Portal:Solar System/Selected article/4 Source: en.wikipedia.org/wiki/Portal:Solar_System/Selected_article/4
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" among the planets of the Solar System for its orbit being the closest to Earth's, both being rocky planets and having the most similar and nearly equal size and mass. Venus, though, differs significantly by having no liquid water, and its atmosphere is far thicker and denser than that of any other rocky body in the Solar System. It is composed of mostly carbon dioxide and has a cloud layer of sulfuric acid that spans the whole planet. At the mean surface level, the atmosphere reaches a temperature of 737 K (464 °C; 867 °F) and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the atmosphere into a supercritical fluid.
Venus is the third brightest object in Earth's sky, after the Moon and the Sun. As an inferior planet, Venus always appears from Earth relatively close to the Sun than Earth, alternating between being the brightest "morning star" or "evening star".
The orbits of Venus and Earth make the two planets approach each other in synodic periods of 1.6 years. In the course of this, Venus comes closer to Earth than any other planet, while on average Mercury stays closer to Earth and any other planet due to its more inferior orbit. For interplanetary spaceflights, Venus is frequently used as a waypoint for gravity assists because it offers a more economical and faster route. Venus has no moons and has a very slow retrograde rotation about its axis, a result of competing forces of solar tidal locking and differential heating of Venus's massive atmosphere. As a result a Venusian day is 116.75 Earth days long, about half a Venusian solar year, which is 224.7 Earth days long. (Full article...)