Polar mesospheric clouds—also known
as noctilucent or “night shining” clouds—form between 76 to 85
kilometers (47 to 53 miles) above the Earth’s surface, near the boundary
of the mesosphere and thermosphere, 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 and the ground is in darkness, these
high clouds may still be illuminated, lending them their ethereal,
“night shining” qualities.
Polar mesospheric clouds
have been observed from all human vantage points in both the Northern
and Southern Hemispheres—from the surface, in aircraft, and from the
International Space Station (ISS) —and tend to be most visible during
the late spring and early summer. Some atmospheric scientists seek to
understand their mechanisms of formation, while others have identified
them as potential indicators of atmospheric changes resulting from increases in greenhouse gas concentrations.
This astronaut photograph was taken when the ISS was over the Pacific Ocean south of French Polynesia. While most polar mesospheric cloud
images are taken from the ISS with relatively short focal length lenses
(to maximize the field of view), this image was taken with a long lens
(400 mm) allowing for additional detail of the cloud forms. Below the
brightly-lit noctilucent clouds, across the center of the image, the
pale orange band is the stratosphere.
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Other images of polar mesospheric clouds:
- Polar Mesospheric Clouds, Northern Hemisphere
- Polar Mesospheric Clouds Illuminated by Orbital Sunrise
- Polar Mesospheric Clouds, Southern Hemisphere
- Polar Mesospheric Clouds Over Central Asia
Astronaut photograph ISS034-E-24622
was acquired on January 5, 2013, with a Nikon D3S digital camera using a
400 millimeter lens, and is provided by the ISS Crew Earth Observations
experiment and Image Science & Analysis Laboratory, Johnson Space
Center. The image was taken by the Expedition 34 crew.
- Instrument: ISS - Digital Camera
