The Christmas Sky

If the seemingly incessant autumnal – and now winter – storms abate for Christmas (and the weather forecast for Spain suggests that they might) you may get a chance to look up at the Christmas sky. If you do so as darkness falls, you will not be able to miss the brilliant, white “star”, low in the west. As the sky map above shows, that “star” is, in fact, the planet Venus. It is low in the sky, even at the latitude of Southern Europe, because it is well south of the celestial equator.

Christmas2019This is the view that you will get from Madrid at 7pm on Christmas Eve, about an hour after sunset. Other cities at similar latitude, such as New York, will give a similar view at the same time relative to local sunset.

Christmas2019_LondonGo further north, for example, to London and look an hour after sunset (5pm local time) and you will see a couple of obvious differences. One is that it will not be fully dark: twilight lasts longer further north. The other is that Venus is significantly lower in the sky because it is so far south of the celestial equator. Go to the beautiful city of Tromsö in northern Norway and you will find that, there, Venus never rises above the horizon at any time on Christmas Eve.

Venus_gibbousLook at Venus with a telescope and you will see that it is a small, featureless disk, showing almost full phase. Technically it is an 83% illuminated, waning gibbous. Venus is by far the brightest object in the sky until the thin crescent Moon passes close to Venus on the nights of December 28th and 29th.

Every year when Venus is visible close to Christmas, which turns out to be 8 or 9 years out of 10, people ask if it is, or was, the Star of Bethlehem.

This is a theory that was widely debated certainly as far back as the nineteenth century. Of course, no one can prove that Venus was not the Star of Bethlehem, in the same way that no one can prove or disprove any of the other, many theories. However, Venus is one of the less likely ones as it was a familiar sight to almost everyone from ancient times and the Magi would most certainly have been experienced sky-watchers.

The root of the word Magi is Μαγος (Magos), in Greek. This is the word used to describe the Magi, or Wise Men, in the original Greek text held by the Vatican that is used as the basis for all translations. Magos is the root of the word, magician, and can be translated also as “astrologer”. Although the Romans banned magic, there are numerous references to who and what Magi were in contemporary Roman histories. Suetonius (70-130 AD) wrote about Nero in the book “Twelve Caesars” that details the lives of the emperors, saying that, tortured by his conscience after causing the death of his mother, Nero:

Quin et facto per Magos sacro evocare Manes et exorare temptavit[i].


He even had rites performed by the Magi, in the effort to summon her shade and entreat it for forgiveness.

Even bearing in mind that the politically correct Suetonius could well have been trying to besmirch the name of the, less than fondly remembered, Nero, this passage gives an idea of who Magi were. Magi were priests associated with Zoroastrianism, a religion still found in some areas of northern Iran and then, widespread in Persia and Armenia. Although Armenia was not incorporated into the Roman Empire until 114 AD, when Trajan made it a full Roman province, a status that, like southern Scotland, it held only briefly, it remained a protectorate of Rome. Later, Armenia was connected to Syria with one of the few Roman roads to head east from the region. For a century and a half, the country had been a strategic asset, contested by Rome and the Parthian Empire before finally falling finally and definitively into the Roman sphere of influence. At the time of the Nativity, Armenia was heavily under Roman influence as its rulers sought protection from the Parthians. Given the close links between Rome and Armenia and the close links between Zoroastrianism and Judaism, it would not be surprising for Magi to take an interest in a Jewish Messiah, given that their religion predicted the coming of a Messiah too.

Later, in 66AD, some fifteen to twenty years before Matthew and Luke wrote their respective versions of the Nativity story, King Tiridates would make a famous visit to Rome to pay homage to Nero. The visit of King Tiridates was much commented by Roman historians and proceeded with a degree of spectacle that differs massively in scale with the very discrete visit of the Magi to King Herod that was described by Matthew. Such was the size and impact of Tiridates’ visit, accompanied by a thousands of members of the court and guards and by Magi, that some experts think that Matthew was so impressed that he added the visit of the Magi to his Nativity story so that Jesus would seem no less important than Nero. The argument is that when, many years later, Matthew, now an old man, wrote his version of the Nativity, he remembered the great impact that the Magi had made in Rome and decided that his story would be all the better and more convincing to the people who he wished to convert if he added this embellishment. It is a tempting, but very unsatisfying theory. It is hard to believe that Matthew simply invented large parts of the Nativity story that he described we such detail: he may have exaggerated some details, deliberately or accidentally, but that is not to invent them completely.

