the crater floor in Magellan images appears to depend on the incidence angle of the radar, the size of the crater, the terrain on which the crater formed, and the amount of infilling by lava or impact melt. 中文知识：金星是太阳系九大行星之一，按离太阳由近及远的次序排列为第二颗。它也是天空中最亮的星星。金星也是太阳系中唯一一颗没有磁场的行星。目录 [显示隐藏]  
1 概述
2 形状结构
3 地形地貌
4 人类探索
5 参看
[编辑]概述
中国古人称金星为“太白”或“太白金星”，也称“启明”或“长庚”。古希腊人称为阿佛洛狄特，是希腊神话中爱与美的女神。而在罗马神话中爱与美的女神是维纳斯，因此金星也称做“维纳斯”。金星的天文符号用维纳斯的梳妆镜来表示。

金星的位相变化
金星同月球一样，也具有周期性的圆缺变化（位相变化），但是由于金星距离地球太远，用肉眼是无法看出来的。关于金星的位相变化，曾经被伽利略作为证明哥白尼的日心说的有力证据。[编辑]形状结构
金星的外表和地球非常相似。金星半径为6073千米，只比地球小300千米，体积是地球的0.88倍，质量是地球的4/5。因此被称为地球的姊妹星星。金星的表面温度最高达447摄氏度。这是由于金星大气中二氧化碳的浓度在97%以上，使得金星上形成了很强的温室效应。这使得金星上昼夜温差很小，而且也造成金星大气压很高，大约为地球的90倍。金星大气中存在一层又热又厚的硫酸雨滴和硫酸云雾。大气的主要成分是二氧化碳，占97％。而且金星的天空是橙黄色的。金星上也有雷电，曾经记录到的最大一次闪电持续了15分钟。金星的公转是自东向西的，因此在金星上看到的太阳是西升东落的。金星一昼夜为243天，公转周期为225天。[编辑]地形地貌
金星的地貌非常复杂，60%是平原，另外还有高原、山地、裂谷。金星上最高的山是马克士威山，高达10590米。一般认为，进行的地质构造曾经很活跃，很可能有还有活火山。另外，根据探测器的探测，发现金星的岩浆里含有水。[编辑]人类探索
在太空探测器探测金星以前，有的天文学家认为金星的化学和物理状况和地球类似，在金星上发现生命的可能性比火星还大。1950年代后期，天文学家用射电望远镜第一次观测了金星的表面。从1961年起，前苏联和美国向金星发射了30多个探测器，从近距离观测，到着陆探测。

大家可以在后面跟贴添加。