A Thought Experiment: Technology Meets the Great Wall

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A reader in Australia writes with a problem:

So, supposedly, the Great Wall of China is visible from space. But apparently it's not. Recently, I've discovered that both sides claim credibility (rather than one being an urban legend like the slowly boiling frog). I want to know if it's true.

The tallest and widest part of the wall is 9.1m wide (tapered to 3.7m) and 8m high. It's 6400km long, but much of that is significantly thinner than 9.1m. (According to Wikipedia).

Anyway, would such an object be discernible with the unassisted eye, on a clear, cloudless, pollutionless day, from Low Earth Orbit (2000km), or Geostationary Orbit (26000km) or somewhere in between (say 12000km)?

The most plausible answer I've been given is that you can see the Wall in the sense that because it's such a long continuous feature, especially with the correct shadow conditions, you can easily ascertain where it is if you know it's there somewhere. However, there was some debate as to whether this counted as 'seeing' - if an adult human that knew nothing about the Wall were in a shuttle looking out the window, would they go "Oh hey look! A wall!"?

The Great Wall, in Gansu province, not from space but from ground level.

GansuWall.jpgThanks to the Miracle of Technology, there is actually a way to answer this question beyond a reasonable doubt in the comfort of your home. I'll mention it as an aside in a day or two. Determining the truth of the boiling frogs was more difficult.  

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James Fallows is a national correspondent for The Atlantic and has written for the magazine since the late 1970s. He has reported extensively from outside the United States and once worked as President Carter's chief speechwriter. His latest book is China Airborne. More

James Fallows is based in Washington as a national correspondent for The Atlantic. He has worked for the magazine for nearly 30 years and in that time has also lived in Seattle, Berkeley, Austin, Tokyo, Kuala Lumpur, Shanghai, and Beijing. He was raised in Redlands, California, received his undergraduate degree in American history and literature from Harvard, and received a graduate degree in economics from Oxford as a Rhodes scholar. In addition to working for The Atlantic, he has spent two years as chief White House speechwriter for Jimmy Carter, two years as the editor of US News & World Report, and six months as a program designer at Microsoft. He is an instrument-rated private pilot. He is also now the chair in U.S. media at the U.S. Studies Centre at the University of Sydney, in Australia.

Fallows has been a finalist for the National Magazine Award five times and has won once; he has also won the American Book Award for nonfiction and a N.Y. Emmy award for the documentary series Doing Business in China. He was the founding chairman of the New America Foundation. His recent books Blind Into Baghdad (2006) and Postcards From Tomorrow Square (2009) are based on his writings for The Atlantic. His latest book is China Airborne. He is married to Deborah Fallows, author of the recent book Dreaming in Chinese. They have two married sons.

Fallows welcomes and frequently quotes from reader mail sent via the "Email" button below. Unless you specify otherwise, we consider any incoming mail available for possible quotation -- but not with the sender's real name unless you explicitly state that it may be used. If you are wondering why Fallows does not use a "Comments" field below his posts, please see previous explanations here and here.
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