LONG ago, we are told, three wise men followed the Christmas star to Bethlehem.

More than 2000 years later another group of sky watchers have observed a heavenly Christmas tree, complete with shining blue baubles.

It's actually an enormous cloud of gas and stars, about 2600 light years from Earth, and first seen in the 1780s by William Herschel, who is best known for discovering the planet Uranus.

Now astronomers at the European Southern Observatory, 2400 metres above sea level in the mountains of Chile's Atacama Desert, have celebrated Christmas by snapping a sharp new picture of the cosmic decoration.

Dubbed the Christmas Tree cluster, its branches appear red, the observatory announced in releasing the picture, "because the huge gas clouds are glowing under the intense ultra-violet light coming from the energetic hot young stars.

"The stars themselves appear blue as they are hotter, younger and more massive than our own Sun. Some of this blue light is scattered by dust."

The observatory added that when viewed through small telescopes, whose lenses turn images upside down, "the stars resemble the glittering lights on a Christmas tree."

To make the picture, the observatory "stared at the cluster for more than 10 hours through a series of specialist filters to build up a full colour image of the billowing clouds of fluorescing hydrogen gas".

The triangular feature on the top of the tree, yet more gas illuminated by bright stars, is aptly called the Cone Nebula.

Astronomers study the celestial Christmas tree, part of a vast region of star formation, to learn about star birth. Located close to the Orion constellation, the Christmas tree picture is about 30 light years across.