A frequent question that I receive is about what the sky looked like at the time of the Nativity. This is both an easy and a difficult question to answer. Some things can be stated with certainty: we know that the sky looked different at the time of the Nativity.

We know that the Nativity happened about two thousand years ago and a lot of evidence places it no earlier than 8BC and no later than 5BC. For our first look at how the sky was different, two or three years make no difference.

The big change at the time of the Nativity is that Polaris was not the Pole Star. The position of the north pole of the sky – and the star that would be exactly above the North Pole – describes a circle in the sky thirty-two degrees across, with a period of 26000 years. This means that the Pole Star today is not the same as it was at the time of the Nativity, or when the pyramids were built.

In the year 12000BC, the brightest star close to the pole was the brilliant blue-white star, Vega: the fifth brightest star in the sky. Vega will be the Pole Star again in 14000AD. Around the year 7500AD, the Pole Star will be Alderamin, or Alpha Cepheii, a star just a little fainter than Polaris. In 3000BC the Pole Star was the rather fainter Thuban, or Alpha Draconis. At the time of the Nativity there was no bright star really close to the Pole: it fell in a rather barren area of sky between Polaris and the tail of Draco. The nearest bright star was Kocab, in Ursa Minor, but it was about eight degrees from the pole itself. In fact, Kocab, the pole and the much fainter star, Kappa Draconis, formed an equilateral triangle. How much is eight degrees? It is half as much again as between the Pointer Stars of the Plough.

Precession_NA consequence of the pole being in a different place was that, at the time of the Nativity, the ancient skywatchers could see much further to the south in one direction in the sky and much less to the south in the opposite direction. In 2019, the constellation of Crux just straddles the horizon as seen from Jerusalem. In contrast, at the time of the Nativity, the whole of the constellation of Crux would have been visible, well above the horizon, as well as Alpha and Beta Centaurii. In contrast, the other side of the sky, the constellation of Phoenix of which, today, all the brightest stars are visible from Jerusalem, would have been below the horizon.

That was the easy part. What about details? For that, we need the date of the Nativity.

Dionysius Exiguus followed church dogma by stating that Jesus died on March 25th, at the age of 33 years and 3 months, hence the Nativity took place on December 25th. He also stated that his book was published 525 years after the Nativity thus, although he did not state it formally, he implies that the date of the Nativity was December 25th 1AD. This was five years after King Herod died. We have an evident contradiction.

Why the discrepancy? It is known, totally unjustly, as “Dionysius’s Five Year Error”. Where does it come from?

There were two dating traditions for the Nativity. Eusebius of Caesarea (c. 263 – 339), wrote that Jesus was born in the 28th year of reign of Augustus, while the Alexandrian church used the 23rd year of Augustus’s reign: a difference of five years. It appears, that the two churches, which had different ways of calculating the date of Easter, also dated Augustus’s reign in different ways. Formally, Augustus became Emperor in 27BC, when the Senate voted formally to give him power. However, he was de facto emperor from the Battle of Actium (under his given name of Octavian) and the highest power in Rome from his election as Consul in 33BC.

The Senate vote to make Augustus emperor was on January 14th 27BC. Prior to that, he was elected Consul on January 1st 33BC and won the Battle of Actium on September 2nd 31BC. You do not have to be a mathematical genius to realise that more than four years separate the naval action at Actium from the Senate declaration. Similarly, “in the 23rd year” can mean any moment within a twelve-month span. The contradiction in dates is resolved if Eusebius dated Augustus’s reign from Actium and the Alexandrians, from the formal Senate declaration, placing the Nativity in 4 or 5BC: around, or before, the time of the death of Herod.

