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Wow. Have you ever seen a conjunction this close?

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A very special conjunction from back around the time of Christ has been noticed and written about by several people over the years. One was Ernest Martin in his book “The Star that Astonished the World”, available online at http://www.askelm.com/star/. The star referred to in the title was a special conjunction of Venus with Jupiter on June 17, 2BC. In searching for the date of Jesus’ birth, he identified this conjunction as well as several other astronomical events in the year 3/2BC, and ended up choosing the triple conjunction of Jupiter with Regulus beginning in September of 3BC as probably marking the date of Jesus’ birth. He didn’t correlate any particular historical event with the June 17 conjunction. Dr. Martin credits Roger Sinnott with being the first to notice and write about the June 17 conjunction, in Sinnott’s article “Thoughts on the Star of Bethlehem”, published  in the December 1968 issue of Sky and Telescope magazine.

More recently Rick Larson of www.bethlehemstar.net looked into these things and was able to piece together more of the picture. The triple conjunction of Jupiter with Regulus in 3BC is a fairly rare conjunction since it starts right at the Hebrew New Year, so he too takes it to be significant. But there’s an interesting correlation between the first conjunction of Jupiter with Regulus and the June 17 conjunction of Jupiter with Venus. The Hebrew New Year corresponding to the first conjunction of Jupiter with Regulus begins at sunset of Sept 11, 3BC. Counting from this date to sunset of June 17, 2BC (count just 28 days for February of this year) the span is 279 days. The June 17 conjunction actually occurs near the beginning of the following day, after sunset of June 17. So we add one more to 279, getting a total of 280 days. 280 days is 40 weeks, the normal period of time between conception and birth of a baby.

So… suppose the conjunction of Jupiter with Regulus at the Hebrew New Year marked Gabriel’s announcement to Mary. This wouldn’t be the first time that Gabriel’s timing had corresponded to a conjunction of Jupiter with Regulus (see This will be a sign to you. Watch for it. Daniel 10-11 for details). And there’s something special about these feast times of Israel, as times that God sets aside for meeting with His people. So it would make sense as the time of Gabriel’s announcement to Mary. And if Gabriel’s announcement and the conception of Jesus occurred at the Hebrew New Year, this provides June 17 with the significance that it seems to deserve. It’s in just the right place to mark Jesus’ birth.

Now, why exactly is the June 17 conjunction so special? Why does it “deserve” some significance? I took a fresh look at this yesterday and need to pass on what I found. It’s not necessarily that it was an especially bright conjunction. Yes, it was bright. It had the combined brightness of Jupiter and Venus, the two brightest planets. But this could be said of any conjunction of Jupiter and Venus.

In chapter one of his book, http://www.askelm.com/star/star001.htm, Dr. Martin reports:

This occurrence [the conjunction of June 17, 2BC] also impressed the astronomers at Griffith Observatory in Los Angeles. In the year 1980 a symposium was held at Griffith attended by various scholars and the staff of the observatory. The meeting was convened to discuss the historical significance of several astronomical events that occurred in the years 3 and 2 B.C.E. It was led by the noted chronologist and biblical historian Professor Jack Finegan of Berkeley, California. At the meeting it was determined that the unique conjunction of Jupiter and Venus and other astronomical events covering an 18 month period from May, 3 B.C.E. to December, 2 B.C.E. were of such historical and astronomical significance that there was need for modern scholars to reappraise the historical accounts associated with these outstanding astronomical occurrences.

This prompted the astronomer John Mosley of Griffith to program the Zeiss instrument in the observatory theater to show the heavens from 3 to 1 B.C. When this was done, there was a private viewing to the observatory staff of this interesting period in astronomical history. The technicians who directed the planetarium instrument back to that period projected the appearance of the sky on the theater dome of the planetarium. When the twilight period of June 17, 2 B.C. came into view, the planets Jupiter and Venus were seen in a magnificent conjunction. All the audience expressed wonderment over this rare sight.

What was being observed was what the astronomers at Griffith had already determined by calculation would happen. The visual effect, however, was stunning. Everyone in the planetarium theater was now seeing it as those in Babylon and Jerusalem would have observed it almost 2000 years ago. What was being witnessed was one of the most spectacular astronomical displays of two planets merging together that the planetarium staff had ever observed. Without doubt, this conjunction of Jupiter and Venus on June 17, 2 B.C.E. would have caused astonishment and awe to people living in the world in 2 B.C.E

So Dr. Martin has first-hand experience of something I haven’t had the privilege of seeing. He’s seen a full-sky reconstruction of this event in a planetarium setting, while the reconstructions I’ve studied are just on the flat display of a computer screen. So my intention isn’t to contradict Dr. Martin’s report. I’d love to see the same thing myself. But up until now I’ve had a mistaken impression about the June 17, 2BC conjunction – that the special thing about it was just its brightness, and I think that came from a misunderstanding of what Dr. Martin is saying here. In another place he says:

…there was the extremely close conjunction of Jupiter and Venus on June 17, 2 B.C.E. This was when the planets appeared as one gigantic “star” in the western sky. It is interesting that this conjunction occurred at the exact time of the full moon. While the western quarter of the sky was being adorned by this brilliant planetary spectacle, the dome of the sky itself was being illuminated from the east by the resplendence of the full moon. In that early evening scene, the whole sky was aglow with celestial brightness.

