Venus

Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better. Venus's apparition as the morning star is also sometimes called Lucifer. Since Venus is 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's heliocentric theory of the solar system. The first spacecraft to visit Venus was Mariner It was subsequently visited by many others more than in all so far, including Pioneer Venus and the Soviet Venera the first spacecraft to land on another planet, and Venera which returned the first photographs of the surface. The first orbiter, the US spacecraft Magellan.

produced detailed maps of Venus surface using radar. ESA's Venus Express is now in orbit with a large variety of instruments. Venus rotation is somewhat unusual in that it is both very slow Earth days per Venus day, slightly longer than Venus' year and retrograde. In addition, the periods of Venus rotation and of its orbit are synchronized. such that it always presents the same face toward Earth when the two planets are at their closest approach.

Whether this is a resonance effect or merely a coincidence is not known. Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar: 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 very 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. It may be the least hospitable place for life in the solar system.