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Article by John Mosley - 1981
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Common Errors in "Star of Bethlehem" Planetarium Shows

John Mosley
Program Supervisor
Griffith Observatory
2800 East Observatory Road
Los Angeles, California 90027

[reprinted from the Planetarian, Third Quarter 1981]

[Note: the audience of this article is planetarium professionals who present annual public shows on the "Star of Bethlehem".]


Since the 1940's most of the planetariums in the western world have presented a show on the Star of Bethlehem in what has become one of the newer Christmas customs. As the first Christmas shows are older than most planetariums (and most planetarians!) we have learned from each other and from those who went first and for the most part we all present shows that are quite similar and that have not changed dramatically in at least a generation. (How did you learn to give your first Christmas show?)

Unfortunately we have copied each others' errors along with everything else, and these errors have been repeated in lectures and in print to where they have become planetarium folklore and myth. Yet despite their time-honored status of respectability, they are still errors, and if we represent ourselves as trusted sources of information we have an obligation to be as accurate as possible, even on minor points.

Each of the following eleven statements often heard in planetarium shows is either factually incorrect or is misleading and requires qualification.

1. Kepler suggested that a triple conjunction of Jupiter and Saturn was the Star of Bethlehem

Although Kepler was the first person to calculate that the triple conjunction had occurred in 7 B.C., he actually suggested something quite different.

In December, 1603, Kepler watched a conjunction of Jupiter and Saturn that took place in Sagittarius in the morning sky. (Note: this was a single conjunction.) The conjunction was astrologically important because it took place in a constellation that was one of the points of the Fiery Trigon, and was to be followed the next autumn by a triangular grouping of Mars, Jupiter, and Saturn -- a fiery triangle in the Fiery Trigon. As an omen this was surpassed only by a comet, and many astrologers in 1603 predicted that a comet would be produced by the planets' close proximity late in 1604.

In Kepler's day the location of a conjunction was as important as the conjunction itself. The 12 signs of the zodiac were divided into four trigons, each made of three associated and equallyspaced constellations. Pisces, Cancer, and Scorpio were the Watery Trigon whil e Sagittarius, Aries, and Leo were the Fiery Trigon. JupiterSaturn conjunctions occur at 20year intervals and 117 degrees apart, and shift westward (clockwise) through the signs of a given trigon, remaining within the signs of one trigon for almost 200 years and then shifting into the adjacent trigon. After nearly 800 years (actually 794.4) they begin a new cycle back at nearly their original position as measured with respect to the vernal equinox. The conjunction that Kepler watched had occurred in essentially the same position 800 years before and 800 years before that; Kepler believed the event had happened only eight times since the creation of the world.

The massing of Mars, Jupiter, and Saturn in 1604 was awaited with anticipation. "Somee watched to correct their ephemerides, some for the sake of pleasure, some because of the rarity of the occasion, some to verify their predictions, and others, indeed, to see if there would be a comet as had been expressly predicted by the astrology of the Arabs," Kepler wrote (Kepler) Opera Omnia vol. II, p. 617, as quoted by BurkeGaffney). Mars came first into conjunction with Saturn, on September 26, and then with Jupiter on October 9. Although Kepler missed this last event because of clouds, others in Europe saw the two planets and noted nothing amiss.

On October 10 a new star, as bright as Jupiter, was spotted essentially between Jupiter and Saturn, which themselves were only 9 degrees apart. Kepler observed it carefully until it faded into the sun's glare the following year, and later wrote a book De Stella Nova in Pede Serpentarti (About the New Star in the Serpent's Foot).

While writing this book, Kepler came across a work by Laurence Suslyga of Poland that argued that Christ was born in 4 B.C. Kepler immediately noticed that this was shortly after a triple conjunction that he calculated had occurred in 7 B.C., and wondered if there was a connection. In 1614 he published his conclusions: the triple conjunction of 7 B.C. was followed by a massing of Mars, Jupiter, and Saturn in 6 B.C., and just as the conjunction and massing of 1603 4 had produced a new star, so the events of 7 6 B.C. had produced a miraculous nova, and that nova was the Star of Bethlehem. The biblical triple conjunction took place in Pisces, but the massing that followed took palce in Aries -- one of the fiery signs -- just as the massing of 1604 had also taken place in a fiery sign.

