Venus is the second planet from the sun. It is a terrestrial planet, and has an atmosphere consisting mainly of carbon dioxide and a small amount of nitrogen with a pressure at the surface about 90 times that of Earth. This results in a strong greenhouse effect, causing temperatures at the surface to reach 500° C. Due to the thermal inertia and convection of its dense atmosphere, surface temperature does not vary significantly between the night and day sides of Venus despite its extremely slow rotation.
Because its orbit takes it between the Earth and the Sun, Venus seen from Earth exhibits visible phases in much the same manner as the Earth's moon. Galileo Galilei was the first to observe the phases of Venus. This observation supported Copernicus' heliocentric description of the solar system.
Venus has slow retrograde rotation, meaning it rotates from east to west instead of west to east as all other known planets in the solar system do. It is not known for sure why Venus is different in this manner, although it may be the result of a collision with a large asteroid at some time in the past.
Transits of Venus, when the planet crosses directly between the Earth and the Sun' visible disc, are important astronomical events. The previous set of transits of Venus occurred within the interval of 1874-1882, and the next set of transits will not occur until the period of 2004-2012.
The first successful Venus probe was the American Mariner 2 probe, which flew past Venus in 1962. It established that Venus has no magnetic field and confirmed the planet's rotation rate. The American space program followed up the Mariner program with a series of Pioneer orbiters and finally the recent Magellan orbiter, mapping the surface of Venus by using radar to penetrate its permanent total cloud cover. The Soviet Union sent a number of landers, with Venera 9 and 10 each returning a single black and white photograph of Venus' surface in 1975 and Venera 13 and 14 returning a number of colour photographs from Venus' surface in 1982. In 1985 the Soviet Vega 1 and 2 probes each deployed a sensor-laden balloon in Venus' atmosphere in addition to placing landers on the surface. No lander survived for more than about an hour before failing under Venus' intense surface heat and pressure.
Venus has two major continent-like plateaus on its surface, rising over vast plains. The northern plateau is named Ishtar Terra and has Venus' highest mountains on it, the Maxwell Montes. In the southern hemisphere is the larger Aphrodite Terra. Venus' surface appears to consist largely of recently solidified basalt, with very few meteor craters. This suggests that Venus underwent a major resurfacing event recently. It is theorized that Venus does not have mobile plate tectonics like Earth does, but instead undergoes massive volcanic upwellings at regular intervals that inundate its surface with fresh lava.
- Mass: 0.814 earth masses
- Radius: 6052 km
- Length of year: 224.7 earth days
- Rotation period: 243 earth days (retrograde)
- Mean surface temperature: 456.85 C (854.33°F)
- Surface area: 460 million km2
- Mean distance from sun: 108,208,930 km / 0.723 AU
- Surface gravity: 0.903 times earth surface gravity
See also: Venus the goddess