So the presence of the full moon at the same time as this conjunction contributed much to the overall sense of brightness and awe that Dr. Martin and his companions experienced. As for the Jupiter/Venus conjunction itself, as I look into the details, the striking thing I’m seeing isn’t so much about its brightness as it is the precision and closeness of the conjunction. Its closeness is what sets it apart as probably being quite a rare occurrence (see the section “how rare is rare?” for more discussion of this).

If Jupiter and Venus are as close as about 1/2 of a degree (30 minutes) apart in the sky, they’re close enough to be an interesting event. But that night we find an exceptionally close conjunction of Jupiter and Venus, separated by just 40 seconds (1/90 of a degree) at their closest – close enough that to the ordinary observer they’ll appear to be joined into a single spot of light. From our observation point in Jerusalem, the Stellarium program shows this closest point to occur at 11pm, below the horizon. This seems at first to detract from the potential significance of the conjunction as a sign. If it was a sign meant for the nation of Israel, it should have been visible from Israel, right?

But to nail down the timing of astronomical events to the probable hour and minute, when we go this far back in time a “Delta T” factor is needed to correct for variation in the Earth’s speed of rotation. Stellarium doesn’t yet include any built-in correction for this, so its results have to be manually adjusted. NASA’s estimate of the Delta T value for this date is 10540 seconds, or 2 hours and 55 to 56 minutes. Subtracting this from 11pm, we get about 8:05pm Jerusalem time as the probable time of the closest conjunction. This means that the closest conjunction actually was visible from Jerusalem, close to the middle of the three-hour span during which the conjunction was visible that night, halfway between sunset and the setting of Jupiter and Venus on the horizon.

That night as the Sun set at 6:40pm Jerusalem time (9:35pm before Delta T correction), leaving Jupiter and Venus shining in the Western sky, they were found to be separated by only 2 minutes and 40 seconds, or about 1/20 of a degree. At 6:45pm the full moon rose, adding to the brightness of the night sky. About an hour and a half into the night, at 8:05pm Jerusalem time (11:00pm before Delta T correction), Jupiter and Venus reached their closest conjunction with a separation of only about 40 seconds from center to center (Compare this to the diameters of Jupiter and Venus – 30 seconds and 25 seconds at this point in their journeys across the sky). This was almost as close as they could get without one being partially eclipsed by the other, which would have reduced the brightness. I had read some similar things in Ernest Martin’s book about the closest point of conjunction, but didn’t quite grasp what it was saying until I saw it for myself (see below). Another hour and a half into the night at about 9:40pm Jerusalem time (12:35am before Delta T correction), Venus and Jupiter have begun to move apart, and they set on the Western horizon with a separation of about 3 minutes and 5 seconds. Summary:

  • 6:40pm, sunset – Jupiter and Venus at 2m 40s separation
  • 8:05pm – Jupiter and Venus at closest conjunction of 0m 40s
  • 9:40pm – Jupiter and Venus set at 3m 5s separation

Here’s what the closest point of the conjunction looks like as reconstructed by Stellarium, zoomed in to show how it would have looked through a telescope. It’s magnified enough that we can see the moons of Jupiter, but even at this magnification we still see Jupiter and Venus side by side. Or maybe better to call it end to end – north pole to south pole. If there had been cameras in those days, somebody could have gotten a photo of both these planets all in one shot, and close up enough to show the distinctive colors and features on their surfaces:

JupiterVenus conjunction of June 17, 2BC

Jupiter/Venus conjunction of June 17, 2BC

 

We’ve seen already that Jerusalem was in a prime spot for getting the best view of this conjunction at its fullest, near the middle of the 3-hour window of visibility. The same would be true of the nearby city of Bethlehem. But it wasn’t visible from just anywhere. If we change our observation point from Jerusalem to Rome and again make the needed Delta T corrections, we find the closest conjunction occurring while the sun was still shining, about a half hour before sunset. So from Rome the conjunction wouldn’t have been seen at its closest point.

What about where the wise men came from? It seems likely that they didn’t begin their journey until after this conjunction, probably taking its closeness and precision as the final piece of evidence needed to send them on their way to look for the newly-born King of the Jews. A good guess is that the wise men came from Babylon. When we change our vantage point to Babylon, taking Al-Hillah, Iraq to be its approximate location, we find that the closest conjunction was indeed visible from there, just a half hour later, about 2/3 of the way through the 3-hour window of visibility before Jupiter and Venus set on the horizon.

How rare is rare?

We saw that the 2BC conjunction of Venus with Jupiter showed a separation of just 40 seconds between them at their closest approach. This looks impressive when we see it, and people speculate that it must be a pretty rare occurrence. Let’s take a look and see how rare it really is.

