Possible
Explanations of the Star of Bethlehem
The are many
possible explanations of the Star of Bethlehem which have received wide support
over the years. The most widely accepted are variations on comets, novae and
conjunctions, although a new candidate, which has to be taken seriously, is the
idea of a planetary occultation. What are these candidates and what are their
strengths and weaknesses in each case?
Planetary
conjunctions
The idea that a planetary
conjunction might have been the Star of Bethlehem is usually credited,
erroneously, to Johannes Kepler. In fact, the planetary conjunction theory only
dates back to the middle of the 19th Century. Kepler only pointed
out that a conjunction of Jupiter and Saturn had occurred near the time of the
Nativity whilst himself favouring the nova/supernova hypothesis. A planetary
conjunction is when two (or more) planets approach each other in the sky, one
passing due south of the other. Conjunctions can be quite spectacular and last
for several nights although a really compact conjunction lasts for just a few
hours.
It was in 1968 when Roger
Sinnott wrote a highly influential article in Sky and Telescope pointing to the
June 17th 2 BC conjunction of Venus and Jupiter as having been
particularly spectacular from Babylon that this theory took off. Sinnott’s work
is still one of the finest ever carried out in this field and all the more
laudable for having been done from planetary tables, without the assistance of
a computer. Sinnott investigated conjunctions over a wide range of dates from
12 BC to 7 AD finding more than 200 conjunctions of the major planets. He also
found no less than 20 compact groupings of three or four planets, of which only
4 would have been observable. After carefully filtering the events, Sinnott
concluded that the 2 BC conjunction, in Leo, would have fitted the bill.
On June 17th 2
BC, as seen from Babylon, Venus and Jupiter would have set 3 hours after
sunset, with the two planets too close together to separate by eye, having
closed considerably in the time since sunset. In fact, we now know that the
disk of Venus actually passed in front of Jupiter, occulting it partially.
The problem with
conjunction though is that they are too common. When the Magi have been waiting
several hundred years for the birth of the Messiah, they would have seen all
kinds of occultations and it is hard to believe that a single occultation,
however spectacular, could have been the Star of Bethlehem, quite apart from
the fact that this one happened several years too late.
A Triple
Conjunction
Any pair of superior
planets (that is, planets outside the Earth’s orbit) can give rise to a triple
conjunction whereby, instead of a single pass, the planets meet and separate
three times over a period of a few months. The more exterior a pair of planets
are, the more frequent are triple conjunctions relative to normal conjunctions,
although the more infrequently a conjunction of any kind will occur.
Jupiter and Saturn will
enter conjunction about every 20 years. During the last millennium BC, however,
no less than 7 triple conjunctions also took place – one every 140 years, on
average – although the interval varied from 40 years (as between 861 and 821 BC
and again between 563 and 523 BC) to 377 years (as between 523 BC and 146 BC). Over
the millennium there were 43 "normal" conjunctions between the two
planets and 7 "triple" conjunctions.
In December 1603 Johannes
Kepler observed a conjunction of Jupiter and Saturn (a normal one), followed by
a massing of Jupiter, Saturn and Mars, when all three planets were close
together in the sky. He calculated that a similar set of circumstances would
have occurred in 7 BC. In fact, the 7 BC conjunction was a triple conjunction,
although Jupiter and Saturn were never much less than a degree apart.
In 1976 David Hughes
popularised this triple conjunction and suggested that it might explain the
Star of Bethlehem, particularly as it happened in the constellation of Pisces,
a constellation associated with the Jews. Sceptics point out that a far more
spectacular triple conjunction (although in the constellation of Cancer)
happened in 146/145 BC. Similarly, triple conjunctions were seen in Pisces in
861/860 BC and in 981/980 BC, during both of which the separation of Jupiter
and Saturn was less than in 7 BC. Another important point is that the 7 BC
triple conjunction was observed from Babylon, as was the massing of Jupiter,
Saturn and Mars which followed, but the Babylonian records give no sign that
they found the phenomenon of any special interest.
