Polar mesospheric clouds, ISS image. Photograph of polar mesospheric clouds from the northern hemisphere taken by astronauts aboard the International Space Station (ISS). Polar mesospheric clouds, also known as noctilucent or 'night-shining' clouds, are the highest clouds in the Earth's atmosphere. Made from water ice, these clouds form 76-85 kilometres above the surface and are visible in deep twilight when illuminated by the sun just below the horizon. The dim orange glow just above the horizon is the Earth's stratosphere. Photographed 13th June 2012.