Original Moonwalker: How Neil Armstrong kept his feet on the ground despite becoming the most famous man on Earth

Forty years on, the debate is over. He didn't say the "a". Neil Armstrong meant to, of course; the line he had prepared to mark the climax of humankind's greatest adventure of the 20th century should have come out as "One small step for a man, one giant leap for mankind". But the "a" somehow got lost. Some experts blamed it on his flat Midwestern accent. Some maintained the humble indefinite article was obliterated by static.

But a phalanx of phoneticians and speech analysts have gone over newly enhanced magnetic tapes of those imperishable words from the Sea of Tranquillity, and in May they announced their finding. There was not room – not even the 35 milliseconds posited by Australian researchers in 2006 – for an "a", whether half swallowed, elided or otherwise consumed. Armstrong simply didn't say it. Either he forgot, or for once nerves got to this most nerveless of men.

If Armstrong had his way, this scientific debate about the missing "a" would be the only point of interest this upcoming 20 July, and he would continue to live the quiet and anonymous life has has built for himself, without interruption. But, for a few weeks at least, it cannot be. That day in 1969, a global television audience of 500 million watched this quiet son of an Ohio state auditor become the first man to set foot on the Moon.

The TV images, in truth more snow than picture, may now be museum pieces. But they remain as thrilling and incredible as when they appeared for the first time, generating an unchanged sense of miracle. The technology was primitive: a tiny modern cellphone packs vastly more power than the Doctor Who-like electronics that graced Apollo 11, all toggles and blinking lights. Yet these clunky instruments somehow guided Armstrong and fellow astronaut Buzz Aldrin to an alien world – even if the onboard computer effectively crashed because of data overload even as the lunar module started its descent.

There was another scary moment in the last instants before the landing, as Armstrong had to steer the craft away from some boulders, consuming extra seconds of vital fuel in the process – and yet another when they prepared to depart and the engine ignition switch for lift-off had broken. They solved that mini-crisis by using a pen to break a circuit and activate the launch process.

In the end, the mission went well-nigh perfectly. The men from Apollo 11 might have spent only two and a half hours outside the lunar module, and less than a day in all on the Moon's surface. But in that short space of time Armstrong had joined – some would say even eclipsed – Columbus, Amundsen, Lindbergh and the rest in the pantheon of explorers whose exploits changed history. And, once inside the pantheon, he has surely managed the burden of celebrity as well or better than any of them.

Destiny surely pre-ordained him for the role. He was born here in the flat farmlands of western Ohio, in the state that has produced more astronauts than any other, just 50-odd miles north of Dayton where Orville and Wilbur Wright pioneered the science that would take Apollo to the Moon.

As a boy, Armstrong was fascinated by flight, and by the engineering and physics which made flight possible. At 16, before he had learnt to drive, he was the proud possessor of a pilot's licence. Five years later, he was flying combat missions over Korea, and after that war he became a hotshot test pilot at Edwards Air Force Base in California's Mojave desert, flying the Bell X-1, the hypersonic North American X-15 and other exotic planes chronicled by Tom Wolfe in The Right Stuff, that formed the bridge between the early jet age and the space age.

In one 1962 incident that is now part of Edwards legend, Armstrong messed up an X-15 descent and flew over the base where he was scheduled to land at a speed of Mach 3 (2,000mph) and an altitude of 100,000ft. But he managed to rectify the mistake, turning from above north-eastern Los Angeles back towards Edwards, and executing a high-speed glide to get the plane safely down instants before it would have crashed.

The episode was vintage Armstrong, cool and resourceful, and seemingly without nerves. There would be similar moments later. One came in 1966 during the Gemini 8 flight, Armstrong's first in space, which completed the first ever docking of two vehicles. The Gemini spacecraft suddenly began rolling, uncontrollably and ever faster. On the verge of blacking out, he decided to fire the re-entry rockets, aborting the mission, but probably saving the lives of himself and his fellow pilot David Scott.

In 1968, Armstrong was practising for the Moon trip on the LLTV, the Lunar Landing Training Vehicle better known as the "Flying Bedstead", when the craft began to fly out of control at an altitude of just 100ft. In the nick of time he ejected, a second or so before the LLTV smashed into the ground in flames. In typical unflappable fashion, he brushed himself down and went back to his office to do some paperwork.

It was mostly luck that Armstrong was on the Apollo 11 mission, his second actual space flight. An accident or a technical glitch might have altered the timetable; another crew might have found itself heading to the Moon. But it was perhaps less accidental that Armstrong was selected to be commander, and then designated to be first out on to the lunar surface.

