It’s that time of year again. At the North Pole Santa’s helpers are getting the gifts ready and the countdown to lift-off on Christmas Eve has begun.

Now you may not believe in Santa but the North American Aerospace Defense Command, or NORAD, knows he is there. This bi-national military organisation keeps an eye on anything that enters US and Canadian airspace, including flying reindeer and chubby men in red suits on a sleigh.

So it has made sure that all the preparations for its annual Santa tracking are in place, and this year you can also track his flight in 3D using Google Earth.

But why does NORAD track Santa? After all some people say he doesn’t exist. He certainly doesn’t file flight plans with organisations such as the UK’s Civil Aviation or the US Federal Aviation authorities.

The programme actually began by mistake 53 years ago. US retailer Sears, Roebuck and Co printed the wrong phone number in a ‘Call Santa’ advert. The calls went through to the director of operation’s desk at NORAD and that, as they say, was that.

The how is also as important as the why. The physics behind this 24-hour round the world trip carried out by one jolly old man in an old wooden sleigh pulled by nine ordinary reindeer continues to baffle the best brains, especially since his list of children gets bigger every year.

NORAD says that it is able to track the journey thanks to Rudolph's red nose. It apparently emits a significant infra-red heat source that is enough for NORAD’s satellites to maintain a sufficient lock during his 24-hour journey.

In order to make it around the world, by NORAD’s calculations, Santa has clocked up to 600 times the speed of sound. However, one theory it has put forward as to how, despite the phenomenal speed, Santa can complete his task in 24 hours is he operates in a different time-space continuum to us.

The heat factor has also been discussed by many scientists. If we went as fast as Santa and the reindeers the enormous heat generated would be sure to fry us to a crisp. So why don’t they burn up?

A few years ago Norwegian internet magazine forskning.no put this question to astrophysicist Knut Jørgen Røed Ødegaard. His theory was that Santa has an ion shield of charged particles, held together by a magnetic field, surrounding his entire sleigh.

Will we ever solve the mystery? It’s unlikely. Santa is special after all. But before they go to bed tonight, children everywhere can log on to NORAD’s site and track his progress.

Happy Christmas to all, and to all a good night!