Is the Great Wall of China visible from space?

For practical purposes, no. The claim that the Great Wall is the only human-made object visible from space is a myth. NASA says the wall is not visible from the Moon and is difficult or impossible to see from Earth orbit without the high-powered lenses used for photographs. Astronauts, including China's first, Yang Liwei, have reported being unable to see it. [1] [2]

Writing in Scientific American, Phil Plait says the basic problem is resolution, the ability to tell closely spaced objects apart. The average human eye resolves about one arcminute. One of the wider parts of the wall might be 10 meters across. From the Moon it would appear as a line one ten-thousandth of an arcminute thick, roughly like seeing a human hair from a kilometer away. From the International Space Station, about 400 km up, it would span about 0.1 arcminute, still too small for the eye. [3]

Contrast is a second problem. Long, narrow, high-contrast features such as desert roads and ship wakes can be seen from orbit, but the wall is built of stone that generally blends into the terrain, and it curves with the landscape. NASA's Kamlesh Lulla made the same point, saying the materials are similar in color and texture to the surrounding dirt. [3] [4]

Photographs exist, but they rely on long lenses. Leroy Chiao photographed sections of the wall in Inner Mongolia from the ISS on 24 November 2004 with a 180mm lens, described by NASA as the first confirmed photo of the wall. Chiao himself said he did not see the wall and was not sure the picture showed it. NASA's Lulla said a sunny day and recent snowfall probably helped make the wall visible. In 2018 ESA astronaut Alexander Gerst used an 800 mm lens and called the wall next to impossible to see with the naked eye and still tough to spot even with the lens. [4] [5]

Canadian astronaut David Saint-Jacques said in 2019 that he tried and could not see it. He suggested the wall's being built in separate sections, like a dotted line, makes it harder to spot. [6]

One source says the myth dates to at least 1938, before anyone could test it, and that its originator is unclear. It was speculation rather than observation. Some conditions may help detection: Plait notes that a low sun at sunrise or sunset can make the wall cast a long shadow, though that reveals the shadow rather than the wall itself. Radar imagery from space, such as that from the Space Shuttle Endeavour, shows sections of the wall clearly as a line. [2] [3] [4]