The man himself insists not. "I wasn't chosen to be first. I was just chosen to command that flight. Circumstance put me in that particular role. That wasn't planned by anyone," he maintained in a 2005 interview with CBS television. But was it really a fluke of fate? Perhaps some shrewd individual at Nasa realised that the Moon landing carried with it more than every man's standard 15 minutes. Armstrong, this wise man may have concluded, would be better able to cope with the lifetime of celebrity ahead than, say, Aldrin – who after his space days lapsed into depression and alcoholism and still attends rehab, and whose latest venture, confided to a New York Times interviewer last month, was a rap session with Snoop Dogg?

And incontestably, 20 July 1969 changed Armstrong's life for ever. In his professional circle, "friends and colleagues all of a sudden looked at us, treated us slightly differently than they had months or years before when we were working together. I never quite understood that," Armstrong would tell James Hansen, author of the 2005 biography First Man: A Life of Neil A Armstrong.

For a person instinctively averse to publicity, even worse was to come. The success of the Moon mission turned Armstrong, Aldrin and Michael Collins – who flew the orbiting command module – into global heroes and champions of brand America. They were the men who had definitively bested the Soviet Union in the greatest peaceful struggle of the Cold War. First came a ticker tape parade in New York before a crowd of four million, then a 45-day "Giant Leap" tour around the world, when the three were feted by royalty and heads of state.

Armstrong could have succumbed to the adulation, using celebrity as springboard for a new career. He could have gone into politics, like his colleagues John Glenn – who represented Ohio for 24 years in the US Senate – and Harrison "Jack" Schmitt who served a term as senator for New Mexico. He could have become a professional pitchman, an ambassador for Nasa, a television talking head.

He could have cashed in on the lecture circuit with speeches for tens of thousands of dollars a time. Or, of course, he might have gone off the rails like Aldrin, who has recounted his experiences in a memoir, Magnificent Desolation: The Long Journey Home from the Moon, timed to coincide with the 40th anniversary. Among mind-changing experiences, few can rank higher than walking on the Moon, an experience granted to just 12 men, of them only nine still alive.

But Neil Armstrong was different. His priority was a normal life. For him, two years as Nasa's show pony were more than enough. In the summer of 1971 he went back to his early passion of aeronautical engineering, taking a professorship at the University of Cincinnati. A predictable and mighty flurry of media attention soon subsided after Armstrong made clear he was there to teach, not talk to the press.

To aide the transition, Armstrong made a careful study of what had happened to Charles Lindbergh. By the time of the Moon flight, the man who had made the first solo transatlantic flight was in his 70s. But his 1927 exploit had turned him into the most famous man in the world, and changed his life for ever – and not for the better.

The similarities with Armstrong were considerable. In their respective heydays, both were young and handsome heroes. In later years Armstrong might have gained a certain portliness; but in his prime in the 1950s and 1960s he was every inch a top gun of his day. Both men too were shy and reserved, and their politics leant to the right, based on a belief that America should stay out of foreign conflicts.

And, finally, each had known family tragedy. Back in 1932, the kidnapping and murder of the Lindbergh baby – probably the most sensational and avidly covered criminal case in US history – had banished for ever the moniker of "Lucky Lindy". In 1962, Armstrong experienced the grief of losing his two-year-old daughter Karen to brain cancer.

That the two pioneers, though 28 years apart in age, should feel an affinity and strike up an acquaintance was inevitable. "I wonder," Lindbergh wrote to Armstrong after the landing, "if you felt on the Moon's surface as I did after landing at Paris in 1927: that I would like to have had more chance to look around."

Even more revealing was Lindbergh's reaction to an invitation to fly out with President Richard Nixon to personally greet the three returning conquerors on the aircraft carrier USS Hornet – albeit only through a glass window into the trailer where Armstrong, Aldrin and Collins were being held in quarantine for three weeks, lest they had brought back some lethal lunar bug.

Lindbergh turned his president down. The decision, he later wrote, was based on what happened after his own historic flight, "when I spent close to a quarter century re-achieving a position in which I could live, work and travel under normal circumstances". The Moon landing and its follow-up, the old aviator feared, "would attract the greatest concentration of publicity in the history if the world," and he himself would be forced back "into a press relationship and way of life I am most anxious not to re-enter."

