A certain absence of subtle, luminous radiation characterises this Ashes series. So said the England captain, Andrew Strauss, before the third Test began. “I do not think this Australia side has an aura about it,” he said. He added, wisely and accurately, that this doesn't mean the Aussies are not good and it doesn't mean they can't win. But if they do so, they will have to do it without the help of the aforementioned subtle, luminous radiation.

And Lord, I've seen what an aura can do. Seen it in Ashes cricket, seen it in cricket all over the world, seen it in every sport in the calendar. Shane Warne had an aura. So let's see what an aura can do before we try to find out what it is. Brace yourself, for we must go back to Adelaide in 2006.

England had won the Ashes in 2005 and fancied themselves as a half-decent cricket team. In the second Test, despite losing the first, they scored 551 for six declared. Australia responded in kind on a “bat for ever” pitch, so England were seeing out the draw at 69 for one. Enter Warne.

Now Warne, as we know, is the finest spin bowler that ever drew breath. But that is not the full story. That doesn't explain how he scaremongered England to defeat on that awful sunny afternoon. There was something more than excellence involved here.

First, he convinced the umpire, Steve Bucknor, that Strauss had edged one on to his pad; the umpire slave to reputation rather than servant of the situation. Ian Bell was run out. Then Kevin Pietersen was bowled round his legs trying to sweep Warne. All at once, England were in a panic, all out for 129 and Australia knocked off the runs they needed to win.

This was not a victory for spin bowling. This was a victory for the aura of Warne; the aura of Warne and the rest of the Australia team. There was no rational reason why England should have lost, still less collapsed. But Warne's subtle, luminous radiation was too much for them.

Of course, we saw the reverse thing happen in 1981, when Ian Botham, a cricketer with an aura if ever there was one, did what he liked with an Australia team that included Border, Lillee, Marsh and Alderman. It is something that Australia did regularly from 1989 until 2005, and at many other points in history, not just through excellence, because their cricketers - Dennis Lillee and Don Bradman, to name but the greatest - had something beyond mere excellence.

Aura. A term borrowed from New Ageism, from parapsychology. It's an emanation. A sort of all-around halo. Aura enthusiasts will tell you that a halo represents the aura in Christian art. They will then point to other auras, such as those around representations of the Buddha. An aura had always represented particular power or holiness. You can see an aura with your third eye, apparently; some will tell you that an aura has colours and that it comes in seven layers.

So we have borrowed this concept and used it in a way that will no doubt irritate the devout New Agers - in so far as these enlightened people are subject to irritation - by using it loosely, to imply this something-other, this something-extra, this powerful emanation of personality.

And it is something we find most vividly in the sporting world, vividness being what the sporting world does best. In sport, we use the term “aura” for the winners: for athletes whose excellence seems to have more about it than mere ability. Almost as if it really was some kind of inner radiance.

Roger Federer was one of the greatest exploiters of aura in sporting history. He held the No 1 spot in tennis for a record 237 weeks and wielded that ranking like a razor. People expected to lose against him. He could extort deference from his opponents, a deference that was not entirely owing to his suite of skills. Certainly, his skills were vast, but his aura made them appear still vaster.

But Rafael Nadal began to beat him repeatedly on clay, expanded to beat him at Wimbledon and then at the Australian Open, leaving Federer in tears. Federer's aura was in tatters, there for the taking by anyone with the skills to match him.

But with Nadal knocked out of this year's French Open and injured for Wimbledon, Federer refound his highest skill level and patched up his aura. Without his rival, he is back at No 1, invincible . . . and waiting in quiet dread, in itching eagerness, for the time when Nadal is fit again.

You can find players with an aura in all sports and it is something generally associated with greatness. Pelé had it, and Franz Beckenbauer. Ayrton Senna and Lance Armstrong possessed it: the ability to force from their opponents the feeling that beating them would violate some sort of cosmic order.

There have been great athletes who won great events without the help of an aura. It is not an indispensable part of greatness. Steve Redgrave was increasingly vulnerable, likewise Matthew Pinsent, but they won their vast collections of rowing gold medals - rowing is not a sport in which auras help much, in any case - with the help of something else. Michael Phelps had the same thing in the Water Cube at the Olympic Games in Beijing - something hidden, rather than something visible. But that must be a story for another day.

Usain Bolt had an aura in the sprints at the same Games, and if his pure speed would have won his races no matter what radiance he possessed, there was no disputing the sense of specialness that surrounded him by the time he settled down on his blocks in the 100 metres final on that fabulous Beijing night.

We are forced, then, to seek some kind of definition. We can identify an aura, all right. An aura is possessed only by the excellent, but it is not necessary to have one to achieve excellence. There are even players with an aura - Andrew Flintoff, perhaps Pietersen - who have not consistently reached excellence.

Aura is something many great athletes possess. It manifests itself as the ability to get slightly more than even their own lofty abilities are worth. I suspect it comes down to our perception of excellence: if you really are that good, then you must be even better. You must be well-nigh perfect.

The willingness to concede absolute specialness - to see an exceptional performer and to believe that the performer is even better than he is - goes right to the heart of what an aura does to people. The question of whether it comes from the aura-possessor, or from the aura-perceivers, is one I will leave with New Age scholars, sports psychologists, beaten opponents and the glorious victors themselves.

All I can tell you is that I have seen athletes who seem to be blessed, who believe themselves blessed. Even their opponents - despite themselves - are forced to believe that these special athletes are blessed. And while the aura-free Ashes will continue to give us a glorious and complex drama, it is the players with auras who bring us the very highest levels of enjoyment - and pain - that sport can bring.