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A nighttime view of Tokyo, Japan from the International Space Station. The heart of the city is brightest, with ribbons of lights radiating outward from the center along streets and railways. The regularly spaced bright spots along one of the ribbons heading almost due west out of the downtown area are train stations along a public transit route. The lights of Tokyo are a cooler blue-green color than in many other world cities. The color results from the more widespread use of mercury vapor lighting as opposed to sodium vapor lighting, which produces an orange-yellow light. Photo: NASA.