On Jan. 25th, cold air from Canada descended over Ohio, producing scattered snow showers and some very unusual clouds. "My wife thought this cloud looked like an alien spacecraft," says photographer Ed Kreminski, "but my kids thought it looked like a blimp on it's way to cover a sporting event."

Photo details: Olympus E-1, 50-200mm lens, ISO 100
full size

A better analogy, says atmospheric optics expert Les Cowley, might be "an oily pool in the sky."

"The colors of oil films on puddles appear when light reflected from the top and bottom of the film merges together," he explains. "Light waves interfere, strengthening some colors and weakening others."

The same thing is happening in this iridescent cloud--except instead of oil, we have tiny water droplets. "The cloud is thin and it contains many droplets of about the same size." This combination produces an interference effect akin to an oil slick--without the greasy residue.

http://www.spaceweather.com/