This is one of the most popular and widely circulated ‘facts’ related to space exploration, but it is in fact false on two levels. First, the Great Wall of China is NOT visible from space. Second, there are in fact some man-made structures that are visible from space. So, wherever or whoever this myth originated from, there is some serious justification needed!
The myth probably originated some time in the 19th century, when we humans were discovering the canals on Mars for the first time. This led us to believe that long, straight objects or patterns are visible from great distances. While the idea seemed plausible at the time, the myth has been debunked several times since. The Great Wall of China is visible from up to a few kilometres above the Earth’s surface, it is not visible from the International Space Station (which orbits at around 200 km from the surface) and certainly not from the moon (which is around 384,400 km away), as some people have claimed.
NASA confirmed that in 2004, an astronaut called Leroy Chiao took the first image of the Great Wall from the International Space Station. Here it is.
The above image was taken with a 180 mm zoom lens. That means that it does not represent what the naked eye would see. Can you spot the Great Wall in the image? Of course not. If you cannot see the Wall in a zoomed image, what chance is there that you would be able to see it with your naked eye? Almost nil. In case you are still looking for the Wall, check out this website. The Wall has been marked out on a cropped version of the image. The Wall is difficult to see because it is built along the contours of the landscape, and there is no contrast with the surroundings.
Even though the Great Wall of China is not visible from space, there are some man-made structures that are visible. Astronauts have said that the ancient pyramids at Giza are relatively easy to see. Another example are the greenhouses in province of Almeria, Spain. They cover almost 200 square kilometres, and can be easily identified from space due to the stark contrast with their surroundings.
Perhaps surprisingly, even some roads and bridges are visible from space. This often happens when the road or bridge crosses rough terrain, as shown in the example below. The straight, black line on the left is in fact a road and is easily visible because of the roughness of the surrounding terrain.
At night, entire cities become visible easily from space because of the light they produce. In the image below, the entire Iberian peninsula (Spain and Portugal) is shining with lights.
There are several other examples of man-made structures that are visible from space, including mines, fields and palaces.
It is amazing how some false facts can gain immense popularity among the masses. We must not perpetuate this myth any further.