Kepler believed that the star over Bethlehem was a nova placed there specifically to alert and guide the magi. He wrote, "I do not doubt but that God would have condescended to cater to the credulity of the Chaldeans."

Today the supposed nova of 6 B.C. is often forgotten and it is stated that Kepler identified the triple conjunction with the Star of Bethlehem. This incorrect statement dates to the early 19th century when Bishop Munter of Zealand, Denmark, who apparently did not know of Kepler's work or of the nova of 1604 independently suggested that the triple conjunction alone was the Star. He wrote that since the two planets were only one degree apart, weak eyes would have made them out as a single star-clearly a false impression. In a popular chronological handbook published a few years later, Ludwig Ideler, who did not know of Kepler, incorrectly attributed Munter's hypothesis to Kepler. Munter's book was widely read while Kepler's was not, and the error became entrenched in the literature.

2. When determining the date of the birth of Christ, Dionysious Exiguus forgot that Caesar Augustus had ruled under the name of Octavian for four years, and thus made a four-year error.

Dionysius Exiguus (Dennis the Little) was a Scythian monk and prominent scholar who lived in Rome and who had access to the state and church archives including many records now lost to us. It is true that Julius Caesar's grandnephew Octavian ruled as part of a triumvirate under his own name for four years, and was not proclaimed emperor Caesar Augustus until after he defeated the combined forces of Antony and Cleopatra at the navel battle of Actium in September, 31 B.C., but this was common knowledge. Schoolboys were expected to know the story, and a prominent historian working in Rome would not have made such a simple blunder.

Dionysius carefully selected the year we would call I B.C. for the birth of Christ, and set the date at December 25th as was customary in his time, and commenced the Christian Era with January 1, 1 A.D. (six days later) to agree with the stars of the ordinary Roman year, and was probably not far from the mark.

3. When Christ was born, the old Roman calendar was in use, and years were counted from the founding of Rome (AUC).

Although the Romans had devised a system of counting years consecutively beginning with the founding of Rome, in practice this system was seldom used. It would have been nice if they had because then the problems that occupy so much of historians' time would be that much simpler.

The date of the founding of Rome was not known and various dates were given by different authorities. The most commonly accepted date was April 21 of the third year of the 6th Olympiad (= 753 B.C.) as calculated by the antiquarian Varro (116 27 B.C.). In the Varronian Era, 753 B.C. is set to AUC 1. "AUC" is from "ab urbe condita," or "from the founding of the city."

The most common way of designating the year was by referring to the two consuls who were in office that year. For example, "In the following year, when Quintus Fabius and Lucius Fulvius were consuls ..." The Annales Maximi, compiled in 130 B.C., was one of the earliest lists of consuls and was incorporated into later, longer lists. The other common way was to refer to the year of the king or emperor, as "In the ninth year of Hadrian . . . "

By the time of Dionysius Exiguus, a more modern system was in use, and years were counted consecutively from September 17, 284 A.D., when Diocletian was proclaimed emperor by his troops at Chalcedon. This was the "Era of Martyrs," or "aera martyrum," and the years were "Anno Diocletiani." The system was modern in that the count did not begin again with each new emperor. Each year began on August 29th, the Egyptian New Year's Day Thoth i (for example, Anno Diocletiani 100 ran from August 29, 383 to August 28, 384).

While preparing new Easter tables in 525, Dionysius broke with tradition and began the system now in use. He wrote, "We have been unwilling to connect our cycle with the name of an impious persecutor, but have chosen rather to note the years from the incarnation of our Lord Jesus Christ." Dionysius set A.D. I (from "ab incarnatione Domini") equal to 754 AUC, according to reckoning current in his time. His new Christian calendar was not immediately accepted, arid the Diocletian calendar continued in use until the 8th century.

