Venus is the second planet in outward succession from the Sun, orbiting it at an average instance of 107.5 million kilometers (66.6 million miles) along a path that is very nearly circular. In size Venus is very much like the Earth. Its diameter is about 12,103 kilometers (7,520 miles), 0.95 times that of Earth; its density is 5.24 grams per cubic centimeter, as against Earth's 5.52; and its mass is 0.81 times that of our planet. But although in dimensions and probably in internal structure too, the Earth and Venus are sisters, Venus is in most other respects a world almost totally unlike our own.

Because Venus's path around the Sun lies within that of the Earth, the planet appears to us as a morning or evening star, rising just before or setting just after the Sun. In some parts of the world Venus may rise as much as three hours before dawn or set three hours after sunset. Venus is the most conspicuous of the planets and is in fact the brightest object in the night sky after the Moon.

As an inferior planet, that is, one whose orbit lies within that of the Earth, Venus shows shape changes, or phases, like the Moon and Mercury. When the Italian astronomer Galileo discovered this fact in the early 17th century, it provide convincing proof to the scientific world that the old Earth-centered idea of the Universe was wrong and that Copernicus's suggestion, that the Earth went around the Sun, was more likely to be correct.

Venus's dense atmosphere held back knowledge of the planet until the 20th century. Now the use of scientific techniques such as spectroscopy and radar has helped unravel some of the mysteries surrounding Venus.

Facts About Venus
Average Distance from the Sun: 107.5 million-km (66.6 miles)
Length of year: 224.7 Earth Days
Period of Axial Rotation: 243 Earth Days
Length of Venusian "Day": 118 Earth Days
Diameter: 12,103 km (7,520 miles)
Mass: 0.81 (Earth=1)
Density: 5.245 (water=1)
Average Surface Gravity: 0.904 (Earth=1)
Atmospheric Composition:
Carbon dioxide 96%; nitrogen 3.5%; water vapor 0.002%; traces of carbon monoxide, oxygen, sulfur dioxide, hydrochloric acid.

Upper cloud layers composed of sulfuric acid, sulfur dioxide, and free sulfur.
Atmospheric Pressure: 94 bars (Earth=1 bar)
Average Surface Temperature: 460C (860F)

1988 Encyclopaedia Britannica, Inc.

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