The Great Wall of China can be Seen from Space

Abstract

Whether the Great Wall of China is visible from space by naked eye has become a space-based myth. Conflicting stories told by astronauts have been reported in various media. Several scholars also tried to give a much needed scientific answer to the question through their own research. Recently, Chinese scholars Dai et al. published their analysis based on visual acuity of point objects and concluded that astronauts cannot see the Great Wall of China from space. However, our analysis based on the human's visual acuity of linear objects concludes that the Great Wall can be seen at the altitude up to about 500 km. Some environment conditions on the ground may dampen the chance of a successful observation.