Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet, being orbital neighbours as well as Venus having the most similar mass and size to Earth among the planets of the Solar System. While both are rocky planets, Venus has an atmosphere much thicker and denser than Earth and any other rocky body in the Solar System. Its atmosphere is composed of mostly carbon dioxide, with a global sulfuric acid cloud cover and no liquid water. At the mean surface level the atmosphere reaches a temperature of 737 K and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the carbon dioxide atmosphere into a supercritical fluid.
Venus is the third brightest object in Earth's sky, after the Moon and the Sun, and, like Mercury, always appears relatively close to the Sun, either as a "
morning star" or an "
evening star", resulting from orbiting closer (inferior) to the Sun than Earth.