Venus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named most likely because it is the brightest of the planets recognized to the ancients. 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 commonly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the sunset star, but the Greek astronomers knew better.
Venus' rotary motion is somewhat unusual in that it is both very slow (243 Earth days per Venus day, somewhat longer than Venus' year) and retrograde. Additionally, the periods of Venus' rotary motion and of its orbit are synchronized such that it for all time presents the same face in the direction of Earth when the two planets are at their neighboring approach. Whether this is a resonance effect or just a coincidence is not known.
Venus is at times regarded as Earth's sister planet. In some ways they are especially similar:
* Venus is only somewhat smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).
* Both have a small number of craters indicating relatively young surfaces.
* Their densities and chemical compositions are alike.
Because of these similarities, it was considered that below its dense clouds Venus might be very earthlike and might even have life. However, unfortunately, more detailed study of Venus reveals that in lots of important ways it is radically different from Earth. It may be the slightest hospitable place for life in the solar system.
The force of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a deepness of 1 km in Earth's oceans). It is composed generally of carbon dioxide. There are numerous layers of clouds many kilometers thick composed of sulfuric acid. These clouds entirely obscure our view of the surface. This dense atmosphere creates a run-away greenhouse effect that raises Venus' face temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is truly hotter than Mercury's in spite of being nearly twice as far from the Sun. The oldest terrains on Venus appear to be about 800 million years old. Extensive volcanism at that time wiped out the in advance surface counting any large craters from early in Venus' history.