January 17, 2011

Really, The Great Wall of China is the only manmade object visible by unaided (naked) eyes from the moon or space?

FDI publication’s “Around D Word” book states that, there are only 2 artificial objects which can be seen from space, one is Kansai Airport which is located at Japan and other is The Great Wall of China. Then I started quizzing myself about this. I am putting some finding of my investigation.
Little background about this rumor/misconception/myth,
Þ In 1754, English antiquary William Stukeley wrote in letter, “This mighty wall of four score miles in length (Hadrian's Wall) is only exceeded by the Chinese Wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the moon”
Þ Similar kind of reference found in American-published magazine The Century in 1893
Þ In 1895, Henry Norman states "besides its age it enjoys the reputation of being the only work of human hands on the globe visible from the moon."
Þ In 1932, it was appeared publicly in “Ripley’s Believe It Or Not” cartoon
Þ In 1938, Richard Halliburton's book “Second Book of Marvels” assured readers that The Great Wall could be seen from space and claimed that it was the only man-made structure visible from the moon
This claim was made long before the first man-made satellite, Sputnik, was sent into orbit, and 31 years before humankind had set foot on the moon.
The answer of the above myth:
In case of moon the answer is NO.
The wall is a maximum 9.1 m (30 ft) wide, and is about the same color as the soil surrounding it. Based on the optics of resolving power (distance versus the width of the iris: a few millimeters for the human eye, meters for large telescopes) only an object of reasonable contrast to its surroundings which is 70 mi (110 km) or more in diameter (1 arc-minute) would be visible to the unaided eye from the moon, whose average distance from Earth is 384,393 km (238,851 mi). The apparent width of the Great Wall from the moon is the same as that of a human hair viewed from 2 miles away. To see the wall from the moon would require spatial resolution 17,000 times better than normal (20/20) vision.
In 2001, Neil Armstrong stated about the view from Apollo 11: "I do not believe that, at least with my eyes, there would be any man-made object that I could see. I have not yet found somebody who has told me they've seen the Wall of China from Earth orbit. ...I've asked various people, particularly Shuttle guys, that have been many orbits around China in the daytime, and the ones I've talked to didn't see it."
Apollo 12’s astronaut Alan Bean: "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."
In case of space the answer is hazy.
Actually, answer of this question is depends on, what do we mean by SPACE? If we take "space" to mean a low Earth orbit (160 km), even though its visibility from that distance is questionable.
Some claims that, we can see it from this distance with naked eyes. U.S. Senator Jake Garn claimed that he was able to see the Great Wall with the naked eye from a space shuttle orbit in the early 1980s, but his claim has been disputed by several U.S. astronauts. Veteran U.S. astronaut Gene Cernan has stated: "At Earth orbit of 100 miles (160 km) to 200 miles (320 km) high, the Great Wall of China is, indeed, visible to the naked eye." Ed Lu, Expedition 7 Science Officer aboard the International Space Station, adds that, "it's less visible than a lot of other objects. And you have to know where to look."
But other authors have argued that, due to limitations of the optics of the eye and the spacing of photoreceptors on the retina, it is impossible to see the wall with the naked eye, even from low orbit, and would require visual acuity of 20/3 (7.7 times better than normal).
Kamlesh P. Lulla, NASA's chief scientist for Earth observation at Johnson Space Center in Houston, directs observation science activities from the Space Shuttle and the International Space Station. He says that generally the Great Wall is hard to see and hard to photograph, because the material from which it is made is about the same color and texture as the area surrounding it. It's questionable whether you can see it with the unaided eye from space. "The shape, the age of the structure, the resolution of the camera, the condition of the atmosphere -- all these factors affect the ability to detect an object from space." But, he added, "you can see the wall in radar images taken from space."
On the whole issue NASA says “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.

To conclude, The Great Wall of China is not visible from either moon or space.
The Beijing Times added, "Having this falsehood printed in our elementary school textbooks is probably the main cause of the misconception being so widely spread."
According to the BBC, "For decades, elementary schoolbooks have maintained that the Great Wall of China could be seen from space - but now the books are being rewritten."
But in India, such wrong information spreading is still going on…
(This article is written on 12-01-2011)

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