US astronauts who claim to have spotted the Great Wall of China from space must be imagining things, Chinese scientists say. The Great Wall of China cannot be seen from space, because the human eye cannot resolve such fine detail, a team of academics stated in a recently published paper.
At least two US astronauts say they spotted the Great Wall from earth orbit – above 150km. They include last man on the moon, Gene Cernan; and international space station crewmember Ed Lu.
Another US astronaut, Leroy Chiao even snapped a photo of the wall with his own camera, as he orbited the earth at 348km.
But the researchers from the Chinese Academy of Scientists claim the greatest height the 10 meter-wide wall could be seen from is about 36km – in perfect weather. The team, led by satellite optics expert, Professor Dai Changda, published an article in China's Science & Technology Review refuting the US claims.
Researcher Jiang Xiaoguang had little time for US astronaut Chiao's photographic evidence. "Obviously, the human eye is quite different from a camera. It can't detect details that advanced photographic equipment can,” Jiang told a reporter from the state-sponsored Xinhua news agency.
Chiao himself earlier admitted that he had not been able to see the wall when he took the photos. He used a 6 megapixel Kodak camera with a 180mm lens.
For decades, Chinese school textbooks have taught that the Great Wall is the only man-made object visible from space. Many Chinese took great pride in this, and were surprised and disappointed when China's first astronaut, Yang Liwei, reported in 2003 that it could not be seen.
However, the following year, US astronaut Chiao's orbital photographs of the wall were published in Chinese newspapers to what NASA reports described as “relief and rejoicing by the Chinese”.
According to NASA, the wall may become much easier to spot from space under certain conditions. For example, the 10m-wide wall can cast a much wider shadow when the light angle is low. And during winter months, snow piled against the wall, which is in Northern China, might highlight it.
However, having long backed claims that the wall is visible from orbit, China's academic establishment – or at least some members of it – now seem bent on proving that it is not.