The Star of Bethlehem is one of the most enduring symbols of the Christmas story. This is perhaps surprising because it is only referred to in one of the gospels, the gospel of Matthew, and in only 3 verses of it. So if any part of the Christmas story has to be an add-on, a later accretion, surely this is it. Wouldn't it be nice to mark or herald the arrival of God's Son, the incarnation, with a celestial, an astronomical wonder? But we can also say that if any part of the Christmas story is susceptible to scientific questioning, this is it. After all, an astronomical phenomenon is described. Did one occur at about the right time?

At home we don't finally throw away Christmas cards until the Christmas after. When sending cards it helps, it's nice to look back to see from whom we received them the previous year. The other day I analyzed last year's lot and out of 68 cards some 26, or rather more than one-third, featured directly or indirectly a star.

Let me remind you of the verses in Matthew's gospel which refer to the star, and as you will recall it is the Magi's arrival in Jerusalem that caused the flurry of interest about it:

“Where is the one born to be King of the Jews? We saw his star in the east and have come to worship him.”

“After they heard the king, they went on their way, and the star they had seen in the east went ahead of them until it stopped over the place where the child was. When they saw the star they were overjoyed.”

Concerning the star, unlike the Virgin Birth and the puzzle over Quirinius, we have an opportunity to do what scientists like to do which is repeat the experiment, or at least look for hard evidence of something happening. One can compute back the motions of planets, look for the debris of exploding stars, novae and supernova, investigate records or observations of unusual sightings such as comets and so on. However, we have a tall order from Matthew's account because it doesn't just say 'a star' appeared when Jesus was born: no, some very precise facts of both time and space are spelt out or can be inferred.

Facts about the star of Bethlehem:

  1. It was a new star (at a point in time it appeared, the Magi saw it, and saw it as new).
  2. It was a star that continued for sometime or reappeared a little later, and then disappeared (the Magi excitedly tell Herod about the timing and when it first appeared).
  3. The star was first to be found in the eastern sky and then by inference in the sky to the south (when the Magi set out from Jerusalem to go to Bethlehem their road went almost due south).
  4. The Magi were very excited about seeing the star again after their meeting with Herod.
  5. The star by implication was pretty bright and impressive to make three wise men travel hundreds of miles, and all Jerusalem were excited by it and the Magi's visit.

To meet the criteria set down in Matthew's account we need a bright celestial object that appeared only for a time - or appeared twice - and which moved its position from east to south in the sky. Well, three phenomena have been proposed as explanations:

  1. A conjunction of planets, particularly Jupiter and Saturn. A conjunction is when the planets as seen from earth appear to overlap in the sky and their light coalesce and become increasing brilliant. After Venus, Jupiter is the brightest of planets - you can see in the night sky now - and if Saturn's light was added, and Saturn is like a bright star of magnitude 1, truly a bright spectacle would occur. Such an event only occurs once every 900 years or so, it is pretty rare. What is interesting is that such a conjunction did actually occur and occur 3 times in the constellation of Pisces in the year 7 BC.
  2. The second phenomenon is an exploding star, a nova or supernova, which appears brilliant for a time before fading - Foucquet suggested this explanation as long ago as 1729.
  3. The third possibility is a comet. In our times comets have not been seen often nor as very bright though Hale-Bopp in April this year tried to impress and you could see it with the naked eye at night. Compared with the comets of previous centuries, including the famous appearance of Halleys every 76 years, we are bereft. Several comets in Victorian times and earlier appearances of Halley's comet were often so bright as to be visible in full daylight - that is something I've not experienced.

Intimately associated with the story are the Magi. (And by the way they are not Kings, despite the carol 'We three kings of orient are'. The gifts they carried were not signs of their status, but were being brought to one as befitted royalty, they were bringing gifts to give to one who is of kingly status). You recall their question "Where is one born King of the Jews?".

What is known about Magi? (At this point I should emphasise that much of what I will cover arises from work by Professor Colin Humphreys, Professor of Materials Science at the University of Cambridge and, in particular, a paper he wrote on the subject of the Star in 1993. I've also read quite widely about the astronomy of the star, but it is Colin Humphreys' analysis which is so thorough and so impressive.) To return to the Magi, they were the ones the Bible says alerted everyone to the significance of the Star so what is known about them?

There are many references to Magi in ancient literature. Some were even known to have visited Herod before, probably in 10 BC. People were familiar with them coming and going, visiting Kings and Emperors such as to Nero in 66 AD. They concerned themselves with 'timely signs and coming events' writes Philo of Alexandria in the 1st Century through being students of astronomy and generally interested in interpreting dreams, divination, astrology and so. And they probably came from the region of Babylon in Saudi Arabia (or possibly Iran since Magi were originally a religious caste among the Persians). If, as is likely, they came from Babylon, it is important because this is where the Jews were in exile 500 years before. Because of this 70 years period of exile Babylonian scholars would have become familiar with Jewish prophecies of a Messiah and the later Magi would almost certainly have known about it.

