We’ve got some news for you: the Great Wall of China is actually not visible to the naked eye from space, even in low-earth orbit, according to NASA.
This is surprising to many, as it’s long been circulated that the wall is visible from space, with many believing it’s the only man-made object detectable from space by the naked eye.
However, this isn’t actually true, and the visible wall theory was shaken after China's own astronaut, Yang Liwei, said he couldn’t see the historic structure from space.
This discovery even spurred discussions about rewriting textbooks that boasted the theory - a pretty controversial suggestion in the Earth’s most populous nation.
Why is the Great Wall of China not visible from space?
According to astronauts, no man-made objects are visible from space with the naked eye.
Not only this but even with the help of a space camera with a huge zoom capable of picking up fine details, the Great Wall of China is not necessarily the easiest man-made object to see.
The Great Wall has an awe-inspiring structure that spans some 4,500 miles (7,200 kilometers). However, despite its grandeur, it's constructed from materials that make it difficult to identify from space.
While the wall is very long, it’s also very thin, which makes it pretty much invisible from space. Even from a low Earth orbit, at an altitude that begins around 100 miles (160 kilometers), the wall is not easy to see.
This is largely due to the materials it’s made out of and the declining condition of the wall.
While sections of the wall near the capital Beijing have been restored for tourists, in many more remote areas of the country the structure is crumbling.
Even though the wall is still standing, the mixture of stone and clay easily blends into the surrounding land, making it very difficult to discern even from a low orbit.
The Egyptian pyramids, another grand structure from an earthly point of view, are further examples of significant man-made creations that tend to blend into their surroundings when astronauts have attempted to pinpoint them from space.
That said, there have been some alleged viewings of the wall from space, at least through a camera lens.
U.S. astronauts Eugene Cernan and Ed Lu claimed to have seen the wall from low orbit.
However, it seems that this depends largely on the light conditions, for example, when the sun is low on the horizon, the wall has been known to cast extended shadows that make it possible to discern its silhouette.
In 2004 American astronaut Leroy Chiao captured a photo from the International Space Station which seemed to depict a section of Inner Mongolia, around 200 miles (320 kilometers) north of Beijing, and it appeared to show a section of the Great Wall.
NASA experts confirmed that the wall seemed to appear in the photograph due to the favorable light conditions, however, even Chiao admitted that he wasn't sure what he was seeing from space.
Can satellites see the Great Wall from space?
Machines certainly have a better chance of capturing the Great Wall from space than the human eye does.
Low-orbit satellites have sensors that can see through haze and clouds, making it easier to produce clear images, yet even then it can be hit and miss when it comes to identifying the wall.
Their ability to view the wall is usually also dependent on light and weather.
Moderate-resolution satellites, like the U.S. Geological Survey's two operating Landsat satellites that orbit 438 miles (705 kilometers) above the Earth's surface, can generally only identify man-made structures in optimal weather conditions.
For example, in the past, snowfall around the Great Wall has enabled satellites to pick up the structure when the snow has been cleared from the wall but left in the surrounding areas.
This high contrast between the whiteness of the snow and the darkness of the wall makes it more visible.
What man-made structures are visible from space?
So, if the Great Wall of China isn’t visible from space, what is?
If you slowly zoom in using a space camera, Houston airport would actually be visible long before the Great Wall of China.
This is disappointing news for many, as sadly more often than not, it is the less impressive structures that stand out from space rather than the majestic cultural ones like the Great Wall.
Major highways that stick out prominently from large cities are typically the most visible for a camera to see from space. This is usually because of how the roads are created, for example, valleys are typically blasted through the hills to make way for the straight highways.
Desert roads are another man-made creation that tends to be easier to point out through a space camera than the Great Wall.
So there you have it: despite the much-loved myth that the Great Wall of China is the only man-made object visible from space, it’s not actually visible, even from a low orbit.
This is mainly due to the clay and stone materials the wall is made out of, and its long, thin structure that makes it blend in with its surroundings.
On rare occasions, space cameras and satellites have caught a glimpse of the ancient structure, however, these have been dependent on the light conditions and the weather.
It seems that the wall is sometimes visible if it’s highly contrasted; for example, if snowfall surrounds it but has been cleared from the wall so that it stands out against the white snow.
This makes sense as its usual grey clay and stone structure blends in with its surroundings under usual weather conditions.
Even so, it’s only a satellite that would be capable of capturing the image, and even satellite imagery is dependent on certain conditions.
It’s pretty surprising that some of the most awe-inspiring and impressive structures on Earth are not necessarily the easiest to see from space - and further reinforces just how tiny Earth is in the grand scheme of the universe.
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