The Bimillenary of Christ's Birth:
The Astronomical Evidence
Dr. William P. Bidelman
Warner and Swasey Observatory
Case Western Reserve University
Cleveland, Ohio 44106
[reprinted from the Planetarian,
September 1991]
Everyone knows that we are approaching the two-thousandth
anniversary of the birth of Christ, but exactly when should it be celebrated?
If we accept the conclusion of the sixth century monk Dionysius Exiguus
that he was born on December 25 of the year 1 B.C., then the bimillenary
would occur on Christmas Day of the year 2000 [if we ignore, for simplicity,
the difference between the Julian and the Gregorian calendar]. However,
it is widely believed that Dionysius' date is some four years too late.
Is this correct? It is the writer's belief that the astronomical evidence,
properly considered, indicates that Dionysius was considerably less in error
than his critics have thought.
There have been several attempts to date the events
in Christ's life by reference to astronomical phenomena. Since he was certainly
born before the death of Herod the Great, much has been made of Josephus'
statement that Herod died shortly after an eclipse of the moon visible from
Jericho. Most chronologists, following the lead of the great Johann Kepler,
have assumed that the relevant eclipse was that of March 13, of the year
4 B.C. Yet it has been known for centuries that there were several other
eclipses, one as late as January 10 of 1 B.C., that could also qualify (Mosley
1987 and Sinnott 1986). Regrettably, it must be concluded that the astronomical
evidence on this point is inconclusive and that we must rely on other indications
for the date of Herod's death. And unfortunately, there is a substantial
difference of opinion on this point (Martin 1978).
A somewhat similar situation exists concerning
the date of the crucifixion. While the correlation between date of the month
and day of the week offers only two prime candidates (April 7 of A D. 30
and April 3 of A.D. 33), the latter has been considered preferable because
of a possible connection with a lunar eclipse supposedly seen from Jerusalem
on that date. But Ruggles (1990) has recently shown that there is actually
no astronomical reason to choose between two dates. And, in any case, there
is some uncertainty as to Christ's age at his death.
Another astronomical approach to the problem has
been to attempt to determine the nature and hopefully the time of appearance
of the "Christmas Star," the sight of which inspired the wise
men's visit to Israel (Hughes 1979). In this connection it is well to refer
to Matthew's exact words concerning this phenomenon. I quote from the 1961
New English Bible: "After his birth astrologers from the east arrived
in Jerusalem, asking, `Where is the child who is born to be king of the
Jews? We observed the rising of his star, and we have come to pay him homage.'"
And again: "They set out at the king's bidding; and the star which
they had seen at its rising went ahead of them until it stopped above the
place where the child lay. At the sight of the star they were overjoyed."
There are at least two important points raised
by this account. First, the "star" apparently had meaning only
for the astrologers; no one else is reported to have seen it. And second,
it is implied that the astrologers had lost sight of the "star"
during their trip from their homeland (Babylon? Persia?) to Jerusalem, but
that they then saw it again on their way to Bethlehem.
The fact that the "star" was not generally
seen gives considerable credence to the idea that what the astrologers observed
was not a conventional star like a nova or a supernova but rather what may
be called a "sign in the heavens" such as a conjunction, or close
approach, of two or more planets. And if indeed, a planetary conjunction
was meant, it appears that the same planets were involved in two conjunctions,
occurring several months apart.
Now the idea that planetary conjunctions are involved
in the "Christmas Star Problem" has ancient roots: Kepler, while
believing that the "star" was a newly-appeared celestial object,
nevertheless thought that its coming was associated with several planetary
conjunctions involving Jupiter, Saturn and Mars (Burke-Gaffney 1937). Some
two hundred years later the idea that planetary conjunctions alone were
involved became popular through the work of Ideler. One of the more noteworthy
suggestions was that of Stockwell (1892) (actually of the writer's own institution!)
