How the passing of time changes perception: in 1969, no one could fail to be astounded by photographs of an American astronaut walking on the Moon. The future had arrived in front of our eyes, promising a new era in which anything seemed possible. The human race had conquered space and there seemed no limits to what might be achieved in the next decade or so.

Forty-three years later, pictures of the Moon landings are quaint and a little sad. In his unwieldy space suit, Neil Armstrong looks like a figure out of an old sci-fi movie, and the announcement of his death at the weekend feels like a coda to a book which has long been closed. Six Apollo missions landed a dozen men on the Moon between 1969 and 1972, but predictions of human beings living there, and space tourism becoming a reality, were way off the mark. The current rover mission to Mars has opened a new era in space exploration, but I doubt whether anyone would have predicted that it would take so long.

The tributes paid to Armstrong in the past couple of days have been heartfelt. The tone was set by President Obama, who described the astronaut as "among the greatest of American heroes". Obama's remarks caught the public mood, reflecting a craving for authentic heroism in an age when the word is used so widely that it's in danger of being devalued. Armstrong responded to his global fame with quiet modesty, never losing sight of why he had got involved in space exploration in the first place. He described himself as a "nerdy engineer" and insisted that he took "a substantial amount of pride in the accomplishments of my profession".

These days, Armstrong would barely have landed on Earth before being inundated with offers from reality TV shows ("I'm an astronaut, get me out of here"). But if Armstrong's determination to continue with normal life strikes us as charming, it also evokes powerful feelings of nostalgia. It's easy to look back from the standpoint of 2012 and see him as the representative of a more innocent world, untouched by so many of the developments we dislike about our own time.

In 1969, Richard Nixon was in his first year as President and the term "Watergate" had not entered the political vocabulary. The sheer excitement of watching grainy pictures beamed back from the Moon obscured any connection between the space race and the Cold War; Apollo 11 was simply a crowning achievement, marking a new chapter in human endeavour. Three months later, two million people took part in protests across the US against the Vietnam conflict, which the 1968 generation rejected as yet another old men's war.

The peaceful use of science, symbolised by the Moon landings, promised a glowing future in which humanity would rise above the conflicts which had disfigured the first half of the 20th century. In 1963, Harold Wilson had told the Labour Party conference that "we are redefining… our socialism in terms of the scientific revolution". Most people know the next line of Wilson's speech, which talked about "the Britain that is going to be forged in the white heat of this revolution", although they may have forgotten that he followed it with a swipe at the trade unions. Wilson's image of a new country being created in the purging flames of a furnace was far from the reality of Britain's smoky industrial cities, but the belief that we were entering a period of cheap and abundant energy was widespread.

Back in 1952, the Daily Graphic had somewhat optimistically compared the arrival of nuclear power with "stepping out of the Ice Age into a world of permanent sunshine". The popular British TV programme, Tomorrow's World, had more grounding in reality, but was not immune to flights of fancy about robots relieving human beings of annoying household chores. Nixon was a scoundrel, but he wasn't George W Bush, and the success of the US in the space race marked a high point in its history. Under Reagan, space exploration was eclipsed by star wars, and we've become used once again to technology being used to find more sophisticated ways of killing human beings.

But that's not the only reason, I suspect, that the death of an astronaut has moved so many people. Armstrong was an aeronautical engineer who became, almost by accident, the first human being to step foot on another celestial body. He did so at a time when science was in the ascendant, debunking superstition and religious ideas about how the world came into being. The Apollo missions belong in a world which would have found it impossible to imagine 9/11 or the wars that followed it. The last century's conflicts, driven by ideology, have been replaced by wars in which religion once again plays a leading role. Who would have believed, in the 1960s, that individuals in search of a shortcut to paradise would one day immolate fellow human-beings in horrific suicide-bombings?

The Moon landings were expensive, grandiose even, but they expressed an optimism and thirst for knowledge which are the hallmarks of secular culture. We are sorely in need of a new enlightenment, based on a rational, scientific and endlessly curious view of the world. I would like to think Neil Armstrong will be one of its heroes.

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