Station Crew Sees 'Night-Shining' Clouds
In
both the Earth's Northern and Southern Hemispheres polar mesospheric
clouds are at the peak of their visibility, during their respective late
spring and early summer seasons. Visible from aircraft in flight, the
International Space Station and from the ground at twilight, the clouds
typically appear as delicate, shining threads against the darkness of
space--hence their other names of noctilucent or "night-shining" clouds.
On June 13, 2012, when this image was taken from the space station as
it passed over the Tibetan Plateau, polar mesospheric clouds were also
visible to aircraft flying over Canada. In addition to the still image
above, the station crew took a time-lapse image sequence of polar
mesospheric clouds several days earlier on June 5, while passing over
western Asia. It is first such sequence of images of the phenomena taken
from orbit.
Polar mesospheric clouds form between 47 to 53
miles (76 to 85 kilometers) above Earth’s surface when there is
sufficient water vapor at these high altitudes to freeze into ice
crystals. The clouds are illuminated by the sun when it is just below
the visible horizon, lending them their night-shining properties. In
addition to the polar mesospheric clouds trending across the center of
the image, lower layers of the atmosphere are also illuminated. The
lowest layer of the atmosphere visible in this image--the
stratosphere--is indicated by dim orange and red tones near the horizon.
Image Credit: NASA
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