6 Theories about the Star of Bethlehem

What was the Star of Bethlehem? Recorded only in the Gospel of Matthew, this mysterious celestial object is said to have heralded the Nativity. For millennia stargazers have wondered what it may have been.


Image of mystery of xmas-star

The Mystery of the Christmas Star is our popular seasonal show (Image credit: Evans & Sutherland)


Now when Jesus was born in Bethlehem of Judea in the days of Herod the king, behold there came wise men from the east to Jerusalem, saying “ Where is he that is born King of the Jews? For we have seen his star in the east, and are come to worship him”. . . . and lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was. When they saw the star, they rejoiced with exceeding great joy.

Matthew 2: 1-2, 9-10

It is widely known that Jesus was born sometime between 4 and 8 BC, and certainly not in December.  Historical records show King Herod to have died early in 4 BC so Jesus must have been born before then. The Wise Men or Magi were almost certainly Zoroastrian astrologer priests from Babylon or Persia. As such they would have been skilled observers of the night sky with a lifetime of experience. Such men would have been familiar with virtually every celestial event visible to the unaided eye.

If the star observed by the Magi in the east really moved across the sky until it halted to hang over where the young child lay, we have moved beyond astronomy as no natural object or event could do this. Such a unique spectacle would have witnessed by many across the East, including Herod (who was unaware of its existence until the Magi told him) and would have been recorded in established history. Let assume that Matthew’s words do not wholly reflect history but the Magi’s journey was prompted by their sighting a real astronomical object. What could this phenomenon have been? Let us investigate some possibilities.


A meteor is the spectacular demise of a tiny scrap of metal and stone slamming into our planet’s atmosphere at tens of kilometres per second. Kinetic energy is rapidly transformed into heat and light as the speck of interplanetary debris is vaporised perhaps a hundred kilometres above our heads. Occasionally, larger meteors fall appear as dramatic fireballs (or bolides). These can be very bright and can be colourful, blazing in startling golds or greens. Yet these are sudden and fleeting events, over in seconds, impossible to reconcile with the Biblical account. They would also been known to the Magi.


A comet is a small ice-rich body from the chilly darkness of the outer Solar System. Swinging sunwards along a slow orbit, the comet melts in the Sun’s unfamiliar heat. Escaping gas and dust can form great glowing tails stretching across the sky for weeks.  As early as the 2nd Century AD the church father Origen (c 184–c254) suggested that the star described in the gospel of Matthew was a comet.

Astronomy worldwide owes much to the astronomers of China. For millennia, Chinese imperial dynasties employed stargazers who accurately recorded what they saw in the night sky for the creation of horoscopes and calendars. We can still read these ancient records today, and they are invaluable and reliable resources for explorers of the skies of the past. According to these Chinese records, two comets appeared in the period when Jesus was born, one in 5 BC and a second in 4 BC. The comet of 5 BC was first observed in the constellation of Capricornus in March  or April, and was visible for 70 or more days. To the fastidious scholars it was a “sweeping star” or “broom star,” presumably had a pronounced tail.  The comet of 4 BC, was recorded in April 24 in the constellation of Aquila. It was described as a “po,” comet meaning “tailless”. Unfortunately to the Magi (and throughout the cultures of the Mediterranean and Near East), comets were universally seen as harbingers of disaster. It is hard verging on impossible to see how they would have interpreted a comet as a good omen.


Image of Giotto's Adoration_of_the_Magi

Giotto based his Star of Bethlehem on Halley’s Comet (Image credit: Adoration of the Magi by Giotto di Bondone (1267–1337))


Planet or Star

Bright planets such Jupiter and above all Venus be arresting sights in the evening or morning sky. Observers can tell they are something other stars and this can (and I write from experience) lead to thoughts of alien spaceships hovering in the night or the belief that this must be a contemporary return of the Star of Bethlehem. Ever that brightest of stars, Sirius can surprise some. I once had a long but pleasant telephone chat with a gentlemen who (from his description of where and when he was looking skywards) had been observing Sirius in the December sky. The caller was convinced that he was seeing the Star of Bethlehem, it was common knowledge in his area, he told me, that it appeared in the sky every forty years or so and that he had last seen it in his boyhood.

