Astronomers and the star of Bethlehem

The remains of a stellar explosion that appear in Earth's sky in 1604.

An X-ray view of the remnant left behind by Kepler’s supernova of 1604. The different colours indicate different energies of X-rays, while the background stars are from the Digitised Star Survey. Courtesy X-ray: NASA/CXC/NCSU/M.Burkey et al.; optical: DSS

This time of the year it is appropriate to contemplate the star of Bethlehem that is briefly mentioned in the in the New Testament’s Gospel of Matthew. Over the years astronomers have engaged in considerable speculation on what the star may have been, putting aside any considerations on whether it was meant to be purely miraculous or a rare, but natural phenomenon. With little description given – if it had been described as a hairy star we would know that it was a comet or if it had been described as new star we would know it was a nova or a supernova – there is scope for a wide range of suggestions: comet, nova, supernova, planetary conjunction and more.

Here we will mention just two of the theories that astronomers have suggested to account for the star. We will start with that of the late 16th/early 17th century German astronomer Johannes Kepler and then follow with Michael Molnar’s recent exposition that is regarded as a game-changer in tackling the problem.

In the autumn of 1604 European astronomers and astrologers were all carefully watching as the planets Jupiter, Saturn and Mars bunched close together in the sky. Kepler, observing from Prague, missed both the conjunction of Mars with Jupiter on 26 September and the conjunction of Mars with Jupiter on 9 October due to cloud. However, the day after the Mars-Jupiter conjunction a friend of Kepler saw a bright new star near Jupiter that Kepler himself saw a week later. He studied it diligently as it faded over the course of the next year and wrote up his observation in a book published in 1606. Of course, Kepler had no idea what he called the “Nova Stella” could have been; today we know that it was a supernova or exploding star and so far the last to be seen in our own galaxy.

From his observations Kepler drew the conclusion that important planetary conjunctions could be the precursors of the appearance of a new star. He calculated that there was a Saturn and Jupiter conjunction in June 7 BC and proposed that that was the time the star of Bethlehem appeared. He considered what this star may have been like and concluded that it “was not of the ordinary run of comets or new stars, but by a special miracle moved in the lower layer of the atmosphere”.

Not much credibility can be given to Kepler’s suggestion, but the work of Michael Molnar published as a book in 1999 has been treated most seriously by scholars. Molnar says that we should look for an event that astrologers of the time would have regarded as significant and not for phenomena such as novae or supernovae that modern astronomers would find of interest. As a first step Molnar deciphers the text describing that the star was seen “in the east” as meaning a heliacal rising, which is when a planet or star can be first seen in the dawn sky after a period of being too near the Sun.

In a complex discussion Molnar establishes the event as the heliacal rising of Jupiter on 17 April 6 BC, when Jupiter also approached the crescent Moon. Although the crescent Moon was too thin and too close to the Sun to be seen, according to Molnar that made no difference as the astrologers of the time could calculate that the event happened and that was sufficient for them.

The conclusion that the star of Bethlehem was an unobservable celestial event is somewhat unsatisfactory and Molnar may not be right in his choice of event. However, his idea of thinking about the star on the basis of the astrology of the time instead of the view point of contemporary astronomy represent a shift in attitude that is likely to be followed by future scholars. That these future scholars will ever come up with a definitive answer seems unlikely, but like the astronomers so far, they will have fun trying.

W. Burke-Gaffney, SJ, “Kepler and the star of Bethlehem”, Journal of the Royal Astronomical Society of Canada, Volume 31, pp 417-425 (1937)

Michael Hoskin, David W. Hughes and J. Neville Birdsall, Review Symposium “The star of Bethlehem”, Journal of the History of Astronomy, volume 33, pp 386-394 (2002)

Michael R Molnar, “The star of Bethlehem: the legacy of the Magi”, Rutgers University Press, New Brunswick and London (1999)


6 responses to “Astronomers and the star of Bethlehem

  • The original article from the Observatory got on the right track suggesting the solution to the mystery was probably more astrological than astronomical. I agreed and because I believe one can even make an overwhelming case for that. It was however suggested the astrological argument would be hard to prove. The latest comments here, ignoring what I contributed, send the matter backwards. Why? How?

    Just as by tradition comets were taken as harbingers of bad events (and thus something like Halley’s Comet could never be symbol of “tidings of great joy”), so likewise the fixed stars are mostly deemed negative (malefic) in astrology.. Especially a fixed star associated with the worst punishment of the ancient world is not a symbol of joy!

