Friday 4 March 2011

SDO Sundog Mystery

NASA's Solar Dynamics Observatory (SDO), best known for cutting-edge images of the sun, has made a discovery right here on Earth.

"It's a new form of ice halo," says atmospheric optics expert Les Cowley of England. "We saw it for the first time at the launch of SDO--and it is teaching us new things about how shock waves interact with clouds."

Ice halos are rings and arcs of light that appear in the sky when sunlight shines through ice crystals in the air. A familiar example is the sundog—a rainbow-colored splash often seen to the left or right of the morning sun. Sundogs are formed by plate-shaped ice crystals drifting down from the sky like leaves fluttering from trees.*

Last year, SDO destroyed a sundog—and that's how the new halo was discovered.

SDO lifted off from Cape Canaveral on Feb. 11, 2010—one year ago today. It was a beautiful morning with only a handful of wispy cirrus clouds crisscrossing the wintry-blue sky. As the countdown timer ticked to zero, a sundog formed over the launch pad. Play the movie, below, to see what happened next—and don't forget to turn up the volume to hear the reaction of the crowd:

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