Image: Polar Mesospheric Clouds over the South Pacific Ocean


Polar mesospheric clouds--also known as noctilucent, or "night shining" clouds--are formed 76 to 85 kilometers above Earth's surface near the mesosphere-thermosphere boundary of the atmosphere, a region known as the mesopause. At these altitudes, water vapor can freeze into clouds of ice crystals. When the sun is below the horizon such that the ground is in darkness, these high clouds may still be illuminated--lending them their ethereal, "night shining" qualities. Noctilucent clouds have been observed from all human vantage points in both the Northern and Southern Hemispheres -- from the surface, in aircraft, and in orbit from the space station--and tend to be most visible during the late spring and early summer seasons.


ISS034-E-024622 (5 Jan. 2013) - high res (0.5 M) low res (37 K)

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