Today I am going to be talking about one of the most scientifically ridiculous memes in popular culture. Most people seem to believe that the Great Wall of China (http://en.wikipedia.org/wiki/Great_Wall_of_China, if you have lived under a rock your whole life) is the only man-made object visible from space, or from the moon, depending on your myth. It has appeared in every fact book or app I have ever read, and is one of the most popular myths in society. However, this myth is wrong on almost every conceivable level, which I will delve into today.
The level most impossible in this story is the idea that the Great Wall of China is the largest man-made object on earth. Even if it is true that the Great Wall of China is visible from space, the moon, or where ever, the Great Wall is not going to be the only thing visible. Consider the Great Wall of China. It is a pale white-brown coloured wall, and is, in the stretches of best condition, a few meters wide and in reasonable condition. It is very, very long, and in the bad stretches it is no more than rubble remains, in some stages. The Wall, when viewed from above, is a pale brown colour on a backdrop of green or brown mountainous area. This in itself points out something, a brown coloured anything on a similarly coloured background, is not going to be clearly visible from any reasonable distance, due to a low contrast.
Now consider other things which are of similar shape and/or size. A four or six lane highway, large buildings like the pentagon, and sports stadiums are all wider than the great wall of china, and would be sighted quicker due to their greater contrast in background. A 6 lane highway is black, on an often light or grey coloured background, the pentagon is grey on a green background, and sports fields are green and often situated in cities, grey in colour. So it is clear that the Great Wall of China is not the most contrasting in its background, or the largest man-made object around. So there are things more visible from afar than the Great Wall.
The second problem with this myth, is the facts. The two myths being questioned here, both have different answers on this subject. The Great Wall of China is NOT visible from the moon, but is visible from low earth orbit, just like highways and buildings.
The third speed-bump in this myth is the definition of space, a big question, with no real answer. I have already mentioned one possible definition of space, low earth orbit, the orbit which is taken by the space shuttle and others, allowing for orbit of the earth every 90 minutes. Another definition would be when 99% of the earths atmosphere is below you, then you would be in space. It could be the geostationary orbit taken by our GPS satellites. There are many possible choices, and the point is, space is not clear-cut, so when a claim is made about something being visible from space, you have to ask which space it is visible from.
The myth that the Great Wall of China is visible from the moon is ridiculous, while the idea that the Great Wall of China is visible from space is very blurry, and is only visible along with all of the other big things we have made.