Nasa accepted visible form space
from the lunar surface
There is a well-known but improbable myth that the Wall can be seen from the moon (385,000 km, 239,000 miles). An English antiquary named William Studeley wrote in a letter dated 1754 that "this mighty wall [Hadrian's wall] of four score miles [130 km] in length is only exceeded by the Chinese Wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the Moon." This is one of the earliest known references to the myth that the Great Wall can be seen from the Moon. Henry Norman made a similar claim in 1895, saying, "Without a doubt, its age contributes to its reputation as the only human-made object that is visible from the moon.
"The issue of Mars' "canals" gained prominence in the late 1800s and could have contributed to the notion that long, thin objects could be seen from space. The Ripley's Believe it or not strip from 1932 also makes reference to the Great Wall's visibility from space.
The idea that the Great Wall can be seen from the moon has been refuted numerous times (the Great Wall's apparent width from the moon is equivalent to the width of a human hair when viewed from a distance of 3 km/2 mi), but the idea persists in popular culture.Whether the Wall can be seen from low Earth orbit—as low as 160 km (100 mi)—is a more contentious question. NASA asserts that it is no more noticeable than many other man-made objects, and that it is only really visible in almost ideal circumstances.
"The Great Wall of China is, indeed, visible to the naked eye at Earth orbit of 100 to 200 miles [160 to 320 km] high," said veteran American astronaut Gene Cernan. It's less visible than a lot of other objects, says Ed Lu, the International Space Station's Expedition 7 Science Officer. Furthermore, you must know where to look."
Chinese astronaut Yang Liwei claimed in October 2003 that he had failed to see the Great Wall of China. The European Space Agency (ESA) responded by announcing in a press release that from an orbit ranging from 160 to 320 km (100 and 200 mi), one can see the Great Wall with the unaided eye.
Chinese-American astronaut Leroy Chiao captured this image of the wall from the International Space Station. The photographer was unsure if he had really caught it because it was so faint. The Great Wall can be seen from "space" with the unaided eye under ideal viewing conditions—that is, if one knows exactly where to look—according to a report published in the China Daily based on the photograph.
Features
China's Great Wall during tourist season
The Great Wall was mostly constructed out of rammed earth, stones, and wood before bricks were used. However, during the Ming, bricks and other building materials like stone, tile, and lime were extensively used in many sections of the wall. The bricks were easier to work with because of their weight and size than earth stone.So building accelerated. Bricks could also withstand more weight and last longer than rammed earth. While stone is more difficult to work with, it can support its own weight more effectively than brick. As such, the wall's foundation, inner and outer brims, and gateways were all constructed from stones that had been cut into rectangular shapes. Most of the wall's upper section is lined with battlements, which have defensive gaps that are roughly 23 cm (9.1 in) wide and slightly over 30 cm (12 in) tall. Guards could observe the surrounding area from the parapets. Along the entire length of the Great Wall, army units were able to communicate with one another, call for reinforcements, and alert garrisons to enemy movements,was very significant. For better visibility, signal towers were erected atop hillsides and other prominent locations along the wall. Wooden gates have the potential to be used as a trap for people passing through. In close proximity to the inner wall were constructed armories, stables, and barracks.The Wall is in poor condition in many places, but it has been preserved and even extensively renovated in areas north of Beijing and close to tourist destinations. On occasion, the wall served as a source of stones for constructing homes and roadways. Graffiti and vandalism are also common in some areas of the Wall, and inscriptions on bricks have been stolen and sold for as much as 50 renminbi.Some have been destroyed to make room for mining or building. a 2012 National Cultural Heritage report.According to the administration, 1,961 km (1,219 mi) of the Ming Great Wall have vanished, or 22% of the wall. Due to sandstorm erosion, more than 60 km (37 mi) of Gansu province's wall may vanish over the next 20 years.In certain locations, the wall's height has decreased from over 5 meters (16 feet 5 inches) to under 2 meters (6 feet 7 inches). Many of the square lookout towers that are depicted in the most well-known pictures of the wall have vanished. Since mud was used to build many of the wall's western sections rather than brick and stone, they are more prone to erosion. 2014 saw the concrete repair of a section of the wall close to the Liaoning and Hebei provincial borders. The piece has received a lot of criticism.