Venus is a dim world of intense heat and volcanic activity. Similar in structure and size to Earth, Venus' thick, toxic atmosphere traps heat in a runaway 'greenhouse effect.' The scorched world has temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains. Venus spins slowly in the opposite direction of most planets.
Distance from the sun: About 67 million miles, about 3/4 as far as the Earth is from the sun.
Year: About 225 Earth days.
Day: About 243 Earth days.
Average diameter: About 7,500 miles, almost as large as Earth.
Surface temperature: 864 degress Fahrenheit.
Atmosphere: Carbon dioxide, nitrogen.
When Venus transits the sun on June 5th and 6th, an armada of spacecraft and ground-based telescopes will be on the lookout for something elusive and, until recently, unexpected: The Arc of Venus.
"I was flabbergasted when I first saw it during the 2004 transit," recalls astronomy professor Jay Pasachoff of Williams College. "A bright, glowing rim appeared around the edge of Venus soon after it began to move into the sun."
One of the biggest mysteries of Venus is super-rotation. The whole atmosphere circles the planet in just four Earth days, much faster than the planet's spin period of 243 days. "The dynamics of super-rotation are still a puzzle despite a wealth of data from landmark missions such as NASA's Pioneer Venus, Russia's Venera and VEGA missions, NASA's Magellan and more recently ESA's Venus Express."
Transits of Venus are so rare that they only happen twice in a lifetime. About every 115 years, Venus will appear to cross over the face of our home star twice, with eight years passing between the pair of transits. This stunning phenomenon is not only incredible to watch, but it provides a unique opportunity for scientific observations of one of our nearest neighboring planets.
Just as on Earth, each of the layers of Venus’ atmosphere absorb light differently from one another. Some layers may completely absorb a certain wavelength of light, while that same wavelength can pass right through another layer. As Venus passes across the face of the sun -- which emits light in almost every wavelength of the electromagnetic spectrum -- scientists get a rare chance to see how all different types of light filter through Venus’s atmosphere.