Dr. W.T. Sullivan, an astronomer at the University of Washington, is interested in what human activity is visible from space. He assembled a collection of images of the Earth at night, taken by U.S. Air Force satellites. After a great deal of image processing, he reduced them to a common scale in order to construct a mosaic of the Earth at night. The resulting map is far more detailed than we can show here, where we have superimposed a miniature version of his work onto a darkened sphere and base map.
Much of the light leakage to space corresponds to street and building lights in urbanized regions, especially in Europe, North America, and eastern Asia. The delimiting effects of geographical features such as the Sahara Desert, the Himalayas, and the Australian Outback are also apparent. In the tropics, the major sources of light are controlled fires -- the result of grassland burning, slash-and-burn agriculture, and clearing of forests. The frequency of fires depends on season, but in the present image they are prominent throughout the highlands of Southeast Asia, the sub-Saharan savannas, and East Africa.
Other lights arise from huge burn-offs of natural gas associated with oil wells. Gas flares show clearly in Indonesia, the Tashkent region of Uzbekistan, Siberia, the Middle East, North and West Africa, and northwestern South America. In the Sea of Japan, the large blotch of light emanates from a fishing fleet that hangs multitudes of lights on its boats in order to lure squid to the surface.
The satellite photos were taken over the period 1974-84. The data from which the lights were derived originally came from U.S. Air Force / DMSP Archives, National Snow & Ice Data Center, NOAA, University of Colorado.
A two by three foot wall chart of Dr. Sullivan's Earth at Night is available for $6.50 plus shipping from Hansen Planetarium, in Salt Lake City, Utah. (800) 321-2369. A new image of North America at Night is also available.
