View from space of polar mesospheric clouds over the earth's southern hemisphere, January 30, 2010. These clouds occur over the high latitudes of both hemispheres during their summer months at very high altitudes. Also known as noctilucent ("night-shining") clouds, they exhibit thin, wispy light blue forms that contrast with the darkness of space. Clouds closer to the earth's surface are more strongly illuminated by the sun and appear orange to white.