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A myth. Like spotting a hair from 3 km away.
Where it came from
The claim predates spaceflight: a 1932 Ripley’s “Believe It or Not!” cartoon said the Wall was the only human-made thing visible from the Moon. Once people had actually gone up, the legend simply moved to low orbit.
What’s actually true
The Wall is long but narrow, mostly under ten metres wide, and built of stone and earth the same colour as the land around it. From the International Space Station, about 400 km up, seeing it is roughly like spotting a human hair from three kilometres away.
China’s first astronaut, Yang Liwei, said in 2003 that he could not see it. Cities, airports, big roads and reservoirs are far easier to make out, especially at night.
Further reading
- NASA Earth Observatory, “Great Wall of China”
- Wikipedia: Great Wall of China (Visibility from space)