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Explanation: What's happening above those clouds? In the past few years, videos have appeared on the web detailing an unusual but little known phenomenon: rapid light changes over clouds. Upon inspection and contemplation, a leading hypothesis for its cause has now emerged. In sum, this hypothesis holds that a lightning discharge in a thundercloud can temporarily change the electric field above the cloud where charged ice crystals were reflecting sunlight. The new electric field quickly re-orients the geometric crystals to a new orientation that reflects sunlight differently. In other words, a lightning discharge can cause a sundog to jump. Soon,...

On March 20th, Danish photographer Jesper Gronne looked up at the clouds and saw not just one or two but three concentric halos around the sun. Before the rare display could fade, he grabbed his camera (a Canon 5D) and snapped more than 20 pictures. Stacking the images on his computer yielded a pin-up quality record of the event: I never expected to see such a rich variety of ice halos here in lowland Denmark--and it's not even winter anymore!" he marveled. What could cause such an apparition? Atmospheric optics expert Les Cowley explains: "We can work outwards from the...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 December 30 A Sun Pillar Credit & Copyright: Dave Liquorice Explanation: Have you ever seen a sun pillar? When the air is cold and the Sun is rising or setting, falling ice crystals can reflect sunlight and create an unusual column of light. Ice sometimes forms flat, stop-sign shaped crystals as it falls from high-level clouds. Air resistance causes these crystals to lie nearly flat much of...