They form when all the planets are in alignment, when there is a simultaneous emergence of a group of uniquely talented athletes in the same generation, to combine as a dominant team or compete against each other as individuals. Either way, they attract a beam that can illuminate a sport across the generations.

As this year's National Hunt season matured and progressed there were indications that in retrospect, something unusual had occurred in Irish novice hurdling a couple of seasons back.

This week's festival at Punchestown should confirm it.

Irish racing seems to have found itself a cluster.

Clusters are, of course, found in all sports, not just horse racing. A generation ago some trainers and mentors supervised sessions for the Kerry minor and under-21 football players without even dreaming that the spotty kids they were yelling at would take enough medals back to the Kingdom in the next dozen years to cause a run on the price of precious metals.

Similarly, the NBA probably didn't immediately recognise the significance of the last two college drafts of the 1970s, but by 1984 Magic Johnson and Larry Bird had redefined and revolutionised the sport of professional basketball in the United States. Then Michael Jordan joined the league. By the time these three contemporaries hung up their endorsements and Nike court shoes they had transformed their game from a niche product into one of the most lucrative sports on the planet.

Similarly, golf was a stuffy and elitist country club pastime until Arnold Palmer first made it accessible to the common man in the 1950's, but it was his subsequent rivalry with Jack Nicklaus and Gary Player that raised the sport to a new level and to the billiondollar industry it is today. If the crowding on the tee boxes this morning ruined your game, these three shoulder much of the blame.

A sport as old as horse racing has, of course, experienced many of its own rich clusters through the years. Brigadier Gerard, Mill Reef and My Swallow, separately among the best milers in history, all happened to be born in the same year, 1968, ensuring that their three-year-old classic season was one of the most memorable in history.

As these three were battling at the finish of the 2,000 Guineas at Newmarket, Night Nurse and Sea Pigeon were trotting beside their mothers in a paddock and were joined on earth the following spring by Monksfield. Ten years on these three great rivals were in the middle of what is still defined as a golden age of hurdling and between them, they have won six consecutive Champion Hurdles. Their epic battles are warmly remembered and still regularly feature in polls of the greatest races ever.

The longevity and familiarity of National Hunt horses distinguishes them from their flat counterparts, and this helps clusters form, mature and continue. The one season spent novice hurdling is a key element of the rites of passage for young and inexperienced horses, and is usually sandwiched between a bumper season and graduation to the world of grown up contests. Novice hurdlers are racing's equivalent of youth or academy teams at soccer clubs.

Each year it is to be expected that a couple of the batch will emerge and go to excel at senior level, but every so often there will be a group such as the famous Manchester United youth team of the early 1990s. The group of players that contested the FA Youth Cup finals of 1992 and 1993 included David Beckham, Ryan Giggs, Paul Scholes, and the Neville brothers. Admittedly Robbie Savage was also part of that team, but even so, it still counts as a cluster.

The realisation that our equine minors of 2004 were an exceptional bunch has gradually become glaringly obvious.

If they further establish their credentials this week at Punchestown, it will signal the beginning of an era, and in its own way should rival those of the Jordan NBA years, the Nicklaus rivalry with Palmer or the Kerry harvesting of Sam Maguire in the late 70s and early 80s.

As it was 12 months ago, the three major divisional Cheltenham champions are all trained in Ireland. Otherwise nothing is the same. This time last year it would have been long odds against Moscow Flyer, Kicking King or Hardy Eustace failing to retain their crown at the festival, and even longer odds that three hometrained horses would replace them. It is more remarkable that all three of the new champions emerged simultaneously as a cluster from the novice hurdlers of two years ago.

In hindsight, there were two key races that spring. At the Hennessy meeting at Leopardstown, Brave Inca won the Deloitte Hurdle by three quarters of a length from Newmill.

A month later Colm Murphy's stable star won the Supreme Novices' Hurdle at Cheltenham, beating War of Attrition by a neck.

Brave Inca's running style misled people and gave rise to a prevailing wisdom that the Irish novices looked fairly average that year and were likely to be eclipsed in the longer term by English rivals such as Ingles Drever, Fundamentalist and Royal Shakespeare. Now that we know that Brave Inca is a complete hard chaw, who only seems to enjoy a race if there is a serious row at the end of it, his narrow victories were initially badly underrated. Not for the first time in racing, the prevailing wisdom got it completely wrong.

War of Attrition is now the Gold Cup winner, Newmill spread-eagled his field in the Champion Chase and Brave Inca justified favouritism in the Champion Hurdle. All three will bid to add the Punchestown version of their Cheltenham victories in a mouthwatering week of racing at the Kildare track.

One of the other intriguing elements of the week is to see just how deep this cluster runs. In the ACC Bank Champion Hurdle on Friday, Brave Inca defends the title he gamely won last from Harchibald.

The main dangers include Macs Joy, Essex, Al Eile and Asian Maze . . . all Grade One winners at senior level, and, obviously all novice hurdlers in 2004.

Absent through injury is another of that year's bunch, Feathard Lady, potentially the greatest of them all. Feathard Lady and Asian Maze are the best mares this country has produced since Dawn Run and it's incredible that they have both emerged at the same time, to form their own subcluster. This is the race of the season and if Feathard Lady was fit to run, it could arguably be the race of the decade.

Newmill and War of Attrition face less arduous tasks in confirming their Cheltenham superiority, and even if Brave Inca is beaten the chances are the winner will have emerged from the 2004 novice vintage. Enjoy this generation of horses while you can, they don't come around too often. Clusters.