Wednesday, 19 September 2012

THE GREAT WALL MYTH : wall is not

 visible from outer space

It is common mistake to say that The Great wall of China is visible from outer space. It is too thin to be noticed from such a great distance. There are no man made structures that are visible from space or moon. Man made objects start to disappear after 300 miles up. From that distance you can barely see the outline of the Great China Wall. If we consider that distance from Earth to Moon is around 384,403 kilometers/238,857 miles then we can draw reasonable conclusion that it would be impossible to see any man-made structures from such a distance. Astronaut Alan Bean said: "The only thing you can see from the moon is a beautiful sphere, mostly white (clouds), some blue (ocean), patches of yellow (deserts), and every once in a while some green vegetation. No man-made object is visible on this scale. In fact, when first leaving earth's orbit and only a few thousand miles away, no man-made object is visible at that point either."

It has become a space-based myth. The Great Wall of China, frequently billed as the only man-made object visible from space, generally isn't, at least to the unaided eye in low Earth orbit. It certainly isn't visible from the Moon. 

You can, though, see a lot of other results of human activity. 
Expedition 10 photo showing Great Wall of ChinaThe visible wall theory was shaken after China's own astronaut, Yang Liwei, said he couldn’t see the historic structure. There was even talk about rewriting textbooks that espouse the theory, a formidable task in the Earth’s most populous nation. 

Image to right: This photo of central Inner Mongolia, about 200 miles north of Beijing, was taken on Nov. 24, 2004, from the International Space Station. The yellow arrow points to an estimated location of 42.5N 117.4E where the wall is visible. The red arrows point to other visible sections of the wall. Credit: NASA.
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The issue surfaced again after photos taken by Leroy Chiao from the International Space Station were determined to show small sections of the wall in Inner Mongolia about 200 miles north of Beijing. 

Taken with a 180mm lens and a digital camera last Nov. 24, it was the first confirmed photo of the wall. A subsequent Chiao photo, taken Feb. 20 with a 400mm lens, may also show the wall. 

The photos by Chiao, commander and NASA ISS science officer of the 10th Station crew, were greeted with relief and rejoicing by the Chinese. One was displayed prominently in the nation's newspapers. Chiao himself said he didn't see the wall, and wasn't sure if the picture showed it. 
Radar image of Great Wall of ChinaImage above: While the Great Wall of China is very difficult to see or photograph from low Earth orbit, sections of the wall can be seen readily in radar imagery. This image of sections of the wall in a desert about 435 miles west of Beijing was made by the Spaceborne Imaging Radar flown aboard the Space Shuttle Endeavour. The wall appears as an orange line extending the length of the image. Credit: NASA. 

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