Look What Happened on Dec. 24 in 2 B.C.

In this post, the third of a series, we will look at the astronomical evidence surrounding the birth of Our Lord, and show how it relates perfectly to the account given in the second chapter of the Gospel according to St. Matthew. (The first post dealt with a revision to the consensus viewpoint regarding the year of King Herod's death. This revision is crucial, because if we accept the scholarly consensus that Herod must have died in 4 B.C., we miss out on all the astronomical phenomena of 3-2 B.C.) With the date of Herod's death as 1 B.C., it becomes possible for the first time to make sense of the pagan, Roman and Christian chronologies, and thus to arrive at a coherent chronology for the life and death of Jesus.

We begin with the story of the Wise Men, found only in the Gospel of Matthew, ch. 2:

The Visit of the Wise Men

2:1 After Jesus was born in Bethlehem in Judea, in the time of King Herod, wise men from the East came to Jerusalem 2:2 saying, “Where is the one who is born king of the Jews? For we saw his star when it rose and have come to worship him.” 2:3 When King Herod heard this he was alarmed, and all Jerusalem with him. 2:4 After assembling all the chief priests and experts in the law, he asked them where the Christ was to be born. 2:5 “In Bethlehem of Judea,” they said, “for it is written this way by the prophet:

2:6 ‘And you, Bethlehem, in the land of Judah,

are in no way least among the rulers of Judah,

for out of you will come a ruler who will shepherd my people Israel.’”

2:7 Then Herod privately summoned the wise men and determined from them when the star had appeared. 2:8 He sent them to Bethlehem and said, “Go and look carefully for the child. When you find him, inform me so that I can go and worship him as well.” 2:9 After listening to the king they left, and once again the star they saw when it rose led them until it stopped above the place where the child was. 2:10 When they saw the star they shouted joyfully. 2:11 As they came into the house and saw the child with Mary his mother, they bowed down and worshiped him. They opened their treasure boxes and gave him gifts of gold, frankincense, and myrrh. 2:12 After being warned in a dream not to return to Herod, they went back by another route to their own country. . . .

This text, together with the chronology established in this first post and the second one, furnish all the information we need to identify the phenomenon that was the Star of Bethlehem. Who were the "wise men from the East"? And why would they, of all people, come to worship a new-born baby, whom they identified as the "king of the Jews"? Israel had not had any kings for almost six hundred years.

Recall, however, that at the end of the southern kingdom of Judah in 586 B.C., most of the Jewish nobility was taken captive to Babylon. One of those taken captive was the young Daniel, who as a gifted interpreter of dreams went into court service under first Nebuchadnezzar, and then Belshazzar, until Darius conquered Babylon. His continued Jewish piety earned him several enemies at court, but he survived the ordeal of the lions' den, and remained at the court until his death at an old age. In that role he may have learned all the observational skills of the Babylonian (Chaldean) court astronomers. One branch of that science led to the founding of astrology -- the notion that the stars influenced events on earth. Astrology is, however, condemned in the Bible, and as a pious Jew, Daniel would not have seen his role for that purpose.

At the same time, however, there is a long-noted tradition in the Bible of of seeing and interpreting signs in the heavens. It is reasonable to conjecture, since the wise men came to "worship" the newborn king of the Jews and to offer him costly gifts, that they were (a) Jewish court astronomers from Babylonia, in the tradition of Daniel; and (b) skilled in interpreting heavenly signs in the Jewish tradition.

[UPDATE 01/17/2010: For a most fascinating look into just how far advanced the ancients were with regard to astronomical calculations and modeling, take a look at this story with its pictures of an early "eclipse computer".]

Let us, then, take note of what the wise men said they saw -- that brought them from Babylonia, a journey of almost a thousand miles (according to the traditional route of the caravans; it took Ezra four full months to cover the distance [Ezra 7:8-9]):

"For we have seen his star in the East" is the traditional language of the King James Version. The NET Bible, which I quoted above, gives the more accurate rendition: "we saw his star when it rose [in the East]." The Greek word which appears in the text of Matthew is anatole, which refers to the rising of astronomical objects in the east -- due to the earth's diurnal rotation.

