Star of wonder

A comet, an eclipse, a supernova, an alignment of planets - was the Star of Bethlehem, said to have led the wise men to the Baby Jesus, a real astronomical event? Some 2,000 years ago, wise men saw an incredible star shining over the Holy Land. It was their signal to embark on an epic journey to visit the new Messiah. But what exactly was the Star of Bethlehem?

Modern science is unravelling the mystery behind one of the most famous astronomical stories in history. New developments in technology allow astronomers to map the ancient night skies with extraordinary accuracy.

As they study the movements of the planets and stars, experts are challenging the traditional assumption that it was a blazing comet - instead there are several unusual astronomical events that the wise men could have seen in the skies. The Bible tells us remarkably little about the star, with only the Gospel of St Matthew mentioning it. He records the wise men asking: "Where is he who has been born King of the Jews? For we have seen his star in the east and have come to worship him."

No date or detailed description is given. Even the identity of the men is obscure. Rather than the kings of popular imagination, the wise men are thought to have been priests from Persia, known as Magi. Keen astrologers who looked to the stars for guidance, the Magi combined science with faith to predict the birth of a new Messiah.

So what prompted them to travel to Bethlehem? Most experts agree Jesus was born in 4BC or earlier, as King Herod, who ruled over Judea at the time, is recorded as dying in 4BC. Now astronomers have identified four celestial events in this period that could have been the Star of Bethlehem.

Triple conjunction of Planets

An ancient clay tablet, now in the British Museum, is a key part of one theory which says the star was a rare series of planetary meetings, known as a triple conjunction.

This happened between Jupiter and Saturn and occurred in the night sky in 7BC, says Dr David Hughes, emeritus professor of astronomy at the University of Sheffield.

Jupiter, the royal star, and Saturn came together three times over several months. Significantly, this happened during the constellation of Pisces, a sign associated with Israel.

There is evidence on the clay tablet that Persian astronomers predicted this. The tablet calculates solar, lunar and planetary activity for that year, and describes the conjunctions.

Eclipse of Jupiter

A 2,000-year-old coin, minted north of Judea, is part of the evidence behind another theory. Dr Mike Molnar of Rutgers University, New Jersey, believes the star could have been an occultation, or eclipse, of the moon with Jupiter on 17 April 6BC.

He argues the Magi saw the star in the constellation of Aries, not Pisces. The coin depicts Aries the ram leaping across the sky and looking back at a star.

According to astrological texts from the time, Aries ruled over Judea, with Jerusalem as the capital of the Near East, making it the sign of the Jews.

Dr Molnar believes the Magi saw this eclipse. Just before sunrise, Jupiter would have risen in the east, just as St Matthew describes their sighting of the Star. Then, as the moon passed directly between Earth and Jupiter, the kingmaker planet was hidden from view.

Supernova

Some think the star could have been a much bigger celestial event. European Space Agency astronomer Dr Mark Kidger believes it would have taken more than unusual planetary movements to persuade such seasoned astronomical experts to travel to Judea.

The Magi could have seen a star entering its supernova phase, one of the most energetic and explosive events known to astronomers.

He has even identified a candidate - DO Aquilae - which erupted in 1927 and is likely to have erupted several times previously. If it had erupted 2,000 years ago, the Magi would have seen it just above the horizon, in the east.

He hopes radio telescopes in the future will be able to detect a faint bubble of expanding gas around Aquilae and calculate when exactly the bubble started to expand.

Two planets looking like one bright light

One theory has the most surprising twist. The date for celebrating Christmas was only fixed centuries after the event - and is questioned by many - but Texan law professor and astronomer Rick Larson believes Jesus really could have been born on 25 December. But on 25 December 2BC.

Unlike other astronomers, he has looked at later celestial events because he thinks the calculation of King Herod's death is inaccurate. The 4BC date is based on the writings of the historian Josephus, but every Josephus manuscript he has studied dating before 1544 is consistent with Herod having died in 1BC.

In 2BC Jupiter met up with one of the brightest stars in the sky, Regulus, known by the Magi as the "little king". Nine months later, Jupiter met Venus, known as the mother planet. These meetings would have been symbolically significant, as was the timescale involved.

The planets would have seemed so close they would have looked like one bright light in the sky. Professor Larson believes this light was what prompted the Magi to travel to the east. As they made their way, Jupiter continued to move across the sky until it appeared to stand still over Bethlehem.