Friday, June 8, 2012

The Mystery of the Arc of Venus

"We do not understand why our sister planet's atmosphere evolved to be so different than Earth's." -- Thomas Widemann, Observatoire de Paris

[On June 5, 2012, Venus passed directly between the Earth and the Sun, a rare astronomical phenomenon known as the "Transit of Venus" that will occur again in 105 years. This month, 13.7 Billion Years considers "Earth's twin," from the scientific study of the planet to its mythological underpinnings, with the series Second Rock from the Sun.]

Earlier this week, while most of us were content simply to witness Venus move slowly in front of the massive solar disk, there were several astronomers who were looking for something in particular: the mysterious "arc of Venus."

During the last transit, in 2004, astronomers were surprised by the strange phenomenon, what has been described as a "ring of fire"' around the planet as it moved between the Sun and Earth.

"I was flabbergasted when I first saw it during the 2004 transit," said 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."

After doing some research following the event, astronomers figured out what happened: Venus's atmosphere was refracting sunlight that passed though the layers of air above its clouds, producing the strange glowing arc of light.

Unlike the last Transit of Venus, astronomers were prepared for the mysterious arc this time around, and optimized their recordings of the event to capture the ring of fire for deeper analysis.

What they find, they hope, will help to shed light not only on how Venus was formed, but how Earth was too.

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image: Three photos from the Arc of Venus observed during the planet's 2004 transit by amateur astronomer near Toulouse, France. (credit: André Rondi)

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