The Star of Bethlehem - an Astronomers Perspective

By Paul Hannah ~

Every year articles appear in the mainstream press and magazines speculating on the 'real' explanation for the Star of Bethlehem. Given our modern understanding of astronomy, there are a number of candidates which have been given to explain the phenomenon and fit the Bible story. However, even if the ideal star or astronomical object could be found there are serious practical problems with taking the story on face value.

The Bible gives the story as follows:

Now when Jesus was born in Bethlehem of Judaea 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 then: Lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was. – Matthew 2:1-12

The astronomical elements of the story are: The Wise Men came from the east, they saw a 'star' in the east, they followed it and it stood stationary over the stable.

The 'Wise men", also known as 'Magi' are located by a number of traditions and historians to come from Media in Persia, modern day Iran, a place to the east of Bethlehem. These men were probably astronomers and astrologers (at that time the two occupations were interchangeable) so we can assume that they were at least familiar with the night sky and the motion of stars and planets.

Stars appear to rotate in the sky around the north and south celestial poles. Those closer to the poles describe a circle in the sky and are called circumpolar, the ones closer to the equator only describe an arc.

At the latitude of Persia non-circumpolar stars rise in the east, trace an arc over the southern sky and then set in the west. If the Magi followed an ordinary non-circumpolar star as it moved across the sky, they would walk in ever widening circles, which may after a long journey have ended up in Bethlehem, but it is unlikely. Or they could have picked a time, noted the direction of the star and travelled that direction and reaffirmed the direction each night at the same time. Or the Bible could be literally true and the star could have just stayed in one spot in the sky to be followed From Persia (or anywhere east of Bethlehem).

To get to Bethlehem from Persia, the Magi needed to travel west and yet the Bible clearly says the star was in the east. If our three *wise* men travelled to Bethlehem from Persia by going in the direction of the star, it would require a circumnavigation of the world through China, across the Pacific, North America, Europe and finally the Middle East. Not the route we'd consider today, even if we didn't have to rely on camels and horses. If the star was circumpolar, the Magi would have travelled roughly north, not west, in which case they could never arrive at Bethlehem as the closer they travelled to the north pole, the more circular their route.

For a star to appear to remain 'fixed' in the sky it must counter the rotation of the Earth – it would have to move relative to the other stars in the sky and follow the Earth as it rotates on its axis. Einstein would have a problem with this. The Earth rotates at the latitude of Bethlehem at about 1400 kph, for a star to appear stationary it must rotate around the earth at that relative speed. But the further away from Earth the star was, the greater the arc it traces through space and the faster it must travel to appear to maintain its position. If the star was any further than around 4 billion km from earth it would be travelling at beyond the universal speed limit, the speed of light. This trajectory would place the star inside the orbit of Pluto. Stars in their light emitting stages of life come in many sizes, from thousands of times larger than our sun (eg VY Canis Majoris) to red dwarfs one of which (OGLE-TR-122b) has been measured to just a little larger than Jupiter. A star of any visible size this close to earth, even a red dwarf would be of interest to more than a couple of Persians. We would expect at the very least the Chinese astronomers to have recorded it but there is no other record anywhere of such an event. As Bethlehem is not on the equator, the star would not be technically in a geosynchronous orbit, that is, not in orbit around the centre of the Earth, rather it would be orbiting some point between the centre and the north pole. At any distances required for the respective gravitational fields to interact, it would not be our little Earth that called the shots - although technically we know from Newton that bodies orbit around a point between each other, the star would be dominant and we would appear to orbit it. Irrespective of this, such a body, suddenly appearing inside our solar system, would affect the planets and even our sun, probably catastrophically.

Could it have been a 'wandering star' passing through our Solar System?

It strains credulity to imagine a star passing through the solar system as close as it would have to be without disturbing the orbits of our own or any other planet. If this is the explanation, surely more than a handful of people would have noticed? If it was a 'wandering star' where is it now? It could only be less than 2022 light years away, easily visible to modern astronomers. No such 'wandering star' is known.

What about a conjunction of planets or stars or of planets and stars?

The same problems of real versus apparent motion (or lack of it) apply, plus each object would have differing orbits giving different apparent speeds across the sky. Consequently conjunctions don't last very long, far shorter than it takes to drive from Baghdad to Bethlehem let alone ride a horse or camel.

Further, even if an object, let's call it a star, could point the way somewhere, it could only point a line between it and the observer. Travelling along that line could give you the direction to take but no indication of the point to stop along the line. For example, if the star shone in the sky seemingly above a stable then how would they know it was that stable and not the hundreds that lay beyond? The fact is they couldn't. Take a look at any star tonight. It may appear to be above a tree (or a house or a rock) but if you walk beyond that tree then the star is above something else. There can be no indication, just from that star, of distance from the observer.

Consequently our Magi, if they followed a star in the east, would travel in the wrong direction, possibly in circles and with no idea where to stop. That they got to Bethlehem in their lifetime, would be amazing enough, but to find a particular stable and know to stop there, must have truly been a miracle. And anyway, if the Magi could follow a star to the stable, why did they stop and ask Herod for directions. Asking a Bronze Age king where the baby is that will replace him was an incredibly stupid thing to do. What else would Herod do, but kill all the babies? And to save all that unnecessary slaughter of the innocents, couldn't god have told them (in a dream or something) to stay away from sociopathic kings?

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