Noctilucent clouds, credit Dr. Joseph Shaw

This is a photograph of noctilucent ("night-shining") clouds observed in the sky northeast of Bozeman, Montana (45.6 N, 111 W) at 4:40am on 16 July 2009 when the sun was still more than 10 degrees below the horizon. This is a rare mid-latitude photograph of ultra-high-level clouds that form at 80-85 km, primarily at high latitudes. These "night-shining" clouds are so high that they are illuminated by direct sunlight when the underlying atmosphere is still in total darkness. Photo copyright Joseph A. Shaw (Nikon D300, ISO 400, Nikkor 20-mm lens at f/2.8 for 1/2 s).

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