SINGAPORE: Now you see the Great Wall of China. Now you don't. Or perhaps the landscape is to blame. Or else someone is lying. Whatever the answer, the visibility - or lack thereof - of the thousands-of-miles-long monument from space is threatening to become an international incident after the last person to walk on the moon has reportedly insisted the structure is visible to the naked eye.

This contradicts China's first astronaut, Yang Liwei, who last week was quoted as saying the complete opposite - prompting the education ministry to order the rewriting of elementary school textbooks.

Gene Cernan, who turned 70 on Sunday, allegedly told Singapore's Straits Times in an interview published on Sunday: "At Earth orbit of 160km to 320km high, the Great Wall of China is indeed visible to the naked eye."

Mr Cernan, who has logged more than 556 hours in space, claimed it is all a matter of knowing where to look. "If you know where to look and you look hard enough, you can also see the Astrodome in Houston, Texas, where I live," the report quoted him as saying.

On Friday the Beijing Times said that Colonel Yang, who spent 21.5 hours in space last year, said he could not see the wall, which is only a few metres wide.

It quoted an education ministry official as saying the publisher of the textbook that includes the "falsehood" had been told to stop printing the essay in question. "Having this falsehood printed in our elementary school textbooks is probably the main cause of the misconception being so widely spread," the paper said.

The US officially appears to side with the Chinese. Janice Voss, who flew on the space shuttle last year, says on the website of the government's space agency, Nasa: "You can't see it with the naked eye in any way. But ... with a 200-millimetre lens on a camera you can pick it out." -Dawn/The Guardian News Service.