    But because the astrology I am pointing to really, however inconveniently for scientists consistently signs and works in this case, sure enough the ancient mathematical formula “The Part of Death” in Jesus’ horoscope is at 14.44 Libra conjunct Acrux at 14.13 Libra. As though that itself doesn’t open the possibility of death by crucifixion, the point is driven home (astrologically) by the way these two points conjunct Mercury at 13.54 Libra, Mercury being the chart “ruler” for Jesus since Gemini rises, and a chart ruler will always be connected to the body. So this person’s body could well go to a cross.

    Oh all mumbo jumbo, too fanciful!…I know the responses of those who’ve never looked into these things and for whom they must, without even testing, be false and beneath consideration. But do you want the truth or not? I would insist the chart of Christ fits again and again exactly as a fingerprint and works to this day for Jesus issues as dramatically shown in the feature article of my blog following the poem. The originator of the Acrux theory talks of the Jesus’ “myth”. And that’s the point. It’s myth is either sought for or arbitrarily assumed, not a real historical person or real Magi using certain known techniques. Almost amusingly the article on the Acrux theory speaks of the archetypal. What’s archetypal in this whole business whether two millennia ago or today is “no room at the inn” as my poem stresses!

  • The Star of Bethlehem could have been Acrux from the Southern Cross. Consider this star and everything will fall into place, like finding the correct piece in a jigsaw puzzle.

    The Southern Cross can not be seen from Jerusalem today, but 2000 years ago all of the constellation was visibile in the southern sky. It would have been visible only a few weeks each year – rising in the east and moving west until the break of dawn. The lowest star just above the horizon was Acrux. Astronomers of the time may have noticed from records that the star Acrux was slowly disappearing from view and that it was now below the horizon. This would prompt some to travel to mountains (near Jerusalem) to gain a better view, and then to continue south (past Bethlehem).
    Bethlehem is directly south of Jerusalem, and would be an obvious landmark for observations of a star that was just above the horizon to the south.

    The mystery of the Bethlehem Star came about because of a misunderstanding between the astronomers describing Acrux empirically, and the people in Herod’s Court who took the description culturally – without identifying the star being pointed out by the Magi. The story evolved into the famous myth over the next 80 years.

    For more about Acrux as the possible star of Bethlehem, see the page at

    • Hello Robert. An interesting suggestion, but you have work to do on the astronomical part of your suggestion. Your website states: “2. The Magi were observing the helical rising of Acrux from the vantage point of Jerusalem. 3. The star rose to the east and was last visible at dawn as it was just above Bethlehem to the south.” If you check out the definition of a heliacal rising you will find that the star is only visible for a brief moment just above the eastern horizon before dawn arrives and blots the stars from the sky. At heliacal rising Acrux would have been seen low in the south-south-east and could not have been followed towards the south.

      • > Hello Nick,
        Thank you for looking into this seriously.
        When I researched this, there was a window of about two weeks when Acrux would have been visible in the southern sky from Jerusalem, about 2000 years ago.
        Looking back, and projecting our current calendar back to those days, the relevant time would have been around the middle to end of November / early December. The 24th of December is right on the tail end of that window – as you point out above.
        But there are a few days when Acrux would be seen rising to the east, moving west just above the horizon, and then it Stopped being visible after sunrise while it was right above Bethlehem.

  • You’ve said it….The astrological direction is the one in which inquiry will or needs to go, but I am prepared to claim as a doctor of religious studies, theologian and qualified astrologer I know beyond a shadow of doubt I have the solution and can prove it as much as that will ever be possible especially to the non astrologer. See this month’s blog “The Magi at Era’s End” at the above address.

    Especially as my claims are remarkable with implications for many things you may ask why doesn’t anyone know? Why weren’t they published when a top editor of a leading publisher declared my work on this to be fascinating, ground breaking and publishable? There are various reasons, but I suggest that one is the main spokesman for the theory I have so radically developed, astronomer David Hughes, has never contacted or acknowledged me in over 20 years despite his publisher, the Society of Authors, one of my editors who knew him personally, asking him to contact me, while my own emails (which have long ago stopped), have never got anywhere with him either. Obviously his support would have encouraged examination of my claims not least by media on which Hughes regularly expresses his views on the Bethlehem Star..

    Anyway you can see my blog which starts with a poem on the subject, and if you have any questions, feel free to ask me.
    Rollan McCleary (Dr)

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