NASA recently published a wonderful image (Fig. 1) of the night side of Earth, acquired by an astronaut, aboard the International Space Station (ISS), Earth’s largest artificial satellite, orbiting at an altitude of about 350 km. The image, obtained on 4 December 2011, shows the Iberian Peninsula and parts of North Africa and Western Europe.
In the image, the city lights of Spain and Portugal define the Iberian Peninsula. Several large metropolitan areas are visible, marked by their relatively large and brightly lit areas, including the Spanish capital city, Madrid, located above image center, and Lisbon, capital of Portugal, located lower left of center. This astronaut view is looking toward the east, and is part of a time-lapse movie.
The network of smaller cities and towns along the coasts and in the interior demonstrates the extent of urbanization in Iberia. The blurring of city lights is caused by thin cloud cover (image left and center), while cloud tops are dimly illuminated by moonlight. The lights of France glow near the horizon (limb of Earth) on the upper left, while the lights of northern Africa are more clearly visible. The faint gold and green lights, running parallel to Earth’s limb, are airglow, induced by solar ultraviolet radiation, exciting gas atoms and molecules in the upper atmosphere.
References
NASA’s Earth Observatory
http://earthobservatory.nasa.gov/IOTD/view.php?id=76777
Johnson Space Center
www.jsc.nasa.gov/
International Space Station
http://www.nasa.gov/mission_pages/station/main/index.html