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This is a composite photo of the Earth at night.  We think it is interesting because it  illustrates how concentrated our global energy resources and consumption patterns are.  The need, and the opportunities, for utilizing more distributed forms of renewable energy are vast.  Figuring out how to develop these resources is one of the key challenges our world will be facing this century.

Human-made lights are concentrated on developed areas of the Earth's surface. Notice the "lit up" seaboards of Europe, the eastern United States, and Japan. Also notice that many large cities are located near rivers or oceans, which facilitate trade.

The brightest areas of the Earth are the most urbanized, but not necessarily the most populated. (Compare western Europe with China.) Cities tend to grow along coastlines and transportation networks. Even without the underlying map, the outlines of many continents would still be visible. The United States interstate highway system appears as a lattice connecting the brighter dots of city centers. In Russia, the Trans-Siberian railroad is a thin line stretching from Moscow through the center of Asia to Vladivostok. The Nile River, from the Aswan Dam to the Mediterranean Sea, is another bright thread through an otherwise dark region.  Although the Eastern U.S., Europe, and Japan are brightly lit by their cities, many regions are still thinly populated and unlit. Antarctica is entirely dark. The interior jungles of Africa and South America are mostly dark, but lights are beginning to appear there. Deserts in Africa, Arabia, Australia, Mongolia, and the United States are poorly lit as well (except along the coast), along with the boreal forests of Canada and Russia, and the great mountains of the Himalaya.

The image was created with data from the Defense Meteorological Satellite Program's (DMSP) Operational Linescan System (OLS). This network of satellites was originally designed to pick up on lunar illumination reflecting off of clouds at night in order to aid nighttime aircraft navigation.  What the Air Force discovered is that on evenings when there was a new moon, the satellites were sensitive enough to record the illumination from city lights. Over a period of several new moons, the data the satellites retrieved could be pieced together to produce a global image of city lights.  This image is a composite of hundreds of pictures made by orbiting satellites.