When in the year the Nativity happened is another question. All sorts of contextual clues have been used in an attempt to define it. One of the most habitual is to suggest that the presence of shepherds keeping watch by night suggests that the Nativity came at lambing time. However, most authors who have repeated this come from temperate countries in which lambing time occurs in Spring. This is not and was not the case in Judea at the time of the Nativity. For five thousand years, the people of the region have farmed Awassi sheep, adapted to the Mediterranean climate.

Shepherds_winter_caveJudea’s climate has distinct wet and dry seasons. The first rains fall in October and the rains end in April. The sheep mate in July and August and start to fatten with the fresh grass in Autumn, lambing in December and January, when the climate is at its wettest and fodder is plentiful. However, whilst not harsh, the climate is cool and humid and, as they have done for thousands of years, at night, the shepherds lead their flocks down into the plentiful limestone caves to pass the night. The Church of the Nativity is built over one of these caves and, local legend is that the silver Christmas Star in the Chapel of the Nativity, down in the cave, marks the spot where the manger, in which baby Jesus lay, was set in the cave.

Shepherds would sleep out with their flocks between March and September to guard against predators, as even foxes are a danger to new born lambs and, in Roman times, the fauna of the Mediterranean was very different to now. Then, foxes and wolves would have been the least of the shepherd’s problems as elephants and bears roamed the whole of North Africa, while the Atlas Lion ranged from Morocco in the west to Pakistan in the east. Quite apart from wolves, a shepherd in Bethlehem might have needed to scare off a mother bear with her cubs, or a hungry lion looking for a free meal.

The fact that the inn was full suggests that the Nativity occurred at a time of great transit. A plausible candidate is the time of Passover (April 1st in 6 BC, March 21st in 5 BC, April 10th in 4 BC): a time when families would travel considerable distances to return home for the celebration.

The evidence that we have suggests that King Herod probably died before the Passover of 4BC so, let us assume that the Nativity was in the second half of March 5BC. We also know that about this time (the month that started on March 10th 5BC), both Chinese and Korean astronomers saw a bright object in the eastern sky between northern Capricorn and southern Aquila. There is a lot of debate as to just what they saw, but the stationary position over two and a half months and its proximity to the Milky Way suggests that it was more likely to be a nova than a comet. In addition, we know that, by late May 5BC, when the Chinese lost sight of the object, China was deep into monsoon season when any kind of astronomical observation was likely to be impossible: in other words, most likely the object was still visible, but hidden to their eyes by constant clouds and rain.

So, let us let fly our imaginations and suppose that we were looking east from Persia close to dawn on March 1st 5BC and that Nova Bethlehem was visible and at peak brightness. What would we have seen? It might have looked something like this, with the waning crescent Moon low in the south, in the constellation of Sagittarius and Nova Bethlehem in the south-east.


Probably, we will never know, but it is, at very least, possible that this was the sky that drew the Magi to Bethlehem.




[i] Suetonius, Vita Neronis, 34:4

3 thoughts on “The Christmas Sky

  1. First let me thank you for your 2019 posts. I have enjoyed reading them.
    I am one of those that consider it plausible that the Star of Bethlehem story was influenced by the visit of Magi to Nero in AD66 as there are uncanny similarities with the story in Matthew’s gospel: They bowed down. They offered gifts. They recognised him as a god. On leaving they returned home by a different route. Included perhaps by the author(s) of Matthew’s gospel to imply that Jesus was at least as important as Nero and therefore should be recognised as a god.
    Happy 2020.


    1. Hello Rod

      Nice to hear from you. Happy New Year! I suppose that it all rests on just how much time passed between the time that Tiridates visited and the time that Matthew’s Gospel was set down. Possibly we will never know. And it is possible that the Star really did appear at the Nativity and the magi not… or vice-versa. Of course, in the Apocryphal Gospels there is an account that appears to be a pretty faithful description of the visit of Tiridates, transposed in time and place to the Nativity.


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