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On Monday a senior Chinese cultural heritage official expressed the hope that the country's astronauts could prove whether the Great Wall can be seen with the naked eye from space during their next mission.

Answering questions of netizens online at www.gov.cn, the government website, Tong Mingkang, vice director of the State Administration of Cultural Heritage said, "There's still no definite evidence to prove whether the Great Wall is visible from space.

"Many people including foreigners are interested in this question. The curator of the national museum of Egypt asked me the question recently," said Tong.

But it was really difficult to answer the poser because only a few astronauts have ever been to space, Tong said. "We hope Chinese astronauts may prove that during the next space mission," he commented. 

During China's initial manned space flight in 2003, Yang Liwei, China's first astronaut said he didn't see the Great Wall while in orbit and contradicted the popular belief that the structure was visible from space.

This later triggered a hot debate in China over whether a school textbook teaching that the Great Wall could be seen from space should be corrected.

Adding another twist, veteran U.S. astronaut Gene Cernan insisted the Great Wall could be seen. Cernan, the last man to walk on the moon as commander of the Apollo 17 mission, said he had seen the Great Wall from the Earth's orbit although he couldn't do so while on the moon.

"In Earth's orbit at a height of 160 to 320 km the Great Wall of China is indeed visible to the naked eye," he was quoted as saying during an interview by a Singapore newspaper in March of 2004.

It's widely accepted that in the Earth's orbit, which is normally 300 to 400 km from the ground, only an object larger than 500 X 500 meters can be seen with the naked eye. The Great Wall, which is made up of sections approximately 10 meters wide, should be invisible from outer space scientists believe.

According to a report in China Daily on April 19, 2005, Chinese-American astronaut Leroy Chiao, who'd been on three space flights and was coming to the end of his six-month stint on the joint U.S.-Russian space station, provided the first photographic evidence of sections of the Great Wall using commercially available equipment.

The photos had been authenticated by Professor Wei Chengjie of the Institute of Remote Sensing Applications at the Chinese Academy of Sciences, the newspaper said.

However, Chiao was himself not certain. "It's hard to say whether or not I have seen it. That's because from our altitude I can't distinguish between the Wall and roads." He described his picture, taken on February 20, 2005 as a "region northwest of Beijing."

Work on the Great Wall started in the time of the Qin Dynasty (221 BC -206 BC) as a way to defend against invaders from the north. It was extended and rebuilt intermittently over the centuries.

The majority of the existing Great Wall winding west-to-east from the Jiayu Gate to the Yalu River in north China was built and rebuilt in the Ming Dynasty (1368-1644). It was included in the World Heritage List in 1987.

(Xinhua News Agency October 31, 2006)