BBC Science Correspondent Sue Nelson: Follow Santa's progress on the Net

As Santa delivers presents around the world, Norad - the North American Aerospace Defence Command - will use their satellite surveillance network to keep track of him.

"It's a thumbs up for Santa's move into cyber space," said Danny Meadows-Klue of The UK's Electronic Telegraph.

Fighters are sent up to locate Santa

"There are a lot of Santa Websites out there but there's nothing else on this scale, which lets you watch him fly round the world on his sleigh."

Norad has been monitoring Santa's progress on Christmas Eve since the 1950s, but this year's satellite-to-Internet link-up is bringing the latest technological tools to Santa watchers.

Major Jamie Robertson on calls to Santa at the Combat Operations Centre

It all began thanks to a misprint. An advertisement for a local store in Colorado Springs, home to Norad, invited children to call Santa on a special hotline. The misprint meant that the hotline they called was that of Colonel Harry Shoup, Norad's Director of Operations.

Realising what had happened, Colonel Shoup had his staff check radar data to see if there was any indication of Santa making his way South from the North Pole. There was and a tradition was born.

Norad is responsible for warning of any missile launches against America or Canada but at Christmas time all their computer wizardry is used to track Santa's sleigh.

But because Santa tends not to file a flight plan, Norad has to confirm the identity of the "unknown" Christmas object by scrambling two Canadian jets to the far North of Canada.

Heat detection

As he travels through North America, Norad's extensive radar networks keeps tabs on him. As he travels further away, their satellites, 22,300 miles above the Earth's surface, pick up the trail.

Defence equipment put to a different use

These detect heat in the form of infra-red radiation that would be given off by missiles. But in this case, they use the heat coming from Rudolf the Reindeer's red nose. "If Rudolph were to take a day off, we would be in trouble," say Norad.

Norad's Website explains how Santa makes his marathon journey all in a single night. "The fact that Santa Claus is more than 15 centuries old and does not appear to age is our biggest clue that he does not work within time as we know it.

"His Christmas Eve trip may seem to take around 24 hours, but to Santa it could be that it lasts days, weeks or months. The only logical conclusion is that Santa somehow functions on a different time and space continuum."

Roger Highfield: We know what Santa can do

A recent claim by a magazine that the speed of Santa's sleigh would cause the reindeer to burst into flames has been firmly rejected by the author of "Can reindeer fly?", Dr Roger Highfield.

"The spy magazine allegation is outrageous," he told the BBC. "We know Santa delivers those presents on Christmas Eve as reliably as we know that Rudolf's nose is red. He obviously resorts to all sorts of leading edge technology - heat shields to protect the reindeer and warp drives."

Santa will be tracked passing some familiar landmarks around the world, including the Mir space station and New York's Statue of Liberty. His position will be updated hourly during his worldwide trip.