As Santa does his annual Christmas Eve visits to homes around the globe he will be tracked by a billion dollar US defence radar system.

For the past seven years the North American Aerospace Defence Command (Norad), based under Cheyenne Mountain in Colorado, has been following Santa's sleigh and broadcasting his progress on its website.

The site will publish regular updates on his progress, along with photos from SantaCams around the world, and will even forward emails to the North Pole.

"Based on flight profile configuration data gathered from decades of Norad's radar and satellite tracking of Santa Claus, the scientists have concluded that Santa probably stands about 5 feet 7 inches tall and weighs approximately 260 pounds," the site says.

"From fighter aircraft cockpit photos, and other details Norad has gathered from SantaCams over the years, we know he has a generous girth, rosy cheeks from sleigh riding in cold weather, and a flowing white beard and hair."

Created in 1958, Norad is a joint American and Canadian organisation responsible for the air defence of the US and Canada using satellite and radar tracking.

But Norad may be onto a red herring, according to a seminal study of Santa physics published by Dr Arnold Pompos, formerly of Fermilab.

This postulated that Santa gets the whole job done in about 500 seconds by travelling at 99.99999 per cent of the speed of light, thereby solving the mystery of Rudolph's nose.

"The colour depends on just how fast Rudolph is moving, turning yellow, then green, then blue, then violet before becoming invisible in the ultraviolet range as he accelerates to higher and higher speeds," said Dr Pompos in his 1998 paper.

"This change of colour is a well-known phenomenon, called the Doppler shift, which astronomers take advantage of to figure out the speeds at which the stars and galaxies are moving in respect to us."

The Norad Santa website can be found here.