This is our first important clue as to the identity of the Star -- that it rose in the East, like most other stars. (The North Star, of course, remains fixed, and the ones in its vicinity do not "rise" in the East either.) Other clues in the text are (a) its duration, for a period of at least five months while the Wise Men traveled and met with Herod, before continuing on to Bethlehem; (b) its need for special skills to interpret its meaning and significance (Herod was taken by surprise, and had to ask when the star had "risen"); (c) its ability to seem to travel in a given direction, first from east to west, toward Jerusalem, and then south, from Jerusalem to Bethlehem; and last but not least (d) its apparent ability to come to a stop over Bethlehem.

These clues severely limit the possible candidates for the Star. It could not have been a bright meteor (duration, change of direction), or a supernova (change of direction, lack of observation by Herod [as well as no record of any supernovae in this period in the well-maintained Chinese observational records]), or a comet (same; plus, a comet was anciently an omen of doom, not of joy), or simply some very bright star (same). That eliminates pretty much all but one type of celestial body from consideration: the planets.

"Planet" comes for the Greek word for "wanderer", and planets indeed do wander in their observed motions through the sky as they rotate around the sun. The ones closer to the sun orbit it very quickly; Mercury takes just eighty-eight days, and Venus about eight months. As a consequence of the small size of their orbits, they are not seen as having any very great elongation from the sun -- they generally rise and set with it, and are consequently seen as either "morning" or "evening" stars, depending on their position relative to the sun.

The outer visible planets -- Mars, Jupiter and Saturn -- take much longer than earth to rotate around the sun, and therein lies the reason for their seemingly odd behavior when observed from the earth: they can appear to move backward in the sky as the earth overtakes them in orbit, exactly as a car which you are passing on the freeway appears to move backward, even though both of you are moving forward. This phenomenon is known as "retrograde motion", and from our standpoint on earth, it applies only to the planets whose orbits are outside ours.

So we ask: what were the planets doing in the skies of 3-2 B.C.? Through the abilities of modern astronomical software, we may answer: quite a lot. In what follows, I am making use of a program called "Starry Night", available for both PCs and Macs, and which allows you to re-create on your desktop the stars and planets as they would have appeared in the sky observed from any point on the earth (or elsewhere, for that matter), at any time in the past or future. Not only that, but it allows you to control the time-lapses, in order to see the celestial motions as observed from the chosen point. And finally, it allows one to make Quick-Time "movies" of that observed motion.

Now, then, using Starry Night, let us travel back in time to the skies over Babylon in the early hours of the morning of August 12, 3 B.C. [UPDATE 12/28/2009: As Rolin points out below, Babylon was no longer settled in the first century B.C. The Parthian court had moved to Seleucia, on the Tigris River about 45 miles due north of the site of ancient Babylon. The distance does not make any difference in the views that follow, and so I have left the description as being from the viewpoint of the skies over Babylon.] Watch the movie below, and you will see what the Babylonian astronomers observed rise in the East, beginning about 4 a.m. To orient what you are seeing, I have included graphical (but faint) depictions of the constellations, and you will make out the claw of Cancer the Crab, and the head and the mane of Leo the Lion, as the sky gradually reddens (and cloud wisps appear -- for aesthetic effect) with the rising of the sun:

If all worked as designed (I find one has to be patient, and allow time for the video to load), you saw rise in the east a very close conjunction of the planet Venus (considered since Sumerian times as the "mother planet") with the planet Jupiter just on the boundary between Cancer and Leo. And with this conjunction -- the two planets are still separately distinguishable -- Jupiter, the largest of all the planets and hence known in ancient times as "the King planet", began a seventeen- month odyssey through the skies, from August of 3 B.C. to December of 2 B.C., which displayed each of the characteristics identified in the passage from Matthew, quoted above.