In short, the Romans knew of a counting system that began with the founding of Rome in AUC 1, but unfortunately did not use this system to any significant extent, and the true situation is much more complex.

4. the word for "star" used in Matthew is the same in the singular and plural forms, like "fish," and so the "star" could have been a single object or a group of objects.

The New Testament Greek work for star is "aster" and the word for stars is "asteres", and the two are clearly distinct. The word "star" occurs four times in Matthew, and each time it is singular.

Less clear is why Matthew, if he did want to refer to a group of objects, either planets or stars, did not use the word "astron," (astpov), which means constellation. For that matter he could have used the words for planet "planes aster" -- our word "planet" comes from the plural form "planetes". He did not, perhaps because he preferred to use the more traditional and familiar "aster" which appears 24 times in the Old Testament, instead of "astron" or "planes aster" which do not appear in the Old Testament at all. Although the word Matthew used means a single star in the literal sense, we cannot exclude the possibility that he was deferring to poetry or drama.

In current planetarium shows at the Griffith Observatory we tentatively identify Matthew's "star" with the planet Jupiter, as Jupiter came into close conjunction with Venus twice and with Regulus three times in a 10month period near the time of the nativity.

In any case, the Greek word for star is not the same in its singular and plural forms.

5. "We saw his star in the east" can be translated to mean either "we saw his star while we were in the east," or "we saw his star (as it rose) in the eastern sky," and is ambiguous.

The Authorized King James version of this passage in Matthew reads "there came wise men from the east to Jerusalem Saying Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him." And later, "they departed, and, lo, the star which they saw in the east …" This has been interpreted to mean either that the star was in the eastern part of the sky or that the wise men were in the eastern part of the world when they saw it, but the actual situation is not so ambiguous. The Greekphrase, "en te anatole" simply means "as it rose" or "at its rising" which of course is always in the eastern sky, and does not refer to the location of the observer. Some authors interpret the phrase to mean that the magi observed the star's predawn heliacal rising with the sun, and although this may be the case it is an assumption not contained in "en te anatole." The error is the fault of mistranslation by the committee of scholars working under the sponsorship of King James of England, and has been corrected in the New English Bible to read "We observed the rising of His star…" and "the star which they had seen at its rising …"

Both translations of the Bible agree that the magi came from the east of Jerusalem, probably from Persia.

6. Joseph and Mary went to Bethlehem to pay their taxes. According to an inscription found on a temple in Turkey, this was probablyl the general Roman tax of 8 B.C.

The "tax" that sent Joseph and Mary to Bethlehem is often cited as the major clue in establishing the earliest date for the birth of Christ, and is generally linked with the universal taxation of 8 B.C. This is incorrect for several reasons.

The error dates to the incorrect translation of Luke's word "apographe" as "tax" in the King James version. The correct word for tax is "apotimesis," while "apographe" is properly translated as registration or enrollment and.does not imply the payment of goods or money. Contrast the King James version: "And it came to pass in those days, that there went out a decree from Caesar Augustus, that all the world should be taxed. (And this taxing was first made when Cyrenius was governor of Syria.)" with the corrected New English version: "In those days a decree was issued by Emperor Augustus for a general registration throughout the Roman world. This was the first registration of its kind; and it took place when Quirinius was governor of Syria."

There was a tax in 8 B.C. (and others in 28 B.C. and 14 A.D.) as is recorded on the walls of the Monumentum Ancryanum at the Temple Augusteum in Ankara, Turkey, but this tax cannot be the registration described by Luke for several reasons. That tax was levied specifically on Roman citizens who lived within the empire and who then normally paid at their place of residence or birth. Joseph and Mary were not citizens and were exempt, and in any case would not have had to travel to the place where their family originated. Nor in a general taxation would Mary have had to accompany her husband. And Herod's semiautonomous kingdom was outside the empire proper until 6 A.D., and any tax levied before then would have been ordered and collected by Herod under his own rules.

