The elegant white planet orbiting the Sun is called Venus after the Roman goddess of beauty. Although similar to the Earth in size(7,500miles) - compared to Earth's diameter(7,900miles) and mass (Venus a bit more than four-fifths the mass of Earth), the Venusian surface and atmosphere are far different from ours.
Like Mercury, Venus is at times an evening star and at other times a morning star, depending on whether it is to the east or west of the Sun as viewed from the Earth. The planet may rise as much as four hours before the Sun, and may sets as much as four hours after it.
Venus revolves around the Sun once every 225 days in an orbit that is very nearly circular. And as it revolves, it is quite far indeed. But at its closest, when it is between the Sun and Earth, it is only some 26million miles away.
Venus like Mercury, shows a complete of phases, or shapes, to an observer on Earth armed with a small telescope or good binoculars. When the planet is at the farthest part of its orbit from the Earth, it appears as a disk. When Venus is between the Sun and the Earth, it is seldom visible. About 35days before and after this time, it appears as a crescent and is at its brightest - two and on-half times brighter than when it is sees as disk.
BENEATH THE GODDESS VEIL
The surface of Venus is obscured by the planet's thick clouds, and so is invisible to optical instruments. For centuries, astronomers could only guess what lay beneath this veil. Some conjured tales of swamps, forests, and strange creatures.
Starting in 1962 the United States and the Soviet Union sent more than 20 probes to the planet for a true view. The U.S pioneer-Venus 1 craft and soviet Venera 15 and 16 orbiters used radar to pierce the thick clouds and make low-resolution maps of the planet's surface. The mapping revealed mainly rolling upland plains, some lowland plains, and two highland areas. One called Aphrodite Terra, is about half the size of Africa. The other highland, Ishtar Terra, is about the size of the United States, and contains named Maxwell Montes.
Other Venera probes actually traveled through the clouds, landed softly on the surface, and transmitted the first color pictures of the planet's surface. Venusian crust showed that it contained basaltic rock similar to that associated on Earth with recent volcanic activity.
The U.S spacecraft Magellan launched in May 1989, has radar-mapped most of the Venusian surface with far better resolution than previous craft. Magellan cracks and fissures, rugged mountains, and bizarre "pancake domes" formed by hot lava welling up from beneath the surface.
Magellan also photographed giant craters formed when large hunks of rock from space crashed into the planet. Interestingly, Even the smallest craters found in Venus are quite huge-over 2.5 miles in diameter. Only very large hunks of space rock can survive the fiery passage through Venus' thick atmosphere and reach surface. Perhaps the biggest surprise from Magellan's pictures is the apparent lack of erosion on Venus. The mountains, craters, and other surface features appear rough and unweathered, almost as if they were newly formed. A major reason for this is that Venus is bone-dry. Water on Earth smooths down the surfaces features. Rivers, for example, gradually change mountains into valleys. But with surface temperatures of 896F (480C), Venus is too hot for water. If Venus did have water init past, it must have quickly evaporated.
Though there appear to be no signs that water ever flowed across Vebus' surface, Magellan's pictures show long channels cut by of hot lava. Volcanoes must have resurfaced Venus in its recent past, because the planet has far fewer craters than do Mars or the Moon. Scientists suspect that Venus volcanic face-lift came within the past few hundred million years.
Scientist are also trying to understand the geologic forces responsible for producing the volcanoes, mountain belts, and other surface features of Venus. On Earth the crust is divided into separate moving plates. Their movement, a process known as plate tectonics, is responsible for mountain building, seafloor spreading, and earthquakes. The crust of Venus does not appear to work in this way. Instead, up-wellings of hot, light material and down-wellings of cooler, dense material may pull and shove the surface crust.
BENEATH THE GODDESS VEIL
The surface of Venus is obscured by the planet's thick clouds, and so is invisible to optical instruments. For centuries, astronomers could only guess what lay beneath this veil. Some conjured tales of swamps, forests, and strange creatures.
Starting in 1962 the United States and the Soviet Union sent more than 20 probes to the planet for a true view. The U.S pioneer-Venus 1 craft and soviet Venera 15 and 16 orbiters used radar to pierce the thick clouds and make low-resolution maps of the planet's surface. The mapping revealed mainly rolling upland plains, some lowland plains, and two highland areas. One called Aphrodite Terra, is about half the size of Africa. The other highland, Ishtar Terra, is about the size of the United States, and contains named Maxwell Montes.
Other Venera probes actually traveled through the clouds, landed softly on the surface, and transmitted the first color pictures of the planet's surface. Venusian crust showed that it contained basaltic rock similar to that associated on Earth with recent volcanic activity.
The U.S spacecraft Magellan launched in May 1989, has radar-mapped most of the Venusian surface with far better resolution than previous craft. Magellan cracks and fissures, rugged mountains, and bizarre "pancake domes" formed by hot lava welling up from beneath the surface.
Magellan also photographed giant craters formed when large hunks of rock from space crashed into the planet. Interestingly, Even the smallest craters found in Venus are quite huge-over 2.5 miles in diameter. Only very large hunks of space rock can survive the fiery passage through Venus' thick atmosphere and reach surface. Perhaps the biggest surprise from Magellan's pictures is the apparent lack of erosion on Venus. The mountains, craters, and other surface features appear rough and unweathered, almost as if they were newly formed. A major reason for this is that Venus is bone-dry. Water on Earth smooths down the surfaces features. Rivers, for example, gradually change mountains into valleys. But with surface temperatures of 896F (480C), Venus is too hot for water. If Venus did have water init past, it must have quickly evaporated.
Though there appear to be no signs that water ever flowed across Vebus' surface, Magellan's pictures show long channels cut by of hot lava. Volcanoes must have resurfaced Venus in its recent past, because the planet has far fewer craters than do Mars or the Moon. Scientists suspect that Venus volcanic face-lift came within the past few hundred million years.
Scientist are also trying to understand the geologic forces responsible for producing the volcanoes, mountain belts, and other surface features of Venus. On Earth the crust is divided into separate moving plates. Their movement, a process known as plate tectonics, is responsible for mountain building, seafloor spreading, and earthquakes. The crust of Venus does not appear to work in this way. Instead, up-wellings of hot, light material and down-wellings of cooler, dense material may pull and shove the surface crust.
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