Mysterious night-shining clouds getting brighter

The night, increasingly, is aglow with the luminescence of polar mesospheric, or noctilucent, clouds. Space.com examines this phenomenon:

Clouds bright enough to see at night are not as hard to find as they once were.

These so-called night-shining clouds are still rare -- rare enough that Matthew DeLand, who has been studying them for 11 years, has seen them only once. But his odds are increasing. [Related: In Images: Reading the Clouds.]

These mysterious clouds form between 50 and 53 miles (80 and 85 kilometers) up in the atmosphere, altitudes so high that they reflect light long after the sun has dropped below the horizon.

DeLand, an atmospheric scientist with NASA's Goddard Space Flight Center in Greenbelt, Md., has found that night-shining clouds -- technically known as polar mesospheric or noctilucent clouds -- are forming more frequently and becoming brighter. He has been observing the clouds in data from instruments that have been flown on satellites since 1978.

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