The correct identity of Luke's registration has been a longstanding puzzle to historians. Recently Dr. Ernest Martin suggested that it was an oath of allegiance made on the occasion of Augustus' Silver Jubilee in 2 B.C. (see Chapter 5 of the second edition of his book). On February 5 of that year, Augustus was awarded the title "Pater Patriae," Father of the Country, in a year of celebrations that commemorated the 750th anniversary of the legendary founding of Rome as well as Augustus' 25th year of rule. In the autograph account of his own life, the Res Gestae, Augustus wrote: "While I was administering my 1 3th consulship the senate and the equestrrian order and the entire Roman people gave me the title Father of My County." The 5th century historian Orosius told how in that same year Augustus "ordered that a census be taken of each province everywhere and that all men be enrolled ... This is the earliest and most famous public acknowledgement which marked Caesar as the first of all men and the Romans as lords of the world ... in this one name of Caesar all the peoples of the great nations took oath, and at the same time, through the participation in the census, were made a part of one society." Josephus relates that "therefore the whole Jewish nation took an oath to be faithful to Caesar and the interests of the king (Herod) ... " An inscription from Paphlagonia in Asia Minor from 3 B.C. records an oath "taken by the inhabitants of Paphlagonia and the Roman businessmen dwelling among them ... The same oath was sworn also by all the people in the land at the altars of Augustus ..." Note that the common thread here is an oath of allegiance required of all the people, citizen and noncitizen alike, both in the empire and its provinces, for the purpose of establishing fealty. This oath was either ordered by Augustus at the time of his jubilee and completed that year (2 B.C.), or was conducted during the year prior to the jubliee (3 B.C.) and the results presented to him as part of the ceremonies.

If Luke's registration was Augustus' loyalty oath we can understand why both Joseph and Mary went specifically to Bethlehem. We are told that Joseph, being of the house and lineage of David, went to the city of David (Bethlehem), while everyone else went into his own city. As a descendent of David he was obliged to return to Bethlehem along with other claimants to the throne of Israel; under Jewish law the right to kingship could pass to Mary's descendants and so she had to accompany her husband.

Planetarians who like to delve into the historical clues used to date the nativity will find that the oath of allegiance to Augustus on his Silver Jubiliee is a more dramatic story than the one about taxes.

7. The "star" was a triple conjunction of Mars, Jupiter, and Saturn. This conjunction, however, could not be seen because the planets were too close to the sun.

This statement contains two separate errors.

A triple conjunction is, by definition, three consecutive conjunctions between the same two planets (or a planet and a star) and happens when the nearer of the two goes through its retrograde loop in front of the more distant. Three planets cannot be said to be in conj unction unless they have precisely the same longitude (or right ascension), and this never happens. The grouping of Mars, Jupiter, and Saturn is more properly called a massing of the planets. There was a triple conjunction of Jupiter and Saturn in 7 B.C. followed by a massing of Mars, Jupiter, and Saturn in 6 B.C.

The massing was clearly visible. Mars and Saturn were in conjunction on February 20, 6 B.C. when the longitudes of Mars, Jupiter, Saturn, and the sun were 351.2, 358.6, 352.0, and 329.8 degrees respectively as interpolated from Tuckerman's Planetary, Lunar, and Solar Positions. (Mars and Saturn were at equal longitude 12 hours later but had set by then; the numbers given here are for 7:00 p.m., Babylon time.) The sun was 21 degrees west of the westernmost two planets and 29 degrees west of Jupiter. All three planets were still visible above the horizon after the end of evening twilight. Robert Victor of Abrams Planetarium clearly saw the MarsSaturn conjunction of February 20, 1966, even though these planets were much closer to the sun than in 6 B.C. and were observed from a higher latitude than the Near East.

8. A triple conjunction of Jupiter and Saturn occurs on the average once every 120 (or 139) years.

Single conjunctions of Jupiter and Saturn occur regularly once every 20 years, but triple conjunctions are not periodic.