Because all the planets lie along the ecliptic, with Venus being the second closest to the sun, Jupiter has to have a conjunction with Venus at least once every time it makes a conjunction with the sun during its 4,333-day (11.86 years) orbit, and if the circumstances are right, retrograde motion will produce two more conjunctions. Thus, Jupiter-Venus conjunctions occur either once or three times in any given cycle. However, due to the combination of factors explained in this article, the actual close conjunctions (to within half a degree, or 30 arc minutes) of Jupiter and Venus occur only once every eighteen years, on the average. The conjunction just depicted, on August 12, 3 B.C. was at an angular separation of about 15 arc minutes in the dawn hours, and closed to just 4 arc minutes at the maximum approach -- which, however, occurred in broad daylight (at just around 11 a.m.) over Babylon. Thus it was a much more rare occurrence, on the order of about once every 144 years -- or only once, if at all, in the lifetimes of two successive Chaldean astronomers. So the Babylonian magi would have taken note of this conjunction over others -- they had likely never seen anything as close before.

From its close conjunction with Venus, Jupiter traveled westward to make a conjunction to within a third of a degree with the star Regulus, in Leo, on September 14. This again was a noteworthy conjunction -- the King planet with the King star (Regulus, "little king", from the Latin word rex, "king" -- which was the actual name of the star for the Romans, while the Arabs called it "the Kingly One"), in the kingly constellation of Leo. Because Regulus is at a fixed place along the ecliptic, Jupiter-Regulus conjunctions are also once every 11.86 years when they occur. So the conjunction on September 14, 3 B.C., although somewhat closer than usual (20', or a third of a degree) would not have been special but for the preceding very rare close conjunction between Jupiter and Venus. However, as the next film shows, Jupiter's conjunction with Regulus occurred not just once, but three times between September of 3 B.C. and May of the succeeding year, due to the fact that Jupiter's retrograde motion happened to fall precisely in the portion of the ecliptic where Regulus was to be found:

(After you have gotten this video to play, I suggest you use the slider control to run through it again manually in order to see the three separate occasions on which Jupiter comes into conjunction with Regulus. The dates of the closest approaches were September 14, 3 B.C. (20' of separation), February 17, 2 B.C. (51' of separation), and May 8, 2 B.C. (43' of separation). The Chaldean astronomers would have seen this triple conjunction, which traced out a little oval above Regulus, as the King planet "crowning" the King star, after first having made a conjunction with the Mother planet. This could easily indicate the birth of a new king. The fact that the conjunctions all took place in the constellation of Leo would have signified to them that it was a king of the tribe of Judah that was born, because as Jacob blessed Judah's tribe in Genesis 49:9:

You are a lion’s cub, Judah,

from the prey, my son, you have gone up.

He crouches and lies down like a lion;

like a lioness – who will rouse him?

Judah was the tribe that ruled in Judea, where Bethlehem was located, and the Jews take their own name from this tribe. Thus it is easy to see how Jupiter's triple conjunction with Regulus after a close conjunction with the mother planet could have signified to the magi that there was a new king of the Jews born to the west, in Judea.

Jupiter's own motion in the heavens at this point would have been seen as westward from the vantage of Babylon, except when it reversed course and moved in retrograde. Its double return to a conjunction with Regulus after the first conjunction in September might have also been viewed as a sort of beckoning to them: the star started off westward, toward Judea, but then came back as if to say, "Come and follow me", before heading off once again westward toward Judea.

Given that there is at least a single conjunction between Jupiter and Regulus every 11.86 years, what is the frequency of triple conjunctions? As explained in this article, there is a periodic cycle of such conjunctions between Jupiter and Regulus every 83 years (see Table VI on page 23). When they repeat, however, they usually come in pairs, separated by 11.86 years. The reason is that the elongation of Jupiter's retrograde motion (about eleven degrees) is usually sufficient to take in Regulus on two successive orbits around the sun. As Table VI in the cited article shows, the most recent triple conjunction between Jupiter and Regulus occurred in 1967-68, while the next one will not occur until 2038-39. (It will be followed by a second triple conjunction in 2050-51, and then the cycle will not repeat again until 2121-22 and 2133-34.)

The triple conjunction between Jupiter and Regulus that was the "pair" of that in 3-2 B.C. occurred twelve years earlier, in 15-14 B.C., and the "crown" thus formed was actually more centered on Regulus. However, it was not preceded by any close conjunction between Jupiter and Venus, as occurred in August in 3 B.C.: the closest approach between Jupiter and Venus in 15 B.C. was wider by a third than the diameter of a full moon.

