The second planet from the Sun, attaining the greatest brilliancy in the night sky, outshining all the stars, hence its poetic names 'morning / evening star'. It has no natural satellite. It has the following characteristics: mass 4.87 � 10²⁴ kg; radius 6051 km / 3760 mi; mean density 5.2 g / cm³; equatorial gravity 860 cm / s²; rotational period 243 days (retrograde); orbital period 224.7 days; obliquity 0�; orbital eccentricity 0.007; mean distance from the Sun 108.2 � 10⁶ km / 67.2 � 10⁶ mi.

Venus and Earth are almost the same size. Venus is the closest planet to Earth, but it does not have oceans or human life like Earth. It approaches nearer to the Earth than any other planet, and is a near twin to Earth in size and density, but with a radically different atmosphere of mainly carbon dioxide, 90 times denser than our own, and with surface temperatures near 460�C. This planet is unusual because it rotates in a direction opposite that of all of the other planets. Venus spins very slowly as it orbits the Sun. There is no observable magnetic field.

Atmosphere

Venus has very thick, rapidly spinning clouds of sulfur dioxide and sulphuric acid droplets which cover the planet completely, obscuring any surface details. There are constant thunderstorms in these clouds. The thick atmosphere and cloud cover create a greenhouse effect that maintains high temperatures, even though clouds reflect a large fraction of incident sunlight, so Venus appears very bright to us here on Earth.

Pressure from the dense atmosphere is about 90 times greater than Earth's and would crush a human. This is a very unpleasant place, with winds that blow constantly at hundreds of miles per hour and extremely high temperatures. This planet is an example of a runaway greenhouse effect. Venus gets so hot during the day that it could melt a lead cannonball. The temperature rises to 484 degrees Celsius on the side facing the Sun.

Surface

The surface of Venus has many craters which were made by meteorites and asteroids crashing into the planet. Venus also has volcanoes.

The surface was mapped at sub-kilometre resolution by the Magellan spacecraft in 1990-2. About 85% consists of volcanic plains (mostly at low elevations) marked by thousands of individual volcanic constructs and (unlike most other solid planetary surfaces) relatively few (c.900) impact craters. The most extensive plains are flood lavas, within which are found shield volcanoes, cones, and domes of up to c.90 km / 60 mi diameter.

Some features appear unique to Venus, and have been given descriptive names: coronae are complex volcano-tectonic features whose morphology suggests they result from mantle plumes; arachnoids have inner concentric and outer radial ridges and fractures; pancake domes are almost perfectly circular, with steep sides and heights of a few hundred metres. The surface is evidently very young (200-700 million years).

Surface features are disrupted by tectonic activity, and deformation occurs over a wide variety of styles and scales (up to 1000 km / 600 mi). There is no evidence for Earth-like plate tectonics, though some features do resemble terrestrial subduction trenches. Reconstruction of the planetary history by interpretation of the Magellan geological observations and the earlier Pioneer and Venera atmospheric composition measurements is a process expected to continue for many years.

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Venus is the second planet from the Sun, named after the Roman goddess Venus (mythology). It is a terrestrial planet, very similar in size and bulk composition to Earth; it is sometimes called Earth's "sister planet" as a result of this similarity.

Because Venus is closer to the Sun than Earth is, it is always in roughly the same direction as the Sun, so on Earth it can only be seen just before sunrise or just after sunset. It is sometimes referred to as the "morning star" or the "evening star", and when it appears it is by far the brightest point of light in the sky.

Transits of Venus, when the planet crosses directly between the Earth and the Sun's visible disc, are rare astronomical events. The first time such a transit was observed was on December 4, 1639 by Jeremiah Horrocks and William Crabtree. A transit in 1761 observed by Mikhail Lomonosov provided the first evidence that Venus had an atmosphere, and the 19th century observations of parallax during its transits allowed the distance between the Earth and Sun to be accurately calculated for the first time. The previous set of transits of Venus occurred within the interval of 1874 - 1882, and the next set of transits will occur in the period of 2004 - 2012.