Civilians cannot get close to Area 51 and commercial airliners are not allowed over it. No US President has ever seen it. Now, however, anybody can peer into the sprawling and spookily mysterious military installation deep in the Nevada desert - thanks to one satellite and the internet.
What was invisible for decades has been unveiled in photographs now posted on the world wide web by a private firm in North Carolina. Five pictures taken by a Russian-built satellite offer views of Area 51 that are so well defined you can tell a bus from a van and a van from a car.
But as soon at the pictures were coming up on the Web yesterday, the site that carried them - www.terraserver.com - inexplicably crashed. Was this sabotage by the government? Not according to Aerial Images of North Carolina. Rather the site had at first been inundated by surfers and then brought down by hackers. "It is being hammered," said the company's president, John Hoffman.
For those who do find them, the pictures confirm what the Pentagon for years could never bring itself to acknowledge: that in the Nellis Range, 75 miles north-west of Las Vegas, there is, indeed, a government installation. The base covers an estimated 8,000 square miles beside Groom Lake. Look at the satellite images and you can see runways and roads and even one aircraft. (Though it is hidden under a camouflage drape.)
There is more. Unpaved tracks lead into the desert and stop at cliff faces, implying additional facilities underground. The site includes a baseball diamond, a swimming pool, hundreds of nondescript buildings and tennis courts and lots of small craters, apparently made by objects falling from the sky.
No amount of squinting, however, will reveal either green men or anything resembling a flying saucer. This will disappoint UFO enthusiasts and conspiracy theorists, who contend that much more happens at Area 51 than ordinary air force business. Equally, however, it is hardly likely that these pictures will dispel all the myths that have swirled around the base for so long.
Foremost among these is the notion that the real reason for Area 51 to exist - and for the obsessive secrecy that surrounds it - is that this is where the US government hides whatever evidence it has of the existence of alien civilisations. That would include parts of alien craft that have landed on Earth and, especially, the remains of the ship that ufologists still believe crashed at Roswell, New Mexico, in 1947.
The inter-planetary legends of Area 51 have been further popularised recently by the phenomenally popular The X-Files television show, to which UFOs and clandestine government activities are central themes. The show's mantra runs: "The truth is out there."
Aerial Images is the company behind the satellite snaps. "This is the first glimpse into the most secret training and testing facility for the Air Force," Mr Hoffman said. He first posted the pictures on the internet late on Monday in collaboration with Microsoft, Kodak, DEC, Autometric and a Russian agency, Sovinformsputnik.
The project began when these six partners launched a Russian satellite from Kazakhstan in 1998. The mission was to map the surface of Earth. Taking pictures of Area 51 and publishing them is not illegal thanks to the 1992 "open skies" treaty that allows all 24 signatory nations to photograph each others' territories to witness progress towards disarmament.
The US government seemed sanguine about the release of the satellite pictures, but it has always dismissed the extraterrestrial rumours about Area 51 as nonsense, and has sometimes gone to great lengths to dispel them. for example, it released photographs of a crashed Viking spacecraft three years ago to show how easy it would be to mistake the wreckage of a man-made craft for an Alien spaceship.
As for Area 51 - the name was taken by conspiracy theorists from old test-site maps of Nevada - the Pentagon no longer denies its existence outright. The official line is that it is "the air force's operation location near Groom Lake, Nevada". A Pentagon spokeswoman, responded tersely yesterday to the release of the satellite images. "We acknowledge having an operating site there, and the work is classified," she said, adding that the work involves "operations critical to the US military and the country's security".
Back in the 1950s, Area 51 served as a secret base for test ing the U-2 spy plane. And since then, it is believed to have been the main testing ground for successive top-secret aircraft, including the SR-71 Blackbird and, more recently, the F-117A stealth fighter and the B-2 stealth bomber. Rumours persist about a programme at the site to develop a hyper-sonic aircraft dubbed "Aurora". The plane, said to be the fastest machine ever made by man, can allegedly fly at 1,270mph.
The nearest community to the southern edge of the base is Rachel. For two decades, it has been a shrine for UFO believers coming to watch the night sky for those green flashes and spinning saucers. The town's only hotel is called the A'le'Inn - a play on alien. Its sign reads "Earthlings Welcome".
Jonathan Turley, director of the Environmental Crimes Project at George Washington University, has campaigned for the demystification of Area 51. He has filed lawsuits against the US government on behalf of former employees at Area 51 who claim to have been poisoned by toxins there.
"I've long felt that the military has been delighted with the circus environment over aliens at Area 51 because it's not only a welcome distraction, but it make our entire litigation look ridiculous by association," Mr Turley said recently.
Mr Hoffman, meanwhile, said he had contacted the creator of The X-Files, Chris Carter, to tell him of the images. The reaction was incredulity. "He clearly did not believe me," Mr Hoffman joked. "From his tone, you could tell he didn't believe me that we had Area 51 and we had the whole area covered".
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