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Europe at night. Satellite image of the Earth seen at 00:00 (midnight) GMT (UTC), centred on Europe. City lights (yellow) in dark areas show areas of dense population, particularly in North America (upper left). Africa (lower centre) and the Arctic (top) are sparsely populated and so have fewer lights. Image obtained using data from Landsat 5 and Landsat 7 satellites. (KEYSTONE/SCIENCE PHOTO LIBRARY/PLANETOBSERVER)