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Robert Tulip
2014-Oct-05, 09:41 AM
The long visible conjunction between Jupiter and Saturn for six months from 27 May to 4 December 7 BC is sometimes argued to be a possible basis for the story of the Star of Bethlehem. Here I present some astronomical background for this story, with calculations using SkyGazer 4.5 astronomy software.

The Jupiter and Saturn orbital periods are 11.86 years for Jupiter and 29.46 years for Saturn, producing a conjunction period of 19.85 years. These planets formed the outer boundary of the visible solar system before the age of telescopes. Every 59 years (~=11.86 x 5 and 29.46 x 2), a third Jupiter-Saturn conjunction occurs in about the same point of the sky, 10 degrees of arc further to the east.

The conjunction in 7 BC was in the constellation of Pisces, about 10 degrees west of the spring equinox point. The spring equinox was conventionally considered the start and end of the year, marking the end of winter and the start of spring.

This conjunction of Jupiter and Saturn in 7 BC was the third in the 59 year series in Pisces. The previous two were in 66 BC and 125 BC, at about 20 and 29 degrees to the west of the equinox point in Pisces, while the earlier conjunction in the series in 184 BC was in the constellation of Aquarius. The next JS conjunction in this series, in March 54 AD, was also in Pisces, just 2 degrees west of the equinox, but was invisible behind the sun, whereas the 7 BC event was visible in the east for six months due to the apparent retrograde motion.

The movement of this conjunction point towards the equinox over the centuries provides a possible contribution to the myths of a transition between cosmic ages. Ancient visual astronomy in Babylon had accurate detailed records of planetary positions going back for a thousand years, as used by Ptolemy for his Almagest. Hipparchus of Rhodes used these old records to calculate the speed of precession of the equinox, apparently using the total lunar eclipse on 21 March 134 BC to measure the position of the star Spica with reference to the equinox point.

By comparison to eclipse data, calculation of the conjunction pattern of Jupiter and Saturn was simple. These celestial bodies with orbital periods of about 12 and 30 years (time periods also used in Christianity) were in an observable pattern moving towards the ‘alpha omega point’ of the sky, the beginning and end of the year at the spring equinox. Putting this JS conjunction position movement together with the observed movement of the equinox point into Pisces (which occurred in 21 AD) provides observable data supporting the story of a shift of ages.

Hornblower
2014-Oct-05, 11:42 AM
Suppose for the sake of argument that we take the traditional story in the Gospel according to Matthew literally. From King Herod's bloody-minded reaction after the Wise Men return to their country without reporting to him, we infer that they first saw whatever it was that they referred to as "His star" two years before arriving in Jerusalem, and that it was still visible and "went before them" on their final trek to Bethlehem. How do you reconcile this with a conjunction of Jupiter and Saturn?

Robert Tulip
2014-Oct-05, 12:39 PM
There is no evidence outside the Bible for the traditional birth story, or for associated events such as the massacre of the innocents, so that material can't really be used to assess a scientific analysis. My point here is to show that the ancients had access to a real astronomical observation of a major celestial alignment moving slowly towards the 'alpha-omega' point of the spring equinox, seen in the shift of the conjunction point of Jupiter and Saturn in Pisces every 59 years.

Commentary I have seen about the Jupiter-Saturn conjunction in 7 BC considers it in isolation, from both the 20 year and 60 year patterns that would have been known to ancient sky watchers. The reason this conjunction and not those of earlier times was important in terms of a hypothetical shift of ages was that it was the one closest to the equinox point, as culmination of an observed pattern.

I am drawing attention to the fact that this event was part of a sequence of conjunctions, and that this sequence helps to provide a physical heavenly reference framework for stories which are otherwise quite hard to explain. This pattern would have been important for Chaldean seers but is harder to notice in modern times when their framework of visual astronomy no longer forms the boundary of knowledge.

Here are sky maps of this sequence.
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George
2014-Oct-05, 07:08 PM
That is interesting. In 6 BC, Mars joins them in January and there are two nice crescent Moon conjunctions, first ~ 1/2 deg. with Saturn (Jan. 23rd), then another close one with Jupiter (Feb. 20th). Mercury reaches half-way to them seen at sunset, but poops out.

I would expect that the key is found in whatever constellation was connected to Israel since this astrological group went directly to Jerusalem to ask where to look next. If Pisces held that connection, then you might be correct. There were no solar or lunar eclipses they would have seen. There were two total lunar eclipses visible from Baghdad in March and September of 5 BC.

Reality Check
2014-Oct-06, 02:17 AM
The long visible conjunction between Jupiter and Saturn for six months from 27 May to 4 December 7 BC is sometimes argued to be a possible basis for the story of the Star of Bethlehem.
I would say that the main issue is the assumption that no one noticed Jupiter and Saturn coming together to form the Star of Bethlehem or the star splitting into Jupiter and Saturn. Alternately that the magi (who were probably astrologers) were ignorant about conjunctions. Wikipedia (http://en.wikipedia.org/wiki/Star_of_Bethlehem#Astronomical_object) says that this was not a visually impressive conjunction and did not impress Babylon astrologers.

