The transit of Venus across the face of the sun Tuesday offered astronomers a chance to examine the dense atmosphere of Earth's 'sister planet.'
Cape Canaveral, Fla.
The planet Venus made a slow transit across the face of the sun on Tuesday, the last such passing that will be visible from Earth for 105 years.
Transits of Venus happen in pairs, eight years apart, with more than a century between cycles. During Tuesday's pass, Venus took the form of a small black dot slowly shifting across the northern hemisphere of the sun.
Armchair astronomers watched the six-hour and 40-minute transit on the Internet, with dozens of websites offering live video from around the world.
Closeup views from the Prescott Observatory in Arizona, fed into Slooh.com's webcast, showed a small solar flaring in the making just beneath Venus' sphere.
Tuesday's transit, completing a 2004-2012 pair, began at 6:09 p.m. EDT (2209 GMT).
"I've been planning this for a while," space station flight engineer Don Pettit said in a NASA interview. "I knew the transit of Venus would occur during my rotation, so I brought a solar filter with me."
It's not all about pretty pictures. Several science experiments were planned, including studies that could help in the search for habitable planets beyond Earth.
Telescopes, such as NASA's Kepler space telescope, are being used to find so-called extrasolar planets that pass in front of their parent stars, much like Venus passing by the sun.