Can science explain the mystery of the Star of Bethlehem?

There are many astronomy theories, though none has answered the questions over the birth of Jesus Christ

How did that happen?: the star led the Three Wise Men to baby Jesus in the stable at Bethlehem

Mary Evans

16 December 2016

What was the Star of Bethlehem? Was there some sort of highly unusual event in the sky around the time Jesus was born — supernatural or miraculous, or some sort of natural phenomenon that can be explained scientifically? We don’t have much to go on, just 12 verses from the opening of Matthew’s Gospel. So nobody knows for sure what the star was. But we can make some educated guesses.

If it was an astronomical event, it must have been something extraordinary. Usually, stars are orderly and predictable; after all, that’s why we can use them to fix our calendars and guide our ships. But there are exceptions.

Supernovas are spectacular; some can even be seen in the daytime. And they are rare — the last naked-eye supernova in our galaxy was observed in 1604. (Another could be seen in our near-neighbour galaxy, the Large Magellanic Cloud, in 1987.) But ancient astronomers such as the Chinese were very careful about recording such events, and they have no record of a supernova around the time Jesus was born. Furthermore, supernova remnants are quite prominent sources of radio emissions, which can tell us how long ago the event took place. There are no such remnants visible to us from 2,000 years ago. Astronomy can pretty much rule out a supernova.

Comets are spectacular, and most come at unpredictable times. (Predictable comets such as Comet Halley are famous precisely for being so unusual.) We can’t rule out a bright comet at just the right moment, 2,000 years ago. But in ancient times comets were universally interpreted as signs of doom, not a joyful event like the birth of a king or messiah.

Nowadays most scientific explanations look for unusually close approaches of bright planets, called “conjunctions”. For example, the 17th-century astronomer Johannes Kepler used his new theory of elliptical planetary orbits to calculate that there was a particularly interesting series of conjunctions of Jupiter and Saturn in 7 BC.

These days, anyone can select a date — say, December 25, 1 BC — and plug it into a planetarium software app to see where the planets would have been. (Of course, no one really knows Jesus’s exact birth date. And in any event, historians now realise that when Dionysius Exiguus in AD 525 started the tradition of counting years from the birth of Christ, he miscounted slightly.) The trick is to find something that happened when King Herod was alive, and probably in the spring when shepherds would be likely to be out at night tending their flocks; something that would indicate the birth of a king; something that indicates Judea as the location of this birth; and, finally, something consistent with the apparent fact that only astrologers were wise to this event. That’s a lot of constraints.

One elegant modern theory I particularly like comes from a book by the astronomer Michael Molnar, Star of Bethlehem: The Legacy of the Magi. He uses the well-known astrological alignment of planets and the sun at the birth of emperor Augustus, which he claimed as evidence of his own destined royalty, to argue that such an alignment of planets was the sign of kingship. The key to the alignment was having the planets rise with the sun — what is called a “heliacal rising”. And since nobody would actually be able to see the planets rising, given the presence of the sun among the planets, only an astrologer calculating the planetary positions would know when this occurred.

Molnar finds just such a grouping of planets in the constellation Aries (which was associated with Judea) in late March of 6 BC, and again in April. And that is the year, he tells us, that historians have identified as the most likely year of Jesus’s birth. It sounds quite convincing. It’s all quite neat. And, indeed, it’s rather startling to realise that such an event really did occur in the sky about the time Jesus may well have been born. If you have a planetarium program, you can look it up for yourself.

But was this really what Matthew was talking about? Search for “Star of Bethlehem explanation” online and you’ll find more than 40,000 hits, each site proclaiming that it has the one true explanation for the star. And each gives vigorous arguments why all the other theories are obviously no good. No one knows enough to argue convincingly which of these theories would provide the best scientific explanation for the star. Astronomy turns out to fail us — not for having no answer but for having too many possible conclusions.

Furthermore, for all we know, the star might have been a purely miraculous event. Or Matthew’s story could have been invented by him to emphasise the kingship of the Messiah. In our passion to explain the star, we can’t lose sight of where it was meant to guide us. Its exact nature is neither the more important nor the most interesting part of the story.

At the Vatican Observatory, our work is the same as any other astronomical observatory. We take new data about things in space and try to devise explanations for how they behave. But we’re interested in the Star of Bethlehem for the same reason that everyone else is: it’s a fun mystery, a place where science and hope intersect.

Actually, to me the most astonishing part of the story of the Magi is not that they would predict the birth of a king from the positions of the planets; any fortune teller could have done that kind of calculation. Nor is it that they’d pull up roots and travel afar to find out if they were right; we astronomers do that all the time. Instead, it’s that they would be able and willing to recognise the king they were seeking in the child they found in a manger.

Br Guy Consolmagno SJ is the director of the Specola Vaticana, the astronomical observatory of the Vatican City state

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