What was the Star of Bethlehem?

For two thousand years, Biblical scholars have debated the nature of the Christmas Star. Now astronomers and other scientists are weighing in.

This month, it's impossible to overlook the brilliant planet Venus in the evening sky. During the Festive Season, it looks like a gleaming lantern hanging in the west, setting more than two hours after the Sun - a dead-ringer for the Christmas Star as it appears on our seasonal cards.

Was Venus the Star of Bethlehem? Almost certainly not - Venus makes such regular appearances as the "Morning Star" and the "Evening Star" that people observing the heavens even thousands of years ago would have been familiar with it. The Christmas Star must have been a celestial event that was truly out-of-the-ordinary.

Star of beauty, star of light - but if it was this bright, Herod would have known about it

To track down the real Star of Bethlehem, we need to know roughly the date of Jesus' birth. To confuse matters, Jesus wasn't born in the Year Zero (which doesn't exist), or even in Year One. Thanks to a miscalculation in the calendar by a sixth-century monk delighting in the name of Dionysius Exiguus, Jesus was actually born several years BC. We know also that Herod was alive at the time of the birth, and that he died soon after an eclipse of the Moon - almost certainly in 4 BC. So what astronomical portents were hoving into view at around that time?

We can rule out a really brilliant exploding star - or supernova - of the kind we see every year on our Christmas cards. Everyone in the Middle East would have been astounded by such a sight. Yet - according to St Matthew's gospel - neither King Herod nor his advisers
had seen the star. When the Magi turned up in Jerusalem demanding "where is he that is born King of the Jews?", Herod - with his authority in danger of being undermined - "enquired of them diligently what time the star appeared".

In addition, Chinese astronomers were logging their own observations of the sky at the time, and reported no brilliant supervovae. They did, however, record two bright comets. The first was Halley's Comet, which swings close by the Sun roughly every 76 years. An unforgettable view of the comet in 1301 so inspired the Italian Renaissance painter Giotto di Bondone that he used it as the model for his "Star" in a famous Nativity scene. But the ancient Chinese saw Halley swinging by in 12 BC - too early for the birth of Jesus.