Dr Karl › Dr Karl's Great Moments In Science

Great Wall of China from space (Part II)

Last time Dr Karl dispelled some of the myths that have grown up around The Great Wall Of China - concerning its history and its current state of repair. This time Dr Karl takes on the tallest tale that is told about the Great Wall...

It's claimed that you can see the Great Wall of China from the Moon.

That's one big claim, but let's take this apart brick by brick.

Last time, I pointed out that the Great Wall of China is not actually one huge monolithic wall of great structural integrity, but a whole bunch of walls. Some sections (especially the bits that the tourists visit) appear to be in really mint condition – but they were totally rebuilt in the 1950s.

Some bits have decayed so much that there's not even a mark in the dirt to show where the original structure was.

But what about the claim that you can see it from the Moon?

It seems to have begun with the American traveller William Edgar Geil in 1909. He wrote a book The Great Wall of China, and in it, claimed that you can see the Great Wall from the Moon. And that as in 1909, long before Space Travel.

Then in 1923, Adam Warwick wrote in the National Geographic, "According to astronomers, the only work of man's hands which would be visible to the human eye from the Moon is the Great Wall of China".

Joseph Needham went even further - all the way to Mars. He wrote in Vol. 4 of his multi-volume work Science and Civilisation in China in 1971 on page 47, "stretching from Chinese Turkestan to the Pacific in a line of well over 2000 miles (nearly a tenth of the Earth's circumference), the Wall has been considered the only work of man which can be picked out by Martian astronomers."

Many other authors, publicists for travel agencies and even the drunk guy down at the pub kept on repeating this story. But is it true?

Neil Armstrong, the first man to walk on the Moon, said about the Great Wall of China, "It is not visible from lunar distance". Edwin "Buzz" Aldrin, his co-pilot said, "you have a hard time even seeing continents."

So we can't see the Great Wall from the Moon, which is about 400,000 km away. But could you see it from the Space Shuttle? It flies in Low Earth Orbit, 300-530 kilometres up.

The astronaut William Pogue, who flew in space on Skylab 4, was able to see the Great Wall, but only with binoculars, and with lots of practice.

The American astronaut Sally Ride talked about how the high speed of the Space Shuttle makes it very difficult to see anything down on the ground.

"I found that at this speed (five miles per second), unless I kept my nose pressed to the window, it was almost impossible to keep track of where we were at any given moment - the world below simply changes too fast."

Karl Henize flew on Space Shuttle 51F in July 1985 - and he too failed to see the Great Wall from orbit. The Space Shuttle is so fast that Karl Henize had only a very short time to look for the Wall.

Afterwards, he wrote, "There is little time for map reading - from the time an approaching area is 45 degrees from the (vertical) - at which time one can begin to make out a fair amount of detail - until it is slipping under the spacecraft hull is 40 seconds at most."

The astronaut Andy Thomas wrote about recognising objects on Earth on May 22, 1998, while he spent 141 continuous days on the Russian Space Station Mir.

He wrote how striking was "the abundance of clouds". After a while, he could recognise the deserts of Northern Africa, the redness of Australia and characteristic coast lines such as the "boot" of Italy.

But even though he tried, he was never able to see the Great Wall. He wrote about the extreme difficulty in recognising Earthly objects from orbit.

He tells us, "Cities can be seen, although, surprisingly, they do not stand out readily. But we can make out their grid-like pattern of streets. The stories about the Great Wall of China being visible from space may be true, but I have yet to see it".

Imagine looking out of a third-storey window, trying to see a very long fishing line on the ground - you can't. It doesn't matter how long the fishing line is. It's simply too skinny to be seen. Same with the Great Wall of China.

The astronaut James Lovell said that, with the naked eye, he could recognise El Paso airport from orbit, because he had flown over it many times in various aircraft.

But he could not recognise the similar-sized airport at Kinshasa in Zaire even though he knew where to look - because he was not familiar with it.

So maybe Chinese astronauts in the future will report that they can see the Great Wall of China from Space with the naked eye, but so far, nobody has.

^ to top