Posted on Friday 31 October 2003

Astronaut Yang Liwei returned home on Wednesday a national hero after becoming the first Chinese person to enter space.

But the public, and Communist leaders, were left nonplussed after he told state TV he could not see the Great Wall of China from space.

"Is it true you can see the Great Wall of China from space?" asked a TV interviewer.

"Er, no," he replied, a little embarrassed.

The Chinese have been proud of the fact that legend has it the 2,000-year-old wall is the only man-made object that can be seen from space.

Only it can't, according to Nasa.

They say their astronauts have failed to spot it and Liwei's assertion appears to be the final brick in the wall for the claim.

It is thought the myth may have begun during the early days of the space race.

[China's Wall not so Great]

Firstly, it is not true that the Great Wall is the only manmade structure visible from space. In fact a great number of manmade structures are visible including cities, highways and with the aid of binoculars even the Great Pyramids of Giza.  The irony is that when compared to these other manmade structures, the Great Wall is much harder to see.

The difficulty with the Great Wall is that much of it was made from materials which are very similar in color to the surrounding countryside and that much of the wall (those bits not walked on by tourists i.e. nearly all of it) is in quite poor condition, looking in places more like a long pile of rubble rather than an actual wall.

The other problem is that it's quite narrow with an average width of only 5 metres. From Yang Liwei's perspective, flying at an altitude of more than 200 kilometres, the Great Wall's apparent width would be only about 5 seconds of arc.  The moon by way of comparison is 30 minutes of arc (that's 360 times bigger) and much much brighter. Compounding Yang's problem is the fact that his space capsule was moving incredibly quickly, orbiting the earth 14 times in his 21 hours in space and for at least half of that time China would have been in complete darkness.

So is the wall visible from orbit or not? The answer is "yes" but it's very hard to see and probably can't be seen at all without the aid of binoculars.

Here is a selection of opinions from various astronauts about the visibility of the Great Wall of China from orbit:

Astronaut William Pogue orbited the Earth in the Skylab space station, in 1973 to 1974. The altitude was about 300 miles above the Earth. Pogue wrote that he could see the Great Wall if he used binoculars. It was not visible to the unaided eye, however.

Space Shuttle Astronaut Jay Apt reported the following: "We look for the Great Wall of China. Although we can see things as small as airport runways, the Great Wall seems to be made largely of materials that have the same color as the surrounding soil. Despite persistent stories that it can be seen from the moon, the Great Wall is almost invisible from only 180 miles up!"

It turns out you can see an awful lot from space. You can see the Great Wall. I've been trying, thus far unsuccessfully, to take a nice picture of it. The reason being that I haven't been successful is that the weather hasn't cooperated. There has been a lot of clouds and haze over that area since I've been trying. But I hope to be successful before I come back down.

You can see, for instance, cities quite easily. Islands, of course, are very easy to spot, and on islands, of course, it is usually easy to spot the main cities there.

If you look carefully you can actually see manmade structures. For instance, you can see the pyramids from space, especially with a pair of binoculars. They are a little difficult to pick out with just your eyes. With binoculars you can see an awful lot of things. You can see roads. You can see harbors. You can even see ships; very large tankers on the ocean we can see using the binoculars. You can see airplane contrails, and occasionally at the end of an airplane contrail, you will see a glint of sunlight off the airplane.