In a Nutshell
Contrary to popular belief that the Great Wall of China is the only man made structure that can be seen from space, astronauts have often reported that in fact zero man made structures, including the Great Wall, can be seen beyond Earth’s immediate atmosphere.
The Whole Bushel
Perhaps the most famous fact about the Great Wall of China is that it is the only man-made structure that can be seen from space. Unfortunately, that’s not an actual fact. Astronauts have been quoted saying that zero man-made structures are viewable from space, unless you count the millions of lights that illuminate landmasses on the night side of the Earth.
It turns out that the whole “it can be seen from space” thing came about before we ever actually had the capability to find out for ourselves whether or not it was true. At best, astronauts say that it’s impossible to see any structures at all beyond 180 miles above the Earth’s surface, and those structures do not include the Great Wall.
In fact, astronauts are more likely to see airport runways from the Earth’s atmosphere than the Great Wall. It looks like this misconception first gained popularity when a few different writers just decided to claim it as truth, as far back as a 1904 claim by Henry Norman.
Show Me The Proof
NASA: Space Station Astrophotography
Snopes: Great Walls of Liar