The Christian ‘alpha omega point’/"story of ages" aspect is evidence that this is a made up story.

Robert Tulip
2014-Oct-06, 12:23 PM
I would say that the main issue is the assumption that no one noticed Jupiter and Saturn coming together to form the Star of Bethlehem or the star splitting into Jupiter and Saturn. Alternately that the magi (who were probably astrologers) were ignorant about conjunctions. Wikipedia (http://en.wikipedia.org/wiki/Star_of_Bethlehem#Astronomical_object) says that this was not a visually impressive conjunction and did not impress Babylon astrologers.

The Christian ‘alpha omega point’/"story of ages" aspect is evidence that this is a made up story.

Ancient astronomers were well aware of the apparent movement of Jupiter and Saturn. My point here is not about this conjunction literally being imagined as the Star of Bethlehem, but rather that this observation series with period 59 years adds to the weight of this as contributing to the construction of the allegorical myth. I agree this should be considered as a made up story, not as a miraculous violation of the laws of nature.

At Matthew 2:2 the Magi say "we have seen his star in the east" and explain they have followed the star to the west. The Jupiter Saturn conjunction rose in the east at about 1 am when these planets came together in May of 7 BC. Due to the retrograde motion of this particular conjunction, they stayed close together for six months, rising four minutes earlier each night with the fixed stars, so at any given time in the evening they appeared to be moving to the west from night to night. By November they were setting together in the west at 1am, and by their separation in December they were setting at 10pm. These times apply around the whole world.

I am drawing attention to this 59 year cycle of JS conjunctions in the same area of the sky because the movement of the conjunction point through Pisces has a good match to various aspects of the star of Bethlehem story, and it is a way to think about how ancient astronomers may have used visual astronomy more extensively than is generally appreciated.

Reality Check
2014-Oct-06, 08:53 PM
I agree this should be considered as a made up story, not as a miraculous violation of the laws of nature.

I would say that the evidence is that this remains a made up story. There is a remote possibility that the originators of the story based it on their memories of this conjunction (conveniently forgetting about Jupiter and Saturn!).
I will draw attention to the little fact that Matthew 2:2 makes the Magi into ignorant people - as you note ancient astronomers were well aware of the apparent movement of Jupiter and Saturn. Even ordinary people would be well aware of the apparent movement of Jupiter and Saturn given the relatively rural nature of life then. No one should think that 2 planets appearing together is an actual star. Otherwise we would see a 59 year cycle of JS conjunctions that are reported as stars.

What you seem unaware of is that Jupiter and Saturn rose together separately, i.e. with an almost 1 degree separation. http://en.wikipedia.org/wiki/Star_of_Bethlehem#Astronomical_object

Modern calculations show that there was a gap of nearly a degree between the planets, so these conjunctions were not visually impressive.[48] An ancient almanac has been found in Babylon which covers the events of this period, but does not indicate that the conjunctions were of any special interest.[48]

Robert Tulip
2014-Oct-07, 06:20 AM
I would say that the evidence is that this remains a made up story.

Yes agreed, rather like some other aspects of the birth narratives which either conflict with known history or science. Stars do not routinely hover over mangers. Trying to explain the story against astronomical data can open up a few lines of enquiry, including this Jupiter-Saturn conjunction. How the scientific observation may have morphed into the gospel story seems to be a question for cultural history more than astronomy.
There is a remote possibility that the originators of the story based it on their memories of this conjunction (conveniently forgetting about Jupiter and Saturn!).Yes, and the range of possible methods includes everything from Chinese Whispers through to deliberate use of allegory.

I will draw attention to the little fact that Matthew 2:2 makes the Magi into ignorant people - as you note ancient astronomers were well aware of the apparent movement of Jupiter and Saturn. Even ordinary people would be well aware of the apparent movement of Jupiter and Saturn given the relatively rural nature of life then. No one should think that 2 planets appearing together is an actual star. Otherwise we would see a 59 year cycle of JS conjunctions that are reported as stars.And given the poetic nature of religious language, it is also possible that major periodic planetary conjunctions could come to be referred to as a star, especially considering the strange behaviour reported of the Star of Bethlehem.The 59 year cycle is of the conjunction in Pisces. Jupiter and Saturn are conjunct every 20 years, at right ascension positions about 123 degrees of arc apart, so each third conjunction is 10 degrees east of the one 59 years before.


What you seem unaware of is that Jupiter and Saturn rose together separately, i.e. with an almost 1 degree separation. http://en.wikipedia.org/wiki/Star_of_Bethlehem#Astronomical_objectThe point is that an unusual star allegedly rose in the east and moved to the west. This is in my view best explained as an allegorical story embroidered from an actual astronomical observation that contains relevant symbolic content. The angular separation of Jupiter and Saturn could be a small factor in this context.

