Washington, July 16 (DPA) Even conspiracy theories must sometimes be taken seriously.

Every week Roger Launius, chief historian at the Smithsonian National Air and Space Museum in Washington, devotes his time to debunking one of history's favourite such theories: That astronauts Neil Armstrong and Buzz Aldrin never landed on the moon.

The entire July 20, 1969, landing and the spacewalk several hours later was just a show, all lies, filmed in a Hollywood studio or in a desert, the sceptics say.

Few other conspiracy theories have proven so popular or long-lived.

'We Americans love that sort of thing,' Launius said as he stood before a lunar lander like the Eagle that took Armstrong and Aldrin to the moon's surface.

In fact, conspiracy theories abound in the US: the Sep 11, 2001, terrorist attacks were planned by the government; President Barack Obama is not really a US citizen; and various false hypotheses about the assassination of president John F. Kennedy.

It didn't take long after the moon landing for wild speculation to surface. Then the 1976 book, 'We Never Went to the Moon - America's 30 Billion Dollar Swindle', by Bill Kaysing really got things going. It was the era of Watergate and the Vietnam War, and the theories played off the resulting distrust of the government.

At one time, up to 10 percent of Americans may have believed the conspiracy theories about the moon. On average, it has dropped to about six percent of Americans, Launius said.

The arguments of the critics include the 'waving flag', the 'missing stars' and 'false shadows' in television images. But at the root of the idea is that the country was not yet technologically advanced enough to make the trip.