The second planet from the Sun. It has a dense atmosphere of 96% carbon dioxide, 3.5% nitrogen, and 0.5% water vapor, H₂SO₄ (sulfuric acid), HCl (hydrochloric acid), and HF (hydrofluoric acid). Venusian clouds are arranged in three bands, the highest of which extends to 68 km above the planet's surface. Thunder and lightning storms are common, and the surface pressure is 90 atm. Because of the greenhouse effect, the surface temperature is 745 K. The Venusian zonal (east-west) wind blows at 100 m s^-1, for a period of only four days at the equator! They were first detected by tracking chevron-shaped markings seen in the UV, which may be due to Cl₂, amorphous sulfur, or SO₂. The meridional wind (north-south) is much less.

Venus spins retrograde with a sidereal period of 243.01 days. It has an orbital period of 225 days, so its solar period (Venus day) is 117 earth days. The sidereal rotation period is very close to a resonance with Earth at 243.16 days, but the earth should have no business exerting an significant torques on Venus. Retrograde rotation may be an accident of birth, although it is possible that atmospheric tides produce a retrograde torque.

Venus's center of figure is offset 0.34 km from its center of mass, but this offset is much smaller than that of the moon, Mars, or Earth. There is a high correlation between gravity and elevation, so topography might appear to be supported by a strong lithosphere. Venus's high surface temperature, however, makes this unlikely. Instead, it is possible that convection creates upwellings which deform the surface. Geophysical modeling involving an examination of the eclogite stability field indicates that a surface layer of 100-170 km should be present.

Venus has a number of inactive shield volcanos, but the number of identifiable craters is far below the expected value. The highest plateau is Ishtar Terra, upon which rests Maxwell, Venus's highest mountain. Alpha Regio in the Southern hemisphere is characterized by its parallel ridges. Venus's mantle and crust are thought to be composed of silicates and it core is thought to be nickel-iron. The Magellan radar mapper arrived at Venus in 1990, and the images it is returning will likely fundamentally change our understanding of the planet. Venus has no magnetic field and no moon, and the plasma regions surrounding Venus do not contain radiation belts like the Earth's van Allen radiation belts.

Four transits of Venus (i.e., Venus passes between the Sun and Earth) occur every 243 years. Transits occur around June 6 or December 7 in the following years (where * indicates a December transit):

The transits repeats every 243 years after 4 transits at intervals of 105.5, 8, 121.5 and 8 years. 152 Venus synodic orbits are roughly equal to 243 solar years, and 5 Venus synodic orbits are roughly equal to 8 solar years plus 0.83 days. Transits of Venus can last up to 6 hours.

Schröter Effect