George
2014-Oct-07, 02:51 PM
There simply isn't enough information for us to determine what the true story is. We don't have the original text to work with so was it the star that was in the east or was it that the Maji saw it from the east. It is likely that they were Persians from the Baghdad region located > 500 miles almost due east of Jerusalem, but we don't know for sure who they were or even how many traveled. [We are told that there were three gifts, so, once again, we assume that there were three travelers, which many make Kings.]

The SJ conjunction certainly has merit and it is no surprise that interpreters would refer to the object as a star since "planet" means wandering star. It is highly unlikely that anyone of their day would have a real clue as to what those bright points really were. Two "stars" can become one for simplicity and it is more likely that the guiding star after the Jerusalem visit would have to be something both singular and other than anything astronomical, else there would be no way for starlight to direct anyone to any specific location. I would assume only a supernatural event is presented for the second leg of their voyage, though, as usual, no objective evidence exists to verify such an event. [The lack of an account of baby murders of a very small town is hardly an issue since it would likely have been suppressed and there are worse atrocities today that we never hear about.]

Reality Check
2014-Oct-07, 10:13 PM
... The point is that an unusual star allegedly rose in the east and moved to the west. ....
The point I am making is that no one then would have confused the Jupiter and Saturn conjunction with an actual star, Robert Tulip. Certainly not Magi ("wise men" or astrologers). Probably not even ordinary people who would have seen Jupiter and Saturn get closer together and not form an actual star. This is the opposite of the "ancient wisdom" fallacy.
The evidence is that there is only one story about a star despite these many "major periodic planetary conjunctions". If people were prone to describing conjunctions as stars then there would be many such descriptions.

So the evidence points the other way around - an allegorical story was made up based on other similar myths (see Exodus 13:21 - why should that "pillar" not be a comet :D ). People have been trying to match that star story up with astronomical observations and have failed.

ETA: George, as you can see the SJ conjunction only has merit if we assume that people then were incapable of observing that this was a conjunction. However they were quite capable of distinguishing between stars and planets. So the obvious question is why is it not the Planet of Bethlehem :D.

NEOWatcher
2014-Oct-08, 12:55 PM
The evidence is that there is only one story about a star despite these many "major periodic planetary conjunctions". If people were prone to describing conjunctions as stars then there would be many such descriptions.
While I agree that there is no evidence at this point what it really was, I don't think that the part I quoted applies.

Why not? I'm sure that there were plenty of regular people mostly concerned with the sun and the moon and nothing else.
There were probably other more significant people that didn't watch the sky or bother with the explanation of it other than hearing the astrologer's/astronomer's predictions.

And; why would anyone who does document the planets and conjunctions say "it looks like a star"?

George
2014-Oct-08, 01:50 PM
The point I am making is that no one then would have confused the Jupiter and Saturn conjunction with an actual star, Robert Tulip. Certainly not Magi ("wise men" or astrologers). Probably not even ordinary people who would have seen Jupiter and Saturn get closer together and not form an actual star. This is the opposite of the "ancient wisdom" fallacy.
The evidence is that there is only one story about a star despite these many "major periodic planetary conjunctions". If people were prone to describing conjunctions as stars then there would be many such descriptions. It is logical to assume, as you state, a singular object since there is no mention of "stars" but that does not automatically eliminate the conjunction possibility because the light of greatest importance to the narrative is the one that guided them to a specific house, and we have no idea who wrote the original text. It is likely that the story comes from religious parties who are focused on giving a new-born king account, so a double star (planets) event in a key constellation associated with Judah followed by a singular (supernatural?) light could become simplified into a star (singular) account. Simplicity can infect religious texts, which is why we hear these maji called the "three kings" when there is no mention that they were kings and no mention as to how many there were.

Hornblower
2014-Oct-08, 02:59 PM
As I think I understand it, Matthew was belatedly writing a narrative based on word of mouth handed down over many decades about a virtually undocumented event. He could have used "his star" figuratively in referring to what could have been nothing more than text from a horoscope cast from celestial happenings which the Magi saw as omens about a coming event somewhere near Jerusalem. Without more information about who they were and what sort of details their astrological tenets had, it is hard to be more specific. I think it is most unwise to take the story literally for astronomical purposes.

George
2014-Oct-08, 03:28 PM
As I think I understand it, Matthew was belatedly writing a narrative based on word of mouth handed down over many decades about a virtually undocumented event. He could have used "his star" figuratively in referring to what could have been nothing more than text from a horoscope cast from celestial happenings which the Magi saw as omens about a coming event somewhere near Jerusalem. Without more information about who they were and what sort of details their astrological tenets had, it is hard to be more specific. I think it is most unwise to take the story literally for astronomical purposes. Right, "what could possibly go wrong?" in accuracy applies. The claim they went to Jerusalem for instructions stands out the most to me because it would fit an astrological prediction of a king in this country, whereby they would go to the leaders for further directions. Yet time and even poetic value (e.g. "We Three Kings") has changed today's view of the original account, which no longer exists.

My favorite alteration is the one that the maji were firemen because they came from " a-fire (far)", when said with a Texas draw. :)