Richard Halliburton's book "Second Book of Marvels"
1938 said the Great Wall of China is the only man-made object visible from the Moon. This belief has persisted
today, assuming urban legend status, sometimes even entering school textbooks. Arthur Waldron, author
the most authoritative history of the Great Wall, has speculated that the belief might go back
the fascination with the "canals" once believed to exist
Mars. The logic was simple: If people
Earth can see the Martians' canals, the Martians might be able to see the Great Wall. But in fact, the Great Wall is only a few meters wide - similar in size
highways and airport runways - and is about the same color as the soil surrounding it. It cannot be seen
the unaided eye from the distance of the Moon, much less from Mars. If the Great Wall were visible from the Moon, it would also be apparent from near-Earth orbit, but from there it is barely visible, and only
nearly perfect conditions. The Great Wall of China is no more conspicuous
outer space than many other man-made objects.