Each year Jupiter advances about 30 degrees along its orbit and Saturn advances 12 as seen from the sun, and Jupiter gains on Saturn by 18 degrees. Every 20 years (actually 19.8592) Jupiter overtakes Saturn and there is a conjunction, but this number is an average because we must take into account the position of the earth and eccentricity of the orbits of the three planets. This conjunction is triple if the earth passes both Jupiter and Saturn within about 40 hours of each other-then Jupiter's motion carries it retrograde back past Saturn a second time and then forward again for a third time. These three conjunctions occur within a seven month period.

A search through the published lists of planet longitude positions shows that Jupiter passes Saturn 180 times during the 3600 year interval from 601 B.C. to 3000 A.D. and that 20 of these passings are triple. This implies an average of 180 years between triple conjunctions, but the actual interval varies from 40 to 377 years and is not periodic. The table below illustrating this is courtesy of Robert Victor of the Abrams Planetarium in East Lansing, Michigan.

Incidentally, surprisingly few of us now alive will see another JupiterSaturn conjunction, and none of us will will see the next triple conjunction. The next single conjunction occurs on May 28, 2000, but the planets will be on the other side of the sun; the next occurs on December 21, 2020 and will be visible in the evening sky. The last triple conjunction happened in 1980 , but the next will not be until 2238.

Jupiter-Saturn Triple Conjunctions (in Longitude)601 B.C. to 3000 A.D.Year of Triple Years UntilConjunction Next Conjunction563 - 562 B.C. 40523 - 522 B.C. 377146 - 145 B.C. 1397 B.C. 338332 - 333 A.D. 79411 - 412 A.D. 41452 A.D. 257709 - 710 A.D. 258967 - 968 A.D. 401007 - 1008 A.D. 2981305 - 1306 A.D. 1201425 A.D. 2571682 - 1683 A.D. 2581940 - 1941 A.D. 401980 - 1981 A.D. 2582238 - 2239 A.D. 412279 A.D. 3762655 - 2656 A.D. 139 2794 - 2795 A.D. 1192913 - 2914 A.D. --

9. During the years around Christ's birth (8-1 B.C.) there were no comets or novae seen.

If we include within the period when Christ might have been born the years 5 and 4 B.C., it is incorrect to state that no comets or novae were seen. William's Comet Catalog of 1871 identifies two -- one in 5 B.C. and a second in 4 B.C. Both are described in detail in Chapter 7 of David Hughes' book The Star of Bethlehem: An Astronomer's Confirmation.

The comet of 5 B.C. (number 52 in Williams's Catalog) was first seen between March 10 and April 27, and was visible for 70 or more days. It was a "hut" comet, also called a "sweeping star" or "broom star," and had a tail or rays. It was seen in Capricornus and there is no mention of motion. It may have been a nova, but the description best fits a comet.

In 4 B.C., a "po," or tailless, comet was noted in April 24 in Aquila. There is no way to know whether it was a comet or nova.

Incidentally, older references state that Halley's Comet was seen in 11 B.C., but modern calculations identify it with one seen for 56 days from August to October of 12 B.C.

10. Christ was born in the spring because that is the only time of the year when shepherds are out in the fields watching their sheep.

At first this might seem a useful clue for limiting the time of year when Christ was born, but it is probably of no real value. Shepherds are in the fields with their sheep during most of the year except the rainy winter months when nighttime temperatures average in the 40s and snow is not uncommon. Even so, there is no guarantee that the shepherds were not out in inclement weather if there was reason for it. And some sheep, the "wilderness flocks," remained out all year long, while sheep used in temple sacrifices were watched over all the time.

In short, the shepherds give us no reliable information about the time of the nativity.

11. Early Christians celebrated Christ's birth on December 25 because this is the date of the Roman Saturnalia and the Christians hoped to go unnoticed while the Roman pagans were occupied with their own rowdy celebrations.

December 25th is an interesting date that has astronomical connections, but it is not the date of the Saturnalia.

The Saturnalia was originally a harvest festival roughly equivalent to our American Thanksgiving. It began with a public sacrifice at the temple of Saturn and was followed by feasting. Although originally a one-day festival celebrated on December 17 and followed by two days of general holiday, it grew to eventually encompass seven days (Augustus limited it to three for the sake of business, but it grew back to five). It was a popular holiday when gifts were exchanged, schools closed, and slaves were given special considerations. At no time, however, did the holiday extend to include the 25th.

