often appear at high latitudes in corresponding summer months. Also known as polar mesospheric clouds, they form as water vapor is driven into the cold upper atmosphere. Fine dust supplied by disintegrating meteors or volcanic ash provides sites where water vapor can condense, turning to ice at the cold temperatures in the mesosphere. Poised at the edge of space some 80 kilometers above, these icy clouds really do reflect sunlight toward the ground. They are visible here even though the Sun itself was below the horizon, as seen on July 16 from Sweden's Färnebofjärdens National Park.
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& Michigan Tech. U.
Based on Astronomy Picture Of the Day
Publications with keywords: noctilucent clouds
Publications with words: noctilucent clouds