An Astrophysicist Talks About the First Christmas Star

Christmas is all about twinkling lights. It’s one of the special things that makes this season so magical for little ones. And – of course – every year, it means we adults need to untangle the Christmas lights again from our box of decorations. Hey – I put these away so carefully back in January. Why are they in such a tangle now?!

Matthew’s gospel describes a star … a particular aspect of Jesus’ birth that is recorded in a curious way. He records that Magi (wise men from a King’s court) arrived in Jerusalem from the East. “Where is He who has been born King of the Jews? For we saw His star in the east and have come to worship Him.” (Matthew 2:2, NASB) Clearly they were putting 2 + 2 together here? Both an astronomical sign … and probably prophetic promises from the Jewish scriptures (our Old Testament). For example, Numbers 24:17 says,

I see him, but not now;

I behold him, but not near.

A star will come out of Jacob;    

    a scepter will rise out of Israel.[1]

But as these Magi continue their journey, the star is said to guide them. “…they went their way; and the star, which they had seen in the east, went on before them until it came and stood over the place where the Child was.” (Matthew 2:9, NASB)

It seems like an odd way of describing what was going on. But, like the other details we read in the Christmas story, it is very specific. It’s described from the perspective of people on the ground, but  how could a star be seen to lead these Magi?

Astrophysicist Luke Barnes observes that the great thing about cosmology is that you can wind time back and predict what was going on in our night sky at a point in history. So, we should be able to determine what was going on at the time of Jesus’ birth (around 5 BC, described here.) Luke says there are three main theories about what the “star” recorded by Matthew could have been.[2]


First – it could have been a triple conjunction of Jupiter and Saturn. When this occurs, from our vantage point on earth, we see the two planets cross over each other and so they appear much brighter in the sky and can be mistaken for a star. A triple conjunction is named this way because the crossover happens 3 times over a period of a month, or so. Appearing at different points in the night sky.

But did this happen at that time? There was one that occurred around 7 BC. But that seems a little early for Jesus birth.


Second – it could have been a nova or supernova, a vast nuclear explosion in space which is visible to us on earth. Astrophysicists are able to examine the remains of the star to work out when it blew up, so they can date the nova. Historical record and astro-evidence agree that a nova was visible in the sky in 1054 AD. We are not aware of one dated 5 BC (when Jesus was born), though Barnes admits we may simply not have found it yet.


Third – it could also have been a comet. The word for “star” is understood to be used by the ancients to refer to comets. Roman historians Josephus and Pliney both refer to them as signalling good or bad omens.

The thing about a comet is that it is indeed moving, and we can observe that from our vantage point on earth. So, over a period of weeks and months, it could conceivably be seen by the Magi from their perspective in the East, then the West and the South.

Of course, the thing about a comet is that it also has a visible tail caused be dust and gas being given off by the object as it travels thru space. Perhaps if the tail was seen as pointing upwards, then it could look to people like a pointer pointing down at a particular point, and so “standing over” Bethlehem. Also, the star and sceptre in that prophecy from Numbers 24 sounds like it could describe how a comet might look to the naked eye.

But are there any good candidates for this comet in history?

Haley’s comet was visible around 12 BC, which would be too early. However, Chinese astronomers claim to have evidence of a visible comet around 5 BC. The record is not very complete tho. There’s no record of it moving across the sky, although it would be reasonable to assume that it could have done that from the perspective of our planet.



While this subject has been debated for a long time, there seem to be reasonable candidates for the astronomical event described in Matthew’s account for the birth of Christ. But does a natural account of the star empty the story of any supernatural quality? After all, Jesus birth is described as being very special indeed. This wasn’t just any birth, it was the event when God came to earth to live as a person. Well, it seems to me that miracles aren’t just about God stepping into the physical universe at a point in time. They are also about God giving particular and special meaning to natural occurrences in the normal course of events. Surely, that could describe what was going on then in the night sky?

[1] Numbers 24:17, NIV.

[2] John Dickson, 12. First Noel, Undeceptions Podcast.


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I live in the UK, I'm married to Janet and I'm passionate about proposing a case for the historic Christian faith. You can find me on Twitter at @stuhgray.

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