Near the end of When Ziggy Played Guitar, GQ editor Dylan Jones casually lets slip that he and the subject of his book have met each other "dozens of times". If the revelation comes as a surprise, that's because When Ziggy Played Guitar is light on first-person quotes from David Bowie himself. When they do appear, however, you find yourself wondering just how thrilling a proper Bowie autobiography would be. "For the likes of Roxy Music and myself, mascara was merely the conveyance by which great globs of non-rock flotsam and jetsam were to be delivered," he says on p171. "Japanese kabuki, Dada, Dietrich and Leni Riefenstahl, Piaf and futurism and, above all, 'elegant gloom'." Wow. If Bowie can deconstruct himself with such elegant precision in half a paragraph, imagine what he could do over the course of a memoir. A Keith Richards-style unburdening? A Chronicles?

While we await a definitive telling, there are 40-odd Bowie biographies from which to choose. Strictly speaking, Jones's offering isn't one of them. When Ziggy Played Guitar focuses on just four minutes of Bowie's 65 years: the Top of the Pops performance of Starman that beamed Bowie's unearthly alter ego into 15 million front rooms on 6 July 1972. But if every life has a moment that defines it, this was the moment it happened not just for Bowie but for many of the future pop stars who saw it. One of them, Marc Almond, recalls the battle lines drawn by one seemingly innocuous gesture: the effeminate draping of Bowie's left arm around the shoulder of his guitarist Mick Ronson: "Next day, all hell broke loose in the playground. Bowie was a queer, and if you liked him, you must be queer too."

Among older music fans, however, the world continued to spin on its axis. Anyone who cares to peruse NMEs of the period will note that Ziggy's arrival warrants no more exposure than any other moderately successful record of the age. Save for glam oddity Jobriath, far fewer of Bowie's contemporaries copied him than they did Led Zeppelin. For many critics, Ziggy was the last desperate act of a craven opportunist. A New Yorker writer flown to see the Ziggy shows fretted that "Bowie doesn't seem quite real". But, as long as music journalism has existed, performers  be it Bowie in 1972 or Lana Del Rey in 2012  have been docked points for their apparent lack of authenticity.

And, besides, it was those very notions of authenticity with which Bowie was playing when he created Ziggy. After several hapless reinventions, the only hit he had to show for his efforts was Space Oddity, but, as Jones points out, Ziggy Stardust was the result of a decade spent sifting through pop cultural detritus and working out which bits he could use to turn him into a pop star. Ziggy was created at a "granular" level. Jones holds almost every single grain up into the light for our inspection: the spaceman imagery that had provided Bowie with his sole other hit; an encounter with faded rocker Gene Vincent that had Bowie imagining Ziggy as a cross between Vincent and British-born rocker Vince Taylor; an eccentric American country singer who called himself the Legendary Stardust Cowboy. Also crucial to the conceit of Ziggy was a backstage encounter after a Velvet Underground show. Bowie assumed he had been speaking to Lou Reed; in fact, it was John Cale's replacement, Doug Yule: "That got my mind really working. About a rock star who wasn't real but in whom the audience  me  totally believed. I think that was probably the real beginning of Ziggy Stardust."

The resulting album, The Rise and Fall of Ziggy Stardust and the Spiders From Mars, told the story of an alien who lands on Earth with a message of hope in the planet's final years, but ends up destroyed by the resulting adulation. A record predicated on such a far-out conceit needed to impact upon a big audience. Which once again brings us back to that Top of the Pops performance. And yet Starman was the final song to be written for the album. Jones astutely zones in on Bowie's ambivalence towards the song that effectively gave him carte blanche to turn into a version of Ziggy long after the 1973 Hammersmith Odeon show that formally heralded his passing.

Jones's familiarity with the subject and the era he transcended frees him up to write with a flair and warmth that all but swallows you up: "Bowie was so thin he looked as though he'd spent the previous six months existing on a diet of nothing but the juice sucked from a wet mitten." On the life-sapping qualities of his own hometown, Jones recalls: "There were the caravan parks that looked identical to the parks the caravans were bought from (why did their owners bother attaching them to their cars and moving them?)"

One imagines that when Jones set about writing When Ziggy Played Guitar, he intended it as a celebration: not just of Bowie's most iconic creation, but also of the epiphanic effect a pop song can have on a generation. In fact, it's no less effective as a farewell to a pop landscape which allowed such epiphanies to happen. If 1972 were 2012, any artist who musters one hit single over three albums would be looking at an alternative career. In 2012, there is no Top of the Pops to bring the generation gap into the front room. In 2012, the generation gap is characterised not by arguments, but by the silence of earphones plugged into handheld devices. When this generation's Starman comes for your children, you'll barely even notice it.