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.
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. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, Jacobs/ESCG at NASA-JSC.
Noctilucent or “night shining” clouds form near the boundary of the mesosphere and thermosphere.
In June 2007, the Space Shuttle crew visiting the International Space Station (ISS) observed spectacular polar mesospheric clouds over north-central Asia. TThe red-to-dark region at the bottom of the image is the dense part of the Earth’s atmosphere.
Polar mesospheric clouds (also known as noctilucent, or “night-shining” clouds) are transient, upper atmospheric phenomena that are usually observed in the summer months at high latitudes (greater than 50 degrees) of both the Northern and Southern Hemispheres. They appear bright and cloudlike while in deep twilight. They are illuminated by sunlight when the lower layers of the atmosphere are in the darkness of Earth’s shadow.