Can The Great Wall Be Seen From Outer Space?

Urban legend or truth? I have heard over-and-over that the Great Wall of China is the only man made structure that can be seen from the Moon. There are problems with this statement. Despite its extra-ordinary length of around 1,500 miles, the wall isn't particularly wide.

The width and height of some sections are impressive. The average dimensions are roughly 6 meters (18 feet) wide and 8 meters (25 feet) high. The watchtowers normally add about 4 meters (13 feet) to the height.

So, if one uses a thread as a proxy, it doesn't matter how long the thread is, the critical variable is its width. And at one point, despite its length, as you travel away from the thread, you will not be able to see it.

From the moon, given its distance and given a relatively clear day, an object with a width of around 0.4 miles across could be seen. A definitive debunking can be found here.

So, therefore, given the width of the Great Wall, there is some point in the space between the Earth and the Moon where the Wall can be seen. But then again, at that point, many other man-made objects of large dimensions can be seen too. Some parts of the Panama Canal are 36 meters [about 100 feet] wide but only around 50 miles long and the Suez Canal is around 190 feet wide and around 100 miles long. And many of the highways, bridges and other modern structures are of a width large enough to be seen too.

In any case, it was a truly extraordinary feat of engineering to build the Great Wall of China over 2,000 years ago. But given the pollution problems in China, these days, there will be very little that can be seen from any greater distances than where a tour bus can take you.