It has been almost 40 years since the first human walked on the surface of the Moon - and for nearly as long conspiracy theorists have called it a hoax.
Far from science fiction
By now only the most wide-eyed space cadet could avoid feeling a bit jaded by the seemingly endless celebrations of the first moon landing, which took place exactly 40 years ago tomorrow. Just how much more is there to say about the Apollo 11 mission of July 1969, which resulted in Neil Armstrong and Buzz Aldrin becoming the first humans to visit another celestial object? For one group of people, the fuss is especially irksome. They are the conspiracy theorists who for decades have insisted that Armstrong's historic "giant leap for mankind" took place rather closer to home. In books, videos and television documentaries, they have claimed to have compelling evidence that the mission was a hoax.
Just how big a hoax depends on whom you ask: some hardliners even claim that the lift-off of the Saturn V rocket was faked, and that all those thousands of spectators and news reporters who supposedly attended the launch from Cape Kennedy were in on the conspiracy. Most, however, draw the line at the admittedly astonishing events that took place a few days later, claiming that the moonwalk was actually filmed in a film studio.
Much of the supposed evidence comes from anomalies in the film and photographs taken on the Moon. For example, some of the images show shadows spreading apart as they disappear into the distance - as if the scene were lit using studio lights rather than the Sun. Then there is the absence of stars in the lunar sky, again pointing to a studio mock-up. In fact, both these "anomalies" have perfectly good explanations. Non-parallel shadows are a perspective effect, especially noticeable even on Earth when the Sun is low in the sky - as it was during the Apollo missions. As for the absence of stars, this is simply the result of the astronauts' camera exposures being set for bright objects rather than faint ones.
Why would Nasa want to fake the lunar landings in any case? Some conspiracy theorists claim it was simply a financial scam, allowing the agency to pocket billions of dollars from gullible taxpayers. But most focus on the dangers of space travel, in particular the risk from solar radiation. They have a point. Once outside the Earth's protective magnetic field, astronauts are vulnerable to fast-moving particles blasted out by the Sun, which could cause radiation damage to their cells.
Most of the time, the level of radiation is too low to cause significant harm over a roughly week-long mission to the moon. Proof of this came a year before the flight of Apollo 11, in one of the unsung triumphs of the Soviet space programme. In September 1968, the Zond 5 probe took a "crew" of two tortoises, plus various bacteria, flies and worms, within 2,000km of the lunar surface. While overshadowed by the triumph of the first manned circumnavigation of the Moon by Apollo 8 a few months later, the Zond 5 mission was the first-ever round trip to the Moon by living creatures, and confirmed that the journey did not pose an obvious threat to life. Even so, every so often the Sun experiences magnetic storms that produce huge surges in space radiation. With weight restrictions preventing any radiation shields being installed on Apollo, the astronauts were undoubtedly at some risk from solar flares. And last month, Nasa admitted that only luck had prevented a catastrophe with its moon missions.
On August 2, 1972, the Sun unleashed a record-breaking torrent of fast-moving protons. Fortunately, the eruption took place during the gap between Apollo 16 and 17 missions, so no astronauts were exposed to the resulting blast of radiation that flashed through space. This highlights something largely glossed over by the celebrations of the moon landings: there were some very close calls which almost resulted in disaster.
Arguably the scariest took place during Apollo 11's historic final descent to the Moon. Under computer control, the lunar module swept down to the planned landing site: a nice, flat part of the Sea of Tranquillity. Yet on their final approach, Mr Armstrong and Mr Aldrin could see they were heading straight for a crater strewn with boulders. Seizing control, Mr Armstrong halted the descent and began a desperate search for somewhere more suitable.
Even his vast experience as a test pilot could not prevent the stress doubling his heart rate to over 150. And small wonder: he was rapidly running out of time, as the famous recording of the final descent reveals. Mission Control Center in Houston can be heard breaking in with "60 seconds", followed by Aldrin saying "Light's on" - meaning the low fuel warning indicator was lit. Mr Armstrong was still looking when mission control broke in again with "30 seconds". Finally spotting a suitable site, he brought the module in for a soft landing. But in the stress of the moment, he forgot to switch off the engine, risking a dangerous blowback up into the spacecraft. Flicking the "Engine Stop" switch, the module finally landed. Small wonder there were "a bunch of guys about to turn blue" back at mission control.
Fortunately, the rest of the mission went smoothly. Armstrong and Aldrin collected some lunar rock, and then rejoined Michael Collins in lunar orbit for the long journey back to the Earth. Only after they returned did it become clear that mission planners had committed a huge blunder - and one no hoaxer would have dreamt of making. They had given Mr Armstrong the role of chief photographer, and as a result there are virtually no images of him on the lunar surface. All the best-known are of Aldrin, the second man on the moon.
As the saying goes, you couldn't make it up. Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England