It is extremely unlikely that the Magi could have seen such familiar objects as these to be prophetic events.


Image of_Sirius

Sirius blazing in the December sky startles many with its brightness (Image credit: NASA/ESA)


Planetary conjunction

As the planets dance around the Sun in their orbits, from time to time two or more planets will appear to approach each other, drawing closer over days before separating again.  These events are called planetary conjunctions, and are tricks of our earthbound perspective; the planets are still separated by millions of kilometres.

A popular explanation of the Star is that instead of being a single object it was actually a conjunction of Jupiter and Saturn that occurred in 7 B.C. in the constellation of Pisces.  This speculation goes back at least as long ago as the 13th century, but it was Johannes Kepler who was the first to argue this in depth in a tract published in 1606. The conjunction of 7BC  was a rare “triple conjunction” when there were three separate close encounters of the two planets seen from Earth.  In astrology, the constellation of Pisces apparently symbolises Jewishness, so the theory goes the Magi would have seen this as revealing an event important to Jews.

However would appear unlike anything described in the Bible. Each of the three conjunctions lasted only a few days, yet the the Star guided the Magi through a journey of several weeks at the very least.

Note too, that a much closer, and hence more startling, conjunction of the same two planets occurred in 66 BC. Arthur C. Clarke suggested that this earlier meeting of the planets “should have brought a delegation of wise men to Bethlehem sixty years too soon!”


Image of Celestial_Conjunction_at_Paranal

Conjunctions are striking sights. In the night sky over ESO’s Very Large Telescope (VLT) observatory in Chile, the Moon shines along with two bright companions: already aloft in the heavens and glowing in the centre of the image is Venus, Earth’s closest planetary neighbour, and, to its right, the giant, though more distant planet, Jupiter. (image credit: ESO/Y. Beletsky)



A nova is a titanic nuclear explosion occurring across the surface of a white dwarf. This happens if the white dwarf (the dead but still white hot core of a dead star) has a nearby companion star. The white dwarf can leech material, including hydrogen, like a vampire from its stellar partner. Eventually the hot and compressed hydrogen coating the surface of the white dwarf ignites in a runaway nuclear fusion reaction. The release of energy is staggering; the star system brightens ten thousandfold in mere hours.  Often the star system where the explosion occurs has been overlooked by astronomers, the sudden flare of light reveals its existence, as though a new star had leapt into being (hence the term ‘nova’, being ‘new’).

Astronomers discover about 10 novae every year in the Milky Way, but there are probably many more occurring. It is not impossible that the Star was a nova, but if so it would have blazed gloriously in the night skies across the Earth. Why was it not then recorded in the annals of ancient China? (Some astronomers, notably David Hughes, have suggested that the comet of 5BC in the Chinese archives was actually a nova rather than a comet, but this theory has not been widely accepted.)


Not to be confused with a nova, a supernova is a still vaster nuclear explosion centred on a star which usually utterly destroys the star. Some are caused by the same process as leads to an “ordinary” nova- except the white dwarf is torn apart in the final paroxysm. Alternatively we may witnessing the suicide of two white dwarfs colliding and being annihilated in the process. Another known form of supernova occurs when an old and gigantic star reaches the end of its life. Its core will implode, followed almost instantly by a colossal nuclear explosion. For a few weeks the dying star will outshine all the other stars in the Galaxy combined! One of nature’s most spectacular events, supernovae are rare, occurring perhaps about once or twice a century in the Milky Way. No “naked eye” supernovae have been observed in our own galaxy since Kepler’s Supernova seen in 1604, although supernova SN 1987A in the Large Magellanic Cloud reached 3rd Magnitude despite its vast distance of 170 000 light years from us.

A “nearby” supernova would be a stunning sight in the sky. At its peak,  Kepler’s Supernova was brighter at its peak than any other planet or star in the night sky and was visible in the blue of the daytime sky for over three weeks. Yet there is no evidence for such a supernova. Apart from the continuing silence from the Chinese annals there are no known supernova remnants from two thousand years ago,

As you can, the identity of the Christmas Star is still mysterious. No phenomenon known to astronomy truly seems to match it. I am sure stargazers will continue to debate this enigma as long as Christmas is celebrated.

(Article by Colin Johnston, Science Education Director)