So we have this picture of wise, scholarly men keen to interpret signs and events, careful observers of the sky and intimately interested in astronomy, willing to take their wisdom to the known world's leaders, and knowledgeable about prophecies including that of the Jews. - seen stars, will travel!!

Last week we concluded that Jesus was born about 5 BC, and certainly before the death of King Herod in the spring of 4 BC. And so it is reasonable to ask can astronomy tell us what celestial events occurred about this time. This is what we will now concentrate on.

  1. I've already mentioned the rare series of conjunctions of Jupiter and Saturn occurring in 7 BC. Astronomers calculate they occurred in the months of May, October and December. Several authors have written about this unusual event and sought to relate the first sighting by the Magi as the May conjunction and the later conjunctions in October and December as explaining the account of Matthew 2. 9-10 and giving the Magi time to journey the many hundreds of miles from Babylon to Jerusalem. Indeed, many years ago I myself actually gave a talk suggesting this as a possible explanation for the star - it is an appealing explanation and there is absolutely no doubt that the Magi saw these conjunctions as would everyone else living at the time. But 7 BC is really a little early.
  2. Now interestingly another rare astronomical phenomenon occurred in 6 BC. The three planets Jupiter, Saturn and Mars appeared very close together in the sky for a time - by the way Mars in the night sky is brighter than Saturn but not as bright as Jupiter and looks reddish - and this is known as a massing of the planets. They were massed again in the constellation of Pisces. This event only happens once in 800 years, occurring last in 1604 AD. 6 BC is still an early date and a massing or grouping of planets doesn't correlate with the account of a star as we have in Matthew. Nevertheless we do have two remarkable and rare astronomical phenomena occurring in successive years 7 BC and 6 BC.
  3. Data about exploding stars, the nova or supernova, are more difficult to establish and by nature they are ephemeral flaring up and then receding in brightness. Sometimes supernovae leave a nebula or cloud of gas that continues for centuries and can be seen through powerful telescopes. But being stars they don't move in position in the sky and so would fail to meet one of the requirements of Matthew's' account. (At this point I should add that planets have that name because in Greek this means 'wanderer' because they move in position against the backdrop of 'fixed' stars - thus planetary movement could satisfy the star of Bethlehem being in the east and then in the south).
  4. That leaves us with what has been the oldest explanation, was the star a comet? This is what was claimed by Origen in the third century, but the difficulty with comets is that by no means all appear at regular intervals. Halley's, as we all know, orbits every 76 years, but some appear and then disappear off into space with enormously long return times and beyond observational reach - in effect never to be seen again. So how can we know if a comet appeared? Indeed, what records of astronomical events do we have, in contrast to the computing back of planetary movements. We have to go 8000 miles east for the best records - the Chinese assiduously recorded such events as far back as 2000 BC and Professor Humphreys in his 1993 paper publishes an extract of a table showing what comets and novae were recorded by Chinese astronomers from 20 BC to 10 AD:
The table lists three comets beginning with Halley's of 12 BC and two further comets in 5 BC and 4 BC.
Ho Peng-Yoke Catalogue No. Date (Julian Calendar) Description
61 26th August 12 BC (for 56 days - Halley's comet) po (comet)
63 9th Mar - 6th April 5 BC (for over 70 days) sui (tailed comet)
64 April 4 BC po (comet)

It is the 5 BC comet which is exciting because the internal evidence from the Chinese observations, the official records of the Han dynasty, suggests it first appeared in March/April in the star constellation of Capricornus (the horned goat) which would be in the east. Now comets are like planets they do move across the backdrop of stars - you will remember how the sightings of Hale-Bopp changed between March and May - and they move about 1-20 per day. The records indicated that the 5 BC comet lasted over 70 days before fading and in this time it would have moved across the sky from east to the south and shift of about 90+0. So in the sky, brilliantly visible across the world and certainly from Jerusalem, appeared a comet in the spring of 5 BC. Was this the star of Bethlehem?

In the table you will note that the type of comet is described as having a tail. Some tails of comets are impressively long for a time, but comet shape changes as seen from earth as they move towards the sun, swing behind it, then out and away again. So was this comet, with its long tail, what the Magi saw and rejoiced over? Well we have one more clue that it might be. In Matthew, the writer uses the expression in the NIV of the Star 'stopping over (Bethlehem) the place where he lay'. The King James version translates this as 'stood over'. Now the interesting point is that precisely this expression is used by Dio Cassius to describe the appearance of Halley's comet in 12 BC which appeared before the death of Marcus Agrippa '. . . stood for several days over the city (Rome),' and again Josephus describes a star resembling a sword (the next return of Halley's comet) in 64 AD which is said to have 'stood over' Jerusalem. Tacitus also refers to this particular comet. So Matthew's unusual expression about the star 'stopping' or 'stood over' strongly suggests he is referring to a comet. And we know that there was a bright comet in the sky at the likely time of Jesus' birth.

So let me begin to suggest a chronology, a sequence of events that plausibly happened. And this is the chronology that Professor Humphreys proposes.

