A research team at the Chinese Academy of Sciences recently completed a study into whether it is possible to see the Great Wall with the naked eye from space, a belief that was recently challenged by Chinese astronauts. They have confirmed that the Great Wall is only visible using a remote satellite sensing device that has a certain spatial resolution.
According to China News Agency, a research team from the Academy of OPTO-Electronics under CAS led by Dai Changda and including Jiang Xiaoguang and Xi Xiaohuan, has completed a joint research project, publishing their findings in the latest issue of the "Science and Technology Review". They have found that human vision starts in light and color perception and ends in shape perception, which relates to the size and distance of the objects. The angular magnitude of the pupils of the eyes is equivalent to only 1/3,600 of the circumference. Accordingly, even when visibility is good, ordinary people can only perceive shapes larger than 10 meters at a maximum distance of 36 kilometers away. This is much lower than the distance it is generally acknowledged at which space begins �C 10 kilometers. The Great Wall is only two meters in width. Except for large frontier passes, most beacon towers are only five to six meters in width. Therefore, it can be concluded that it is indeed impossible for astronauts to see the Great Wall with the naked eye from space.
The three Chinese astronauts who successfully visited space have confirmed that they could not see the Great Wall.
By People's Daily Online