Neil Armstrong took those words to heart. Since his departure from Nasa, his career has been a case study of how to live with extreme celebrity – and proof that a dislike of the limelight, a somewhat solitary nature, and a reluctance to speak to the press do not mean that a man has turned into a recluse or hermit. Indeed, it was a string of appearances after the outbreak of war in Europe in which Lindbergh urged America to strike a neutrality pact with Germany and seemed to criticise the Jews that created such controversy for the aviator. Armstrong never ventured onto comparably treacherous public terrain.

"Fame never turned his head; he's a true professional," says John Swez, an old family friend. "Buzz Aldrin may have lost it a bit, but not Neil. He's certainly not reclusive. He's got a good sense of humour. The first time I chatted with him at length, he was funny and outgoing. He's probably the most intelligent man I've ever talked to. Yes, he's careful in what he says, but I think it comes from that level of intelligence. He wants to get it right."

Above all Armstrong sought normality. Unlike several of his colleagues, he never wrote his memoirs. It was only after some misgiving, and more than three decades after the Apollo 11 flight, that he agreed to co-operate with Hansen, an eminent historian. The 750-page authorized biography is dense and scholarly, crammed with fascinating detail, but as unflamboyant as its subject.

At the end of 1979, Armstrong left Cincinnati University, and thereafter served on a few corporate boards. A rare public venture was an advertisement that same year for Chrysler, aired in the Super Bowl. The spot, in which he praised the company's engineering, was poorly reviewed. But Armstrong's personal credibility might have helped the car manufacturer, under its charismatic then chairman Lee Iacocca, survive a first brush with bankruptcy.

The Moon walk has left its mark on Wapakoneta, an unpretentious town of 9,400 souls, whose main monument is one of those domed and foursquare county courthouses, built in the late 19th century, that are scattered over the Midwest. The Armstrong family moved away soon after Neil was born but returned in 1944 for three years.

The astronaut's old high school, where he excelled in science and achieved the top Eagle rank in the Boy Scouts, is now a residential building. But the family's two-storey clapboard house at 601 West Benton Street looks much as it must have done then, neat and smartly painted in grey and white. Once there was a plaque reading "Eagle's Landing, boyhood home of Neil Armstrong, first man to walk on the Moon", but it was blown away in a storm a few years ago. The neighbourhood, however, still evokes an America of the 1940s and 1950s, of old fashioned small-town values, when people had their heads screwed on right, and no one got carried away.

Except of course in 1969 they were. "Neil steps on the Moon" was the banner headline on the front page of the Wapakoneta Daily News of 21 July 1969. It might have been one of those "Aliens land in Ohio garden" scoops that were once the speciality of the now defunct Weekly World News. But this was no supermarket tabloid fantasy. This story was true.

The Neil in question was the bright kid who graduated from Blume High School, and in Wapakoneta today you can scarcely drive a block without a without a reminder of his feat – the Moon florists, the Apollo Storage Company, not to mention the framed front page from The New York Times of 21 July 1969 that greets a visitor to the men's room in the McDonald's on the way into town, off Interstate 75.

In his home town, Armstrong's reserve is not universally appreciated. Some would like to see a bit more of the local boy made supremely good, of whom they are so inordinately proud. His declining of an invitation to take part in local festivities celebrating the 25th anniversary of the Moon landing in 1994 was particularly upsetting. Others argue that America should have had a more visible front man for the most beguiling high tech feat in its history.

Armstrong however has explained his modesty thus: "I guess we all like to be recognized not for one piece of fireworks, but for the ledger of our daily work." Lindbergh's flight was very much a solo affair; he by contrast was the beneficiary of a giant decade-long Nasa operation that in one way or another had involved over 300,000 people. So why, asks Armstrong, should he receive all the glory? "I just don't deserve it." And you can make the case that, in this post-Bush era, modesty, caution and a willingness to think before speaking are exactly what America's global image requires.

But the Armstrong style can be disconcerting. "The first occasions I spoke to him, he would take his time before responding," says Rebecca Macwhinney, manager of Wapakoneta's Armstrong Air and Space Museum. "But when he answered it was in a very articulate fashion, with perfectly formed sentences. What comes across is that he's a very intelligent man."

She was not the first to have that experience. In The Right Stuff, Wolfe writes of Armstrong that "you'd ask him a question, and he'd just stare at you with those pale blue eyes of his, and you'd ask the question again, figuring he'd not understood and – click – out of his mouth would come forth a sequence of long, quiet precisely thought-out sentences.... It was as if his hesitations were just data punch intervals for his computer."

Then, as now, Armstrong was a man totally in control. Today he makes the odd public appearance but mainly lives quietly with his second wife Carol at the 200-acre farm he bought in 1971 in Lebanon, Ohio, a half hour drive north of Cincinnati. In true Armstrong fashion, his 1994 divorce from Janet, his first wife of 38 years, passed by almost unnoticed.

