﻿ The Christmas Star: Planetarium

What was the Star of Bethelehem?

23 December, 2010

Comet Siding Spring
Image of comet Siding Spring. Comets are often suggested as the 'Star of Bethelehm' but they are unlikely to be a candidate.
Image: NASA
Source: NASA

During the festive season astronomers are often asked about the story of the ’Star of Bethlehem’ in the Christian Bible: Was it real? What could it have been? We cannot know the answer to the first question. It is possible the story is a later invention, made up in order to fulfil a prophecy. But even if this is the case it is interesting to consider why the story was important, what it may have meant.

Two common suggestions are that perhaps it refers to a comet or a supernova. These are two kinds of astronomical object that can suddenly appear bright in the night sky.

Comets have been regarded in many cultures as being potent omens. However almost universally they foretold doom, whereas the Magi, or “wise men” who saw the star expected it to show something good.

Supernovae are stars that explode suddenly as they die, releasing enormous amounts of light and appearing in our skies as a new bright star. The astronomer Johannes Kepler saw a supernova in 1604 and soon after suggested that the ’Star of Bethlehem’ might have been a supernova. But Chinese astronomers of the time kept careful records of supernovae, and there is none that matches in timing.

Comets, supernovae and other astronomical objects also have another problem: they move across the sky through the course of a night. The gospel suggests that the ‘Star’ was first seen in the eastern sky, yet it led the Magi to travel westward. How can a moving object provide this kind of guidance?

This question suggests a different kind of explanation. It may have been that what was important was not the location in the sky, but the position on an astrological chart. Scientists no longer consider astrology a science, but in ancient times astronomy and astrology were inseparable. The Magi were Zoroastrian priests (not kings) who were careful observers of the sky and practitioners of astrology. In their system the sign of Aries was associated with Judea, so it may have been this that led them to Jerusalem.

Three events that have been considered are a close conjunction of Jupiter and Venus in 2 BCE, a massing of Jupiter, Saturn and Venus in 7 BCE, and a pair of occultations of Jupiter by the Moon in 6 BCE.

A conjunction is when two planets appear near each other in the sky. In 2 BCE Jupiter and Venus appeared so close that they appeared as a single bright star. This event occurs too late for the commonly accepted date range for Jesus’ birth, but if the story is a later creation it might refer to a memory of this event.

A massing of the planets is when more than two planets appear near each other in the sky. Conjunctions of two planets are relatively common but a massing of three planets is much rarer so would have been of more interest.

An occultation by the Moon happens when a planet like Jupiter appears to pass directly behind the Moon as seen from Earth. This happens quite rarely and so is an unusual event. Unfortunately the occultations would have been very difficult to observe and so it is doubtful whether the Magi actually saw these events.

So while there are certainly difficulties for the astrological interpretation of the ’Star of Bethlehem’ it is quite likely that this is the kind of event these skywatchers were interested in. Fortunately in modern times astronomers no longer have to worry about the astrological significance of celestial events!

Comments (6)

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Mary K. Themis 9 February, 2011 13:32
I love the planets and galaxies and would dearly love to be able to walk among them in a 3D atmopherics type room like on Escape to Witch mountain with Dwayne Johnson the Rock and Seth and Sarah that was so real looking
Paul (Howard) 9 May, 2011 09:52
So is the current early morning planet event a 'conjunction' - is it rare for 4 planets to rise so close together ? thanks - great info on your site - Paul
John Kell 20 May, 2011 16:27
The aligning of planets focuses minds! Is there a site that shows the locations of the planets on a PLAN view, instead of the SECTIONAL view we have from Earth all the time?
Discovery Centre 29 May, 2011 11:52

Hello John, yes there is indeed a website that shows that information, you can find it at http://www.heavens-above.com/planets.aspx?lat=0&lng=0&loc=Unspecified&alt=0&tz=CET . Look for the link marked “Solar System Chart”. You can also enter any date into the chart.

Hope this helps!

Jason 9 November, 2011 16:59
is the planetarium dome 16 or 60 metres tall ?
Discovery Centre 11 November, 2011 12:07

Hello Jason,

The Planetarium has a 16 metre diameter dome, which means that it is about 8 metres high at the centre when looking up from inside.

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