December 25th became a major holiday in the Roman world in 275 A.D. when Emperor Aurelian proclaimed the date as "Dies Natali Invictus" or "Dies Natalis Solis Invicti" -- the Birthdy of the Unconquerable Sun -- and with the followers of Mithra dedicated a temple to the sun in Roman's Campus Martius. Christmas originated at a time when the sun cult was particularly strong in Rome, and traces many of its customs to sun worship.

The earliest Christians had no reason to keep a low profile on the 25th because it was not until Aurelian that meaningful celebrations took place on that date When Christmas began to be celebrated in the 4th century Christianity was legal and there was no reason to hide. Avoiding the Saturnalia would have been comparable to a modern religious sect avoiding Thanksgiving. When Christianity finally became the dominant religion in the empire, older pagan holidays and ancient customs were given new meanings. An obvious example is Easter which is celebrated with rabbits and eggs--springtime symbols of fertility. Early church fathers found it impossible to stamp out popular pagan practices and compromised by Christianizing them. Mexico provides interesting examples of how the native Indian festivals acquired a thin veneer of Catholicism. Christmas is celebrated at the time it is to give Christian meaning to previously existing pagan celebrations.

The exact date is important astronomically. December 25th is the date of the winter solstice in the Julian calendar (January 6th is the date of the solstice in the Egyptian calendar, still a day of celebration in many countries). The Julian calendar lost one day in 128 years, and Christmas had slipped to December 22nd by the time of the Council of Nicae in 325 A.D. By 1582 it had slipped to December 12th. When Pope Gregory reformed the calendar he restored the date of the solstice to the time of the Council of Nicae, the first great Christian gathering, rather than to the time of the birth of Christ or to the time of the founding of the Julian calendar. That is why the holiday remains on the 25th-the day of the sun's rebirth as proclaimed by Aurelain-although the solstice now falls on the 22nd.

In our annual Christmas show at the Griffith Observatory we like to explore the astronomical and preChristian origins of many modern Christmas customs.


Selected References (1981)

BurkeGaffney, W. "Kepler and the Star of Bethlehem," Journal of the Royal Astronomical Society of Canada, pp. 417 425, December 1937.

Ciotti, Joseph, "The Magi's Star: Misconceptions and New Suggestions," Griffith Observer 42, pp. 2 14, December 1978.

Federer, C. "Rambling Through December Skies," Sky & Telescope, pp. 394 6, December 1968.
Finegan, Jack, Hand book of Biblical Chronology, Princeton, N.J.: Princeton University Press, 1964.

Hughes, David. The Star of Bethlehem: An Astronomer's Confirmation, New York: Walker and Company? 1979.

Marshall, Roy, "The Star of Bethlehem," The Morehead Planetarium, Chapel Hill, North Carolina, 1949.

Martin, Ernest, The Birth of Christ Recalculated, Second Edition, Pasadena, CA: Foundation for Biblical Research, P. O. Box 928, 1980. [since replaced with The Star that Astonished the WorldASK, PO Box 25000, Portland, OR 97225]

Rodman, Robert, "A Linguistic Note on the Christmas Star," Griffith Observer, 40, pp. 89, December 1976.

Tuckerman, Bryant, Planetary, Lunar, and Solar Positions 601 B. C. 1 A.D., Memoirs of the American Philosophical Society, X62, Philadelphia, Pennsylvania, 1962.

Victor, Robert, "The 'Great Conjunction' of 1980-I," Abrams Planetarium, Michigan State University, East Lansing, Michigan, Autumn 1980.


Reproduced from the Planetarian, Vol. 10 #3, Third Quarter 1981. Copyright 1981 International Planetarium Society. For permission to reproduce please contact Executive Editor, Sharon Shanks.

For further information on the astronomy of the Christmas Star, go to the Star of Bethlehem reference page. It contains links to a small number of web sites that present authorative information on the astronomy and history of the star.

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