The corporate directorships have enabled him to live comfortably but not extravagantly. Beyond that, he has never exploited his fame. He has donated many personal items to the museum named after him, and which teems with visitors, but rarely visits the place himself – and on the occasions he does, always unannounced. His greatest regret is that he did not spend more time with his family, especially when his two sons were growing up. When his infant daughter died, Armstrong's response was to throw himself even more fully into his work.

Having gained little from his name, he detests it when others try to do so for themselves. "It happens all the time, Swez remembers. "Once someone called up saying he had a relative dying of cancer, and could be have a picture autographed. We checked it out and the whole thing was a lie." In 1994 he sued Hallmark Cards after it used the "one small step" quote in a Christmas item without his permission. Armstrong won the lawsuit, and donated the proceeds to Purdue University in Indiana. A few years ago, Armstrong even threatened to sue his barber of over 20 years in Lebanon, Marx Sizemore, for selling some of his hair for $3,000 to a collector: the matter was settled when Sizemore donated the money to a charity specified by Armstrong. "The one thing he hates is being exploited," says Swez.

But in 1996 Armstrong broke his own no-autograph rule to help restoration work on Wapakoneta court house. The local authority had to find $32,000, and Armstrong agreed to sign 250 prints of the courthouse to raise the money. But, he stipulated, they had to be sold to locals – otherwise dealers would have scooped them up and sold them for thousands of dollars apiece.

As events would have it things lunar quickly lost their lustre after the giddy euphoria of 1969. The last manned landing, by Apollo 17, was in 1972, and the focus of space exploration shifted to manned low orbital shuttle flights and unmanned probes to more distant planets. The Moon seemed less a gateway to the heavens than a cul de sac, and the headlines were consumed by the bleaker earthly dramas like Vietnam and Watergate.

Even so, Armstrong was surprised how quickly the Moon lost its appeal. He knew the Apollo programme could not go on for ever, "but I fully expected that, by the end of the century, we would have achieved substantially more than we actually did," he told CBS in 2005. "When we lost the competition [from the Soviet Union] we lost the public will to continue."

Now, however, as Armstrong prepares to celebrate his 79th birthday this August, the Moon is belatedly making a comeback. In 2004 George W Bush announced plans to send men back to the Moon by the end of the next decade, and Nasa intends to have a solar-powered base up and running, permanently staffed, by 2024, to prepare future human missions to Mars and other planets. This October, the agency plans to send a rocket smashing into the surface of the Moon to create a plume of rocks and debris stretching 150 miles up into space. This in turn will be analysed by a satellite for traces of water ice, crucial for any permanent station. And, back down on Earth, a gentleman farmer in western Ohio will be monitoring proceedings, his fingers crossed, with a quiet smile of satisfaction on his face.

MOON FACTS

* Twelve men have walked on the Moon. All American, their later activities include painting (Alan Bean), looking for Noah's Ark (James Irwin) and getting engaged to news reader Anna Ford (David Scott)

* It took the Apollo 11 team four days to fly the 239,800 miles to the Moon; that's 142 days by car

* It makes you lighter. With a surface gravity just one-sixth of that of the Earth, on its surface you'd be only one-sixth of your normal weight

* At 27.3 days, a lunar day lasts nearly as long as an earth month. We only ever see the near side – thus, the far 'dark side' imagined by Pink Floyd

* Mental illness has been associated with the Moon since ancient times: the word 'lunacy' is derived from the Latin 'luna'. 'Moon madness' was used as defence by a soldier accused of murder in 1940

* The Sea of Tranquillity sounds like the perfect holiday destination, but the 'seas' which cover 16 per cent of the satellite's surface are actually ancient lava flows

* Fertiliser not working? Try lunar gardening. Proponents believe lunar phases influence soil moisture as well as tide, and time their planting and pruning accordingly

* Four Nasa interns were charged with theft in 2002 after they attempted to sell Moon rocks they had stolen from one of the organisation's safes

* An astronaut marches on his stomach. On the day of the launch, the Apollo 11 crew were treated to a breakfast of orange juice, steak, scrambled egg, toast and coffee

* In 1999, six per cent of Americans believed the landings were faked. Hoax theorists point to photographic inconsistencies and a flapping flag as 'evidence' they were staged

* Why bother with diamonds if you can have Moon rock? In 1993, Sotheby's sold 0.2g of the stuff, collected by a Russian probe in the 1970s, for £442,500