Can you see the Great Wall of China from space? Inquiring minds want to know.

There are many places where people have said that the Great Wall of China is the only man-made object you can see from space. This statement is definitely untrue. The Great Wall of China is a terrific engineering construction, but having been there, I can attest that at least two sections I’ve visited are only about 10 feet wide. At times it is perhaps 30 or 40 feet tall, but the average superhighway has four lanes which are 12 feet wide at a minimum. If you can see the Great Wall, you can certainly see a superhighway. So it’s not possible it can be the only man-made object you can see from space.

Some references to the Great Wall say that it is the only man-made object that can be seen from the moon. The first refutation is the width issue highlighted above. I also have to believe it is impossible for a human to see the Great Wall from the moon. The moon is approximately 180,000 miles from earth, or approximately 950 million feet from the Great Wall. That would mean a resolution of 10 feet at 950 million feet, or 95 million to one. I don’t think they make eye charts that small! 

The final question is, can you actually see the Great Wall from space? The math is a little more reasonable here -- the Great Wall is 10-12 feet wide, at times casting a shadow that might be perhaps 80 feet wide. The space shuttle, or any earth orbit space vehicle, orbits usually at an altitude of 100 to 200 miles, or half a million to one million feet. Yang Liwei, China’s first astronaut, said that he could not see the Great Wall from space. However, Gene Cernan, who has logged more than 556 hours in space according to Britain’s Guardian newspaper, is quoted as saying that it is all a matter of knowing where to look. He further is quoted, “If you know where to look and you look hard enough, you can also see the Astrodome in Houston, Texas where I live.” As the Astrodome would be quite a large object compared to the width of the Great Wall, this seems like a plausible statement. 

Some other man-made objects that seem likely to be visible from space:

• Hoover Dam
• The Panama and Suez Canals
• Any number of football stadiums and other sporting arenas
• Golden Gate Bridge (because of the contrast with the water, again also being quite a bit wider than the Great Wall).
• The Pyramids in Egypt (particularly considering the shadow that the would cast)
• Buildings in Manhattan or Tokyo

For sure, however, the Great Wall can’t be the only man-made object visible from space.

More discussion on this topic can be found on this fine page from about.com, another discussion on The Straight Dope, and more discussion on space.com