June 26, 2012 -- High-altitude clouds were spotted over western Asia by the crew of the International Space Station on June 13 during one of their 16 orbits of the planet that day... the photo above shows the wispy filaments shining brightly in the mesosphere above western Iraq and Uzbekistan.
Called noctilucent "night-shining" clouds, these upper atmospheric features are more common during late spring and early summer in the northern hemisphere. They can be seen from the ground as bright strands, waves or webs against the night sky, visible long after the sun has set.
Also known as polar mesospheric clouds, the structures form in the coldest parts of the atmosphere -- around 76 to 85 kilometers (47 to 53 miles) up. They are composed of ice crystals that usually appear blue because of the absorption of red wavelengths of light by the Earth's ozone layer.
The exact causes of noctilucent clouds aren't yet known but it's been reported they are growing more common, leading some researchers to believe they may be affected by climate change.