An
occultation
A recent and interesting
suggestion is that the Star of Bethlehem might have been an occultation. At
first sight this seems unpromising. Between 20 BC and 1 AD the Moon passed in
front of (occulted) the four main planets (Venus, Mars, Jupiter and Saturn) 170
times. In other words, it is hardly a rare event. However, when we calculate
which of them would have been visible from Babylon in a dark sky, the number
reduces in to just 5 over the 20 years – somewhat better, although still hardly
a rare event.
Recently, however, Michael
Molnar of Rutgars University has drawn attention to an occultation of Jupiter
by the Moon in 6 BC. This took place in the constellation of Aries and was
similar to a later occultation of Venus which may be referred to in a coin
known as the Antioch coin. This coin shows a Ram (Aries?), the Moon and a
bright star, and what appears to be the track of a planet.
Molnar suggests that the 6
BC occultation was the Star of Bethlehem because of its astrological
associations, Aries being the ruling star sign of Judea and Jupiter symbolising
a king, with the occultation – the reappearance of the planet from behind the
Moon – symbolising a royal birth.
I am sceptical because the
March 17th 6 BC occultation took place very close to the Sun and
just after sunset. It is hard to believe that it would have been observable
with the Sun just 3 degrees below the horizon and Jupiter 5 degrees above it. This
theory though has been very well received by many astronomers and popular
writers and may be more than just an interesting anecdote in the story of the
Star of Bethlehem.
Comet(s)
A theory which has been
popular for many years is that the Star of Bethlehem was a comet. There is no
doubt that a bright comet is a very spectacular event and would be an
impressive "star", but scrutiny of the Chinese and Babylonian
chronicles reveals no evidence of a bright comet. There is an event observed in
5 BC which may be an account of a comet, but there is no description of
classical elements in Chinese reports such as the tail and the comet’s movement
which make it doubtful that this was a comet. Similarly, the Chinese reports
imply that the object was stationary – most uncometary in an object seen for
two and a half months.
Such doubts do not stop
many "stars" from being depicted as comets – this practice is
particularly widespread in Spain where stylised comets which show a large star
with a flowing curved tail (thus getting the best of both worlds), adorn
Christmas trees and buildings everywhere.
The biggest problem though
with the comet theory is that comets have the wrong associations. Throughout
history comets have inspired fear and dread. Such attitudes still exist today
in some parts of the world. Traditionally, comets have been associated with
death, war, famine and disaster; such associations are known to have dated back
at very least to Chinese astronomy several centuries BCE. In “Julius Caesar”
William Shakespere sums up the prevailing attitude to comets:
“When beggars die there are
no comets seen, but the heavens themselves blaze forth the death of princes.”
Lest we think that such
attitudes are primitive, when Comet Delavan appeared in 1914 it was widely
believed by even the educated public to be a harbinger of the forthcoming World
War.
How reasonable is it to
think that an event so intimately linked with death and disaster in so many
cultures, including the Judeo-Roman culture around the time of the Nativity
(the appearance of a bright comet in 77BC, which supposedly had the form of a
sword was, at the time, associated with the fall of Jerusalem), could have been
regarded as a sign of the birth of the Messiah? Had a bright comet appeared,
surely King Herod would have known of it and would have feared it, something
completely different to the impression that Matthew’s Gospel gives.
Nova
If the object seen by the
Chinese in 5 BC was not a comet, then it can only have been a nova (we know,
from the lack of a radio source and a visible remnant that it was not a supernova,
despite its long duration of visibility). The position (southern Aquila) is
consistent with having been a nova, although a little further south of the
plane of the Milky Way than is normal.
The date of its apparition
(March 5 BC), coinciding with the best guess as to the date of the birth of
Jesus, its position in the sky (in the east at dawn) and long duration of
visibility (more than 70 days), make this a very plausible Star of Bethlehem. Again
though, we would have to ask the question "why this nova?" given that
the Magi must surely have observed dozens of novae over the centuries that the
spent watching the sky. It is a little hard to see what would have made this
event particularly significant to the Magi – apart from the fact that its date
coincides, as far as we can guess, with the date of the Nativity.