Can you really see the Great Wall with the naked eye in space? And is it the only human building that can be seen with the naked eye?

Scientists in China confirmed that "the Great Wall cannot be seen with naked eyes from space". Here are the answers:

CCTV international 2004 12 08 14:53

Xinhua News Agency, Beijing1February 8 (Reporter Li Bin, Bu Yuntong, Wu Jingjing) Can humans see the Great Wall from space? People have been arguing about this for a long time. A recent empirical study by scientists in China has put an end to this historical mystery: through theoretical analysis, remote sensing experiments and field verification, scientists have confirmed that humans can't see the Great Wall with naked eyes from space, but they can "see" it by relying on high-resolution remote sensing technology. Scientists' articles will soon be published in the core journal Physics.

The Great Wall of Wan Li is the symbol and pride of the Chinese nation. From the saying that foreign astronauts "saw" the Great Wall to writing it in primary school textbooks, from Yang Liwei, China's first astronaut, claiming that he had never seen the Great Wall to the recent incident of "seeing the Great Wall from space" created by the European Space Agency, there are many fogs and heated debates.

The European Space Agency's "Seeing the Great Wall from Space" incident in May this year aroused the strong desire of China scientists to find out. Dai Changda, a researcher who has been engaged in remote sensing image interpretation for more than 40 years, has carried out theoretical analysis, remote sensing experiments and field verification with the strong support of Nie Yuxin, an expert in optical physics.

According to the principle of human vision and visual discrimination, several scientists believe that even if the Great Wall is 10 meters wide, the farthest distance for ordinary people to identify the Great Wall is only about 36 kilometers, and scouts with good vision can identify the Great Wall at about 62 kilometers. "These distances are far below the recognized height of space. The Great Wall is generally only 5 meters wide?"

In response to the similar saying of "lighting at night", Dai Changda believes that the Great Wall is a brick-soil structure, not a luminous body or a strong reflector. The contrast with the surrounding background will not be too great, the width and height will be limited, and there will not be too much shadow and projection. "Astronauts may be able to see the Great Wall at the moment of liftoff or landing, but this moment is too short for astronauts to be distracted and impossible to see clearly."

After analyzing the satellite images released by the European Space Agency in May, experts believe that the images have not been accurately geometrically corrected and processed by other applications, which makes it difficult to distinguish the Great Wall images. "The Great Wall recognized by ESA is actually a ravine, and the Grand Canal is the main tributary of Miyun Reservoir-Baihe."

In the absence of ESA satellite image data, scientists applied and interpreted the image of the same area provided by the French "Spot" satellite, and drove to the site for verification. The conclusion is that after proper processing, the remote sensing image with a spatial resolution of about 5 meters can clearly show the existence of the Great Wall. (End)

The Origin of the Mystery of History —— A Memorable Debate on "Seeing the Great Wall with the Naked Eye from Space"

It seems that the origin of this scientific case can be traced back to the day when humans first entered space, and the words of astronauts "seeing the Great Wall" immediately spread all over the world. At this point, it has taken root in people's hearts, especially hundreds of millions of Chinese children.

Since then, the debate about human beings seeing the Great Wall with naked eyes has never been broken, and it has also been divided into two camps in the aerospace, scientific and even public circles: one group thinks that the Great Wall can be seen with naked eyes from space; One school thinks this is impossible. The pros and cons, like a debate, each moved out of the scientific basis and made sense. For the vast majority of the uninformed or undiscovered public, it is like looking at flowers in the fog, and a scientific case seems to have become a historical mystery.

Let's sort out the "great events" surrounding this mystery in recent years-

William Borg, an astronaut who once worked in the space station, said in his book How to Bath in Space published in 199 1 that it is impossible to see the Great Wall with naked eyes at that height, but you need a telescope to see it.

In 2000, Phoenix TV interviewed Aldrin, one of the first astronauts to land on the moon. He said that the Great Wall of Wan Li could not be seen on the moon. The Great Wall is narrow and irregular, so it is difficult to see irregular things on the track.

On May 4th, 2000, Tito, the first space tourist, also said in an interview that when I was flying over China, I saw the rivers and mountains of China, but I didn't see the Great Wall of China.

Yang Liwei, China's first astronaut, said after returning to the earth in 2003 10: "It's very beautiful to see the scenery of the earth, but I didn't see our Great Wall."

At the beginning of 2004, Wang Xiang, a member of the Chinese People's Political Consultative Conference, put forward a proposal at the Second Session of the Tenth Chinese People's Political Consultative Conference, asking the relevant departments to correct the mistakes in the text "Bricks of the Great Wall" in the seventh volume of primary school Chinese as soon as possible. The Ministry of Education publicly replied that rectification work was under way.

Eugene cernan, an American astronaut, said during his visit to Singapore in February, 2004 that "the Great Wall of China can indeed be seen with naked eyes in the earth orbit160-320km high". Ed Liu Ye, the scientific officer of the International Space Station Expedition 7, agrees with him.

On May 1 1, 2004, a high-resolution satellite image of the Great Wall of China, which was taken from space, was published on the homepage of the website of the European Space Agency. The image was obtained during the transit of satellite Proba on March 25th. The caption points out that a thin winding line in the upper right corner of the picture is the Great Wall stretching for 7240 kilometers. The announcement also believes that astronauts can see the Great Wall with the naked eye if the weather, lighting and other conditions are suitable.

Only one day after the announcement, NASA's website forwarded this information and picture. The information released by two internationally recognized space science and technology authorities immediately attracted widespread attention. A report like "Seeing the Great Wall from space is not a myth" appeared in many domestic media, and an article "stopped" the proposal that CPPCC members suggested that primary school Chinese textbooks should be revised.

At the same time, doubts and negative opinions also appeared in newspapers and websites. Scholars from Fudan University and the University of California first proposed that it could not be the Great Wall. According to the stereoscopic effect and the rotation of 180 degrees, the image is obviously a ravine with water gathering.

On May 19, 2004, ESA issued an error correction notice, admitting that there was an interpretation error in the previously published image, and misjudged a river injected into Miyun Reservoir as the Great Wall. As for whether the image judged as the canal is wrong or not, whether the astronauts can see the Great Wall is not mentioned.

On May 27th, 2004, the scientific and technical personnel of Beijing Institute of Surveying and Mapping put forward a new viewpoint after superimposing and analyzing aerial photos, 1: 10000 topographic map and ESA image. The Great Wall is not a river, it's a mountain road.

On June 4, 2004, it was suggested that "Yang Liwei didn't see the Great Wall for a reason": Yang Liwei didn't fly over the Great Wall in the 2 1 hour space flight, so he didn't have time to see it at all.

In May, 2004, tereshkova, a female astronaut from the former Soviet Union, revealed during her visit to China that she had seen the Great Wall in the course of 1963 circling the earth 48 times. (Xinhua News Agency reporters Li Bin, Wu Jingjing, Bu Yuntong)