What was the Star of Bethlehem? Over the years many astronomical explanations have been suggested.
What did the Bible say?
It's interesting to note what was originally included in St. Matthew's Gospel, and what has come down to us as interpretation or embellishment. For example, there is no mention of there being three kings, only 'Magi' (wise men, magicians or possibly astrologers) who left three gifts. The Greek word generally translated 'star' (αστερα - astera/astra from which we get 'astronomy') can also mean planet or could refer to other objects such as a comet. There is no mention that the star is particularly bright, and nor does it seem to have significance for anyone other than the Magi.
There have been at least five purely astronomical explanations for the Star of Bethlehem...
1. Was it a nova or supernova explosion?
The idea that the Magi saw a nova or supernova explosion was hinted at by 17th Century astronomer, Johannes Kepler, and has had many supporters since then. However, there is no Western record of such an event and the Chinese records only have one possible mention of a nova or supernova over the potential time for Jesus' birth. There is also no known supernova remnant, which we would expect to find if there had been a supernova at the birth of Jesus.
2. Was it a comet?
This explanation has its origins even further back in time, dating to early Christian theologian Origen in AD 248. Again Chinese records can be invoked but give no good support apart from the potential 5 BC nova/comet. One advantage of the comet theory is that comets move across the sky. It had been argued that this fits the interpretation of the Gospel that the star moved as it directed the Magi. Though this same argument could be applied to an object moving with the stars if the journey of the Magi took some months. Most classical depictions of the nativity show the 'star' as a comet.
3. Was it a conjunction of Jupiter and Saturn?
Kepler is also associated with the idea that the close conjunctions of Jupiter and Saturn were the event associated with the 'star'. In fact there were three conjunctions, when the two planets were close to one another in the sky, but none of these were close enough that they'd appear as one object. For this reason most analysts reject this theory, though such an event could have been of religious or astrological significance.
4. Was it a stationary point of Jupiter
Jupiter, in its apparent path across the sky, is generally seen to move from east to west across the starry background. Due to the relative movements of the Earth and the planets this motion appears to slow and then stop as the planet reaches what is called a stationary point. The planet then appears to move from east to west for some days before again stopping and resuming its west to east movement. At the possible time of the birth of Christ one of the stationary points could have occurred when Jupiter was directly overhead at Bethlehem at the same time of night for several nights. The disadvantage of this explanation lies in the lack of any rarity in the phenomenon as it would happen every year.
5. Was it a conjunction of Jupiter, Regulus and Venus?
One other possibility includes a set of conjunctions of the planets Jupiter and Venus, and the bright star Regulus. In this case, the mythologies associated with the objects become important. Jupiter in Hebrew is known as ‘Sedeq’ which is often translated as meaning righteousness, and is often viewed as being the king of the planets. Regulus itself is Latin for prince or little king and Venus is often viewed as a symbol of love, fertility and birth. As such, the combination of these objects close in the sky could have led to the interpretation of the birth of the King of Kings.