This astronaut photograph of polar mesospheric clouds was acquired at an altitude of just over 200 miles (about 321 kilometers) in the pre-dawn hours (18:24:01 Greenwich Mean Time) on July 22, 2008, as the International Space Station was passing over western Mongolia in central Asia. The dark horizon of the Earth appears at the bottom of the image, with some layers of the lower atmosphere already illuminated by the rising Sun. The higher, bluish-colored clouds look much like wispy cirrus clouds, which can be found as high as 60,000 feet (18 kilometers) in the atmosphere. However noctilucent clouds, as seen here, are observed in the mesosphere at altitudes of 250,000 to 280,000 feet (about 76 to 85 kilometers).
Astronaut observations of polar mesospheric clouds over northern Asia in June and July are not uncommon. The crew of the International Space Station acquired this image and many others in support of research for the International Polar Year. Some researchers link increased observations of these clouds to changes in global climate.