At some point it became a commonly known 'fact' that the Great Wall Of China is the only manmade structure visible from space. However this supposedly unassailable common knowledge really doesn't stand up to scrutiny - especially when you actually try to spot it from space.
Even without images, just thinking about the logistics of this factoid doesn't quite add up. With 21,196 km of fortifications the wall is an impressive structure, and parts of it look monumental from the ground, but despite its length the wall is still less than 10 meters wide even at its widest. Add to that the fact that it's generally made from local stone, the same colour of the terrain around it, and it's actually pretty difficult to see the wall from space.
For example, can you pick the wall from this satellite image?
If you look closely you'll see a tiny thin line from the bottom left to the top right of the image. However the river that runs from the top left to bottom right is far more prominent.
In forested areas it's a little easier to pick out. Check this shot out:
You can see the wall running along the ridge just to the left of the centre of the image - but note that the clusters of towns to the right are far more prominent than the tiny little wall.
Yes, that's right, there are actually a lot of manmade structures that are visible from space. Most cities are distinct at day and ostentatious at night due to their lights, while other structures like solar farms, open mines and industrial complexes are easily distinguished.
People who have actually been in space to debunk this fact, astronauts Eugene Cernan and Ed Lu, have said that the wall can be visible from low Earth orbit (where the ISS orbits) but only when conditions are good.
So where did this myth come from? It actually originated before humans had even gained the power of flight, let alone spaceflight. In 1754 an Englishman named William Stukeley wrote that Hadrian's wall was "only exceeded by the Chinese Wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the Moon."
Considering Stukeley had never actually been to the moon, it's no surprise this factoid turned out to be a whole lot of bull, but it has persisted in pop culture to the modern day. Thanks, William.
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