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In the daytime, humanity’s footprints on Earth are visible in numerous ways, even from space: the geometric patterns of our croplands, lush golf courses springing up from the desert like manmade oases, decades of river flow captured in reservoirs behind massive dams. When the Sun goes down, however, only one kind of footprint remains visible: our cities.

Images of city lights at night taken by astronauts are among the most interesting visual reminders of how humans have transformed Earth’s surface. This nighttime photograph of Tokyo, Japan, was taken by International Space Station astronaut Dan Tani on February 5, 2008. 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 probably train stations along a public transit route. The lights of Tokyo are a cooler blue-green color than 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.

In honor of Earth Day 2008, the International Space Station Crew Earth Observations Experiment and the Image Science & Analysis Laboratory at Johnson Space Center published a new set of nighttime images, which are featured in the Earth Observatory article Cities at Night: The View From Space.

The teams also released an animated “world tour” of cities at night [high-resolution (126 MB MPEG), web-resolution (39 MB QuickTime)], created by astronaut Don Pettit from a sequence of several of the most striking images of city lights at night.

Astronaut photograph ISS016-E-27586 is provided by the ISS Crew Earth Observations experiment. The image was taken by the Expedition 16 crew, and is provided by the Image Science & Analysis Laboratory, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by Rebecca Lindsey.