And we still are not done with Jupiter's odyssey. After its third conjunction with Regulus on May 8, 2 B.C., Jupiter proceeded to another conjunction with Venus -- even closer than the one in the previous year! Here is a movie of how that conjunction, which occurred as the sun set in the west on June 17, 2 B.C., would have appeared from Babylon, beginning at about 5:30 PM local time. You will see only a faint indication of the conjunction while it is still daylight, but then the movie depicts very accurately how the two planets, at first barely separable visually, appear literally to fuse into one brilliant star as the sky darkens into night. The movie ends about 10 PM, with the conjoined planets sinking below the local horizon:

Now, that conjunction would really have gotten the attention of the magi! The King planet joins again with the Mother planet, but this time in the constellation Leo, not alongside it; and not far from the King star, Regulus. Moreover, the two planets fuse into one, so that they cannot be separated by the naked eye. Yet Venus does not cover Jupiter, which remains slightly above her. But their light combines -- and since Venus as an evening star has apparent magnitude of -4.3 (the brightest nonlunar object in the night sky), while Jupiter's apparent magnitude is around -1.8, their combined apparent magnitude of greater than -6 would have been far brighter than any other object ever seen in the night sky other than the moon itself (which even in its full phase is about magnitude -12).

The Jupiter-Venus conjunction of June 17 set in the west, as seen from Babylon/Seleucia. If the wise men had taken a few weeks to consult and make their plans, and had set out to follow Jupiter to the west beginning in July, then as we have seen from Ezra's example, they might have arrived in Jerusalem some time after the middle of November. They would have been Herod's guests for at least a couple of weeks, while he tried to mine them for all possible information about this new king they had come to worship. And then they would have set out for Bethlehem. What was Jupiter doing in the sky in early December of 2 B.C.? Just watch (this time our movie is filmed from the horizon in Jerusalem):

You are looking southwest of Jerusalem, tracking Jupiter in the night sky, in the constellation of Virgo, the virgin. Each time the frame of the movie refreshes, one day has elapsed. The movie shows the course followed by Jupiter, marking the date intervals every few days. Notice that Jupiter heads steadily lower, toward the horizon, but then comes to a stop, and eventually reverses course. And note the date when it begins to come to a stop -- December 24! For the entire twelve days from December 25, 2 B.C. to January 6, 1 B.C., Jupiter stood still in the night sky, hovering over a point southwest of Jerusalem, as the earth overtook it in its orbit around the sun.

Bethlehem is just five miles southwest of Jerusalem, on the main road. To the magi, it would indeed appear as though the King planet had guided them there. And they would have arrived during the Jewish festival of Hannukah, during which Jews gave each other gifts.

This is indeed a remarkable odyssey on the part of a planet. Two very rare conjunctions with Venus not quite a year apart, the second even closer than the first, with a triple conjunction of Regulus in between, and then another retrograde motion beginning on December 25 while it is in the southwest sky over Jerusalem, in the constellation of Virgo. What are the odds of such a sequence recurring?

As I noted above, the first conjunction of Jupiter with Venus was an event which might have been seen once in every 144 years. Triple conjunctions of Jupiter with Regulus occur in pairs every 83 years. Because 83 is prime, the periodicity of the two cycles will repeat only once about every 11,952 (=83 x 144) years. And that is without regard to the second closer conjunction with Venus, to within 30 arc seconds, which would have been seen only once in about every 1,080 years. Because 144 is commensurate with 2,160 (= 2 x 1,080 = 15 x 144), we could expect the unique course of planetary events seen in 3-2 B.C. to recur again in about 179,280 (= 15 x 11,952) years.

The Nativity was thus, from the standpoint of the signs in the sky, truly a unique event. We still have not, however, exhausted all the Biblical accounts of it. In a later post I will take up another of the Bible's descriptions of the signs at the time of Jesus' birth, and show how they fit in with what has been discussed in the three posts to date. For the present, let us conclude that there were sufficient signs in the sky to give the wise men ample cause to go and investigate the birth of the King of the Jews.