On the average there is a conjunction between Venus and Jupiter about once a year, so it’s not a trivial task to check them all out and verify how often they come as close as this. To make it a more manageable task, for now let’s limit the span of years that we’re interested in. I’m taking the 2BC conjunction to be a sign of Jesus’ birth, along with the triple conjunction of Jupiter with Regulus which marked that particular Sabbath year. I’ve found evidence that at least the conjunction of Jupiter with Regulus is likely to have been given to Daniel as a sign for his people to watch for – probably given as part of a vision on the bank of the Tigris River in 537BC (Daniel 10-11). Was the conjunction of Venus with Jupiter also explicitly given to him as a sign to watch for? Or was its closeness and precision alone enough to communicate something significant to the wise men when they saw it? In order to evaluate the possibilities, it would be helpful to know whether any other similar conjunctions occurred between the time of Daniel and the time of Jesus’ birth. Daniel was probably born around 620BC, so a good period to look at would be 620BC to 33AD.

Another thing that can help in the search is some understanding of the pattern followed by these conjunctions. Just looking at them chronologically year after year, we find what seems to be random variation in the closeness of Venus and Jupiter from one conjunction to the next, with no hint of a pattern. But look ahead by 24 years, and you’ll find the next occurrence to be somewhat similar to the last one, gradually shifting in time of year and position on the ecliptic, and getting steadily closer or farther apart, depending on where in the cycle they’re at. It’s similar to the Saros series of Solar and Lunar eclipses, but with a cycle length of 24 years rather than 18. There are 23 of these Venus/Jupiter series running concurrently, and every 24 years we see one conjunction from each series.

Each of these 23 series has 38 conjunctions, one every 24 years, before it comes to an end and is replaced by another similar series, with the total cycle length being about 910 years. In each 910-year cycle, the closest approach of Venus to Jupiter crosses from positive to negative or back to positive 3 times, giving us three chances of getting one of the exceptionally close conjunctions that I’m interested in. That’s three crossings for each of the 23 concurrent series, or a total of 69 crossings in 910 years, which comes to one crossing every 13 years or so. What I’m calling “exceptionally close” are those conjunctions with a separation of less than a minute, like the one in 2BC. This only happens at one of the crossing points, but it doesn’t happen at every crossing point. In my data so far I’m finding it to occur at about 23% of the crossings, or on the average, once in 57 years.

Here are the actual occurrences of exceptionally close conjunctions found in the 743-year span from 676BC to 68AD. The “+0m 38s” means that at the closest point of this conjunction, Venus is above Jupiter (in the “+” direction) on the ecliptic, and they’re at a separation of zero minutes and 38 seconds. The info in parentheses, (+36 Virgo), shows where on the ecliptic the conjunction occurs. “Virgo” says on which constellation it falls, while +25 identifies the location more precisely, as 25 degrees past Regulus:

  • 618BC 8/5 +0m 38s (+36 Virgo)
  • 571BC 10/17 +0m 38s (+40 Virgo)
  • 554BC 1/28 -0m 3s (+166 Capricornus)
  • 527BC 5/14 +0m 38s (-80 Taurus)
  • 513BC 8/11 -0m 22s (-5 Leo)
  • 469BC 2/26 -0m 37s (+228 Pisces)
  • 464BC 10/29 +0m 12s (+48 Virgo)
  • 149BC 1/28 -0m 43s (+213 Pisces)
  • 148BC 4/20 -0m 22s (-100 Ari-Tau)
  • 108BC 8/5 -0m 52s (+33 Virgo)
  • 2BC 6/17 -0m 40s    (+6 Leo)
  • 42AD 2/25 -0m 37s (+224 Pisces)
  • 49AD 11/16 +0m 49s (+99 Scorpius)

Note: For these closest conjunctions, the location on earth of the observer makes a significant difference in the degree of separation. The measurements shown are from the perspective of an observer in Jerusalem.

So how rare are these exceptionally close conjunctions of Venus with Jupiter? They’re rare enough that when the 2BC conjunction came, it had been 106 years since the last one. The wise men probably had records of previous occurrences that had been observed by others before them, but they were seeing this themselves for the first time in their lives.

Does the existence of 12 other occurrences in this span of time take away from the significance of the one in 2BC? At first look it might seem so. If the others are just random occurrences to which we can’t assign any significance, then it would seem less likely that the significance we’ve assigned to the 2BC conjunction is really valid. But this is turning out to be a very intriguing list. I find that of the 13 occurrences, 5 of them occur in Sabbath years and 4 of them occur in the first year of a Sabbath cycle. Two of these 9 are in the right places to also mark the beginning and end of a Jubilee cycle. These correlations give them a good probability of having true significance in the Creator’s timetable. And as I look at the Sabbath and Jubilee years marked by these conjunctions, they appear to correlate with things like the 70 years of Judah’s captivity and the first 7 sevens of Daniel’s 69 sevens which were to help identify the coming of the Messiah. This could lead to some very fruitful further study and discovery, and to nailing down the meanings of these visions of Daniel with more certainty than ever before.

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