In 7 BC and then 6 BC the Magi would have observed and been greatly impressed by the astonishingly rare planetary events - conjunctions followed by a massing. They were for them great portents. And then in the spring of 5 BC a comet appears in the eastern sky - now remember these are facts, these astronomical events happened - signifying to them that some great event was imminent. The comet appeared in the east in the constellation Capricornus - and had the Magi remembered Daniel's prophecy concerning the goat and its powerful horn - and this set the Magi to journey to Jerusalem, probably taking 40-50 days by camel following the 900 mile route along the fertile crescent. They are unlikely to have taken the shortest route of 550 miles cutting across the desert. And so 6-8 weeks after the comet appeared in early March they arrive in Jerusalem and ask the astonishing question to the King 'Where is the one born to be King of the Jews? We have seen his star in the east.' And, as Matthew's gospel tells us, all Jerusalem got excited - Magi visiting, asking questions about a new and mighty King whose coming was announced they said by the bright comet they could all see, Herod meets with them secretly and learns about the remarkable coincidence and rarity of the astronomical events of the last 2 years, the conjunctions, the planetary massings, and now the bright comet, and so on. You can imagine the Sunday Press: 'Uproar over comet'; 'Herod faces rival', 'Leak of Magis' secret'. Anyway the authorities are summoned - the chief priests and the pharisees - and are consulted as to where the Messiah is to be born and they cite Bethlehem from Micah's famous prophecy (Micah 5:2) that Matthew repeats:

“But you Bethlehem, in the land of Judah, are by no means least among the rulers of Judah; for out of you will come a ruler who will be the shepherd of my people Israel.”

And here we come to the climax. The Magi did not know about Bethlehem, else why ask the question. They could inform Herod and his court about astronomy but the detail of where the Messiah (Christ) would be born appears unknown to them. They learn it is Bethlehem and they set out and as they leave, perhaps by the Essene gate of Jerusalem and gaze out over the Hinnom valley, there ablaze before them, precisely ahead of them on their last days journey - the 5 miles to Bethlehem - is their comet, because Bethlehem is south of Jerusalem. They were right, their comet stood over the town where long ago the birth of the Messiah was predicted. They had gone to the capital, to Jerusalem, and from the capital the direction they were told to go was exactly towards the comet as it stood over the town. Of all possible directions of N, of E, of W it was S they go. No wonder then, Matthew 2 verse 10 describes the Magi as being overjoyed at seeing the star again and no wonder tradition has it that the star guided them! Perhaps we would not say it was the star, but Scripture the true guide!

The comet of 5 BC is a very satisfactory explanation for the star of Bethlehem. It explains the events of Matthew's record. We cannot be absolutely sure of course, but we do know that there appears to have been a brilliant comet in the sky at the likely of time of Jesus's birth. And we have an interesting piece of corroborative evidence about the sequence of events. When Herod ordered the appalling massacre of all boys 2 years and under in and around Bethlehem, did he chose 2 years of age to cover all babies born since 7 BC when these portentous astronomical events began happening? Herod certainly met with the Magi in secret and would have learned when these momentous events began, so his 2 years of age was to make sure he covered the whole period he thought possible.

We have then an adequate explanation. One that affirms the historicity of Matthew's gospel. A brilliant comet stood over Bethlehem in late Spring of 5 BC. This further confirms the year and approximate time, as we learnt from Luke last week, as the probable date of Jesus's birth. We know Christmas is not right, only being celebrated in what we call late December from the 4th Century AD and Christians adopted it by replacing a pagan festival of the winter solstice - longest night, shortest day. So if Jesus was born in the Spring of 5 BC, and the comet appeared for about 70 days from mid March to late May - this precisely covers the Jewish Passover festival. Did Mary and Joseph come to Bethlehem to register for the Census and attend the Passover celebrations as well. It would help explain why all the accommodation was taken. Certainly we know that Jerusalem and the surrounding towns and villages were crowded with people coming to register for the census and perhaps up for the passover too - there was no room in the inn for Mary and Joseph - 'no room in the inn' how it haunts one!

This is all complete speculation, but let me press Scripture even more, and particularly the interesting term in John's gospel of calling Jesus the 'Lamb of God'. Was the Lamb of God born on the very day lambs, pure and without blemish, were selected for the Jewish Passover sacrifice? Or perhaps 4 days later when such lambs were actually sacrificed? There would be a symmetry, a perfection, a solemn symbolism about such a date if true for what Christians believe - as Dorothy Sayer entitled her play 'The one born to die'. If yes, then Jesus was born on the night of 14th April or 19th of April 5 BC. But this is speculation.

To parody again Stephen Hawking's turn of phrase, which really rather appeals to me, but this time with a singular difference: 'We may know how the star appeared, but why is to know the mind of God.' The crucial and singular difference is that God has revealed why, He has revealed his mind to us. In the verses that immediately precede the account of the star we are told the one who is born is called "Immanuel - God with us", and his name will be Jesus "because he will save his people from their sins." That is what was in the mind of God for the good of us all - the gospel.

Thank you for listening so patiently. And may I wish you all a very happy Christmas.

Julian Evans
Originally given as one of a series of talks in December 1997
Reference: Humphreys, C. (1993) The Star of Bethlehem.
Science and Christian Belief 5 (2), 83-101