Earth Observations taken by the Expedition 22 Crew ISS022-E-052281 (30 Jan. 2010) --- Polar mesospheric clouds over the Southern Hemisphere are featured in this image photographed by an Expedition 22 crew member on the International Space Station. This striking view shows polar mesospheric clouds (PMC) over the polar region of the Southern Hemisphere. These clouds occur over the high latitudes of both northern and southern hemispheres during their respective summer months at very high altitudes of approximately 76?85 kilometers. When present they are visible during twilight, when the clouds are illuminated by the sun while the ground surface below is in darkness. The International Space Station (ISS) orbit extends from latitude 52 North to latitude 52 South; combined with the highly oblique views through Earth?s atmosphere possible with hand-held imagery, the ISS is an ideal platform for documenting these transient, high altitude phenomena. Another NASA mission, the Aeronomy of Ice in the Mesosphere or AIM satellite, is dedicated to the study of PMC and is providing daily information about their formation, distribution, and variability. Polar mesospheric clouds are also known as noctilucent or night-shining clouds ? a property that is clearly visible in this photograph. The PMC exhibit thin, wispy light blue forms that contrast with the darkness of space above (upper right). Lower levels of cloud are strongly illuminated by the sun and appear light orange to white. Clouds closest to Earth?s surface are reddish-orange (center). The image was taken approximately 38 minutes after midnight Greenwich Mean Time (GMT) while the ISS was located over the southern Atlantic Ocean. At this time of year, the sun never sets over Antarctica but rather defines an arc across the local horizon, allowing PMC to be observed near local midnight.
