WIKIARCHIVES.SPACE

View taken by STS-117 crewmember on Space Shuttle Atlantis. In the summertime in the far northern or southern latitudes, high in the Earth’s atmosphere at the edge of space, thin, silvery clouds sometimes become visible just after sunset. These high clouds, occurring at altitudes of about 80 kilometers (50 miles), are called polar mesospheric clouds (PMCs). They are also called noctilucent (“night-shining”) clouds.