Reports of Earth-orbiting astronauts glimpsing the Great Wall of China and many other artificial structures are wildly exaggerated, but humanity’s planetary influence isn’t entirely invisible from afar
When I was a mere lad, probably in middle school, I remember a friend telling me that the Apollo astronauts could see the Great Wall of China from the moon.
Resolution is usually expressed in terms of an angle that is determined by the size of the object and its distance from the observer. For a concrete example, the moon is about 3,500 kilometers wide and 380,000 km away from Earth;and you’ll find that the moon appears to be about 0.5 degrees across . At that distance, the Great Wall would appear as a line one ten-thousandth of an arcminute thick. Resolving that feature would be roughly the equivalent of seeing a human hair from a kilometer away with your unaided eyes. I think you’ll agree that that’s flatly impossible!
Sadly, no. The Great Wall is made of stone that generally doesn’t contrast well against the terrain, and it tends to curve as it follows the landscape, especially near steep cliffs and hills.are captured using a telephoto lens, which has a much higher resolution than the human eye.) Even China’s first taikonaut, Yang Liwei,detectable from orbit. For example, when the sun is low in the sky at sunrise or sunset, the wall can cast a long shadow, revealing its presence.
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