According to astronauts, it's actually quite difficult (if not impossible) to see the Great Wall of China from space, as it blends in with the surrounding land. It's also impossible to discern anything man-made on Earth while on the moon-the distance is too great. When people say that something is visible from "space," they typically mean from the distance of an orbiting space shuttle or space station.
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Key Facts In This Video
Satellites have been taking photographs of Earth since 1972. 00:01
Even economic events such as the recession are visible from space, as they might noticeably halt the growth of cities. 01:31
Receding ice shelves indicate climate change. 02:00