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."
For a brief instant, the planet had turned into a "ring of fire."