Venus us the second planet from the Sun and the sixth largest. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%.

Venus (Greek: Aphrodite, Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named probably because it is brightest of the planets known to the ancients. (With a few exceptions, the surface features on Venus are named for figures.)

Venus has been known since prehistoric times. IT is the brightest object in the sky for the Sun and the Moon. Like Mercury, it was probably thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better.

Since Venus us an inferior planet, it shows phases when viewed with a telescope from the perspective of Earth. Galileo's observation of this phenomenon was important evidence in favor of Copernicus' heliocentric theory of the solar system.

The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on surface. Most recently, the orbiting US spacecraft Magellan produced detail maps of Venus' surface using radar (above).

Venus' rotation is somewhat unusual in that it is both very slow (243 Earth days per Venus day, slightly longer than Venus' year) and retrogrades. In addition, the periods of Venus' rotation and of its orbit are synchronized such that it is always present the same face toward Earth when the two planet are at their closest approach. Whether this is a resonance effect or merely coincidence is not known.

• Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar:
• Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).
• Both have few craters indicating relatively young surfaces.

Their densities and chemical compositions are similar.

Because of these similarities, it was thought that below its dense clouds Venus might be Earthlike and might even have life. But, unfortunately, more detailed study of Venus reveals that in many important ways it is radically different from Earth.

Venus probably once had a large amount of water like Earth but it all boiled away. Venus is now quite dry. Earth would have suffered the same fate had it been just a little closer to the Sun. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.

Most of Venus' surface consist of gently rolling plains with little relief. There are also several broad depressions: Atalanta Planitia, Guinevere Planitia, and Luvinia Planitia. There are two large highland areas: Ishtar Terra in the Northern Hemisphere (about the size of Australia) and Aphrodite Terra along the equator (about the size of South America). The interior of Ishtar consists mainly of a high plateau, Lakshmi Planum, which is surrounded by the highest mountains on Venus including the enormous Maxwell Montes.

There are no small craters on Venus. It seems that small meteoroids burned up in Venus' dense atmosphere before reaching the surface. Craters on Venus seem to come in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.

The oldest terrain on Venus seem to be about 800 million years old. Extensive volcanism at that time wiped out the earlier surface including any large craters from early in Venus' history.

The interior of Venus is probably very similar to that Earth: an iron core about 3000km in radius, a molten rocky mantle comprising the majority of the planet. Recent results from the Magellan gravity data indicate that Venus' crust is stronger and thicker than had previously been assumed. Like Earth, convention in the mantle produces stress on the surface, which is relieved in many relatively small regions instead of being concentrated at plate boundaries, as is the case on Earth.

Venus has no magnetic field, perhaps because of its slow rotation. It has no satellites and thereby hangs a tale. Venus is usually visible with the naked eye. Sometimes (inaccurately) referred to as the morning star or the evening star, it is by far the brightest "star" in the sky.

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