that the "star" was a moderately close approach of Venus and Jupiter
on May 8 of the year 6 B.C. Stockwell believed the death of Herod to have
occurred in 4 B.C. and also considered only morning conjunctions. His suggestion
was roundly criticized on several grounds by Swift (1893) who, interestingly
enough, noted that Stockwell's conjunction could not have accounted for
the astrologers' second sighting. The solution to the problem came, in the
writer's view, from the discovery by Sinnott (1968) of two notable conjunctions
of Venus and Jupiter revealed in the extensive planetary tables of Tuckerman
(1962). Both occurred in Leo. The first of these was a close morning conjunction
on August 12 of 3 B.C. which Mosley (1987) has shown to have been only about
4.3 arcminutes in separation, while the second was an extremely close (0.5
arcminutes) evening conjunction on June 17 of 2 B.C. Sinnott and others
have assumed that it was the second conjunction that led to the astrologers'
trip to Jerusalem, but the writer prefers the scenario envisaged by Federer
(1968), the longtime editor of Sky and Telescope magazine, who equated the
ten-months interval between the sightings with the travel time from the
astrologers' homeland to Jerusalem.
If one accepts Federer's interpretation, then the
date of the astrologers' visit to Bethlehem can be precisely stated to have
been June 17 of the year 2 B.C. This can be true, of course, only if a later
date for the death of Herod can be shown to be valid. But even if this is
so, are we now much closer to the date of Christ's birth? Unfortunately
we are given no definite information on the age of the "child"
when the astrologers arrived. It may be inferred, however, from Luke's account
of the parents' visit to Jerusalem to present the child to the Lord, which
could not have occurred until at least 40 days after his birth, that this
visit must have been made before the arrival of the astrologers, since the
Holy Family apparently left for Egypt very soon after that time.
Consequently a reasonably accurate estimate of the time of the birth of Christ would be in March or April of the year 2 B.C., perhaps pure speculation around the time of the Lyrid meteor shower. It is difficult to put the birth much earlier in the year in view of Luke's testimony concerning the shepherds in the fields, which seems to imply that Christ was not born in the winter. It may be suggested, then, that the bimillenary birth date might be, say, April 1 of the year 1999.
Two closing comments: (l) the writer has recently
shown (Observatory 111, 121) that pairs of morning and evening conjunctions
such as those described by Sinnott are actually very common. In fact whenever
a Venus-Jupiter morning conjunction of more than 19· elongation occurs,
it is followed about ten months later by a similar evening one. Unknown
both to Stockwell and to Swift, an evening conjunction occurred on March
9 of 5 B.C. While it would be attractive to those preferring an earlier
death date of Herod to assume that the 6 and 5 B.C. conjunctions were involved
in the astrologers' visit rather than the later ones, this would put the
birth of Christ rather early in the year; also it is unlikely that Herod
would have been at his palace in Jerusalem in early March rather than in
his usual winter quarters in Jericho.
And (2) it appears probable to the writer that
the reason that Luke's narrative of the Christmas story differs so significantly
from Matthew's (in not mentioning the astrologers, the "star,"
or the flight to Egypt) may simply be that Luke was anxious to disassociate
astrology completely from his account of the origin of Christianity, whereas
Matthew was not so sensitive on that point. This question can best be left
to the theologians!
Acknowledgments
I am much indebted to Professor Eldon J. Epp of the Department of Religion
of Case Western Reserve University for introducing me to some of the recent
literature on this subject, and to the University Library for making many
references available through interlibrary loan.
References
Burke-Gaffney, W. 1937, J. Roy. Astr. Soc. Canada, 31, 417.
Federer, C. A. 1968, Sky & Telescope, 36, 396.
Hughes, D. 1979, The Star of Bethlehem, (New York: Pocket Books).
Martin, E. L. 1978, The Birth of Christ Recalculated!, (Pasadena:
Foundation for Biblical Research).
Mosley, J. 1987, The Christmas
Star, (Los Angeles: Griffith Observatory).
Ruggles, C. 1990, Nature, 345, 669.
Sinnott, R. W. 1968, Sky & Telescope, 36, 384.
Sinnott, R. W. 1986, Sky & Telescope, 72, 632.
Stockwell, J. M. 1892, Astr. J., 12, 124.
Swift, J. 1893, Astr. & Astr., 12, 105.
Tuckerman, B. 1962, Planetary, Lunar, and Solar Positions 601 B.C. to
A.D. 1, (Philadelphia: American Philosophical Society).
Dr. William Bidelman is now an Emeritus Professor following some 41 years
of astronomical teaching and research at some of America's finest universities.
He has worked mainly in stellar spectroscopy, and is perhaps best known
as the discoverer of the "phosphorous" and "mercury"
stars. This is his first paper dealing with the solar system.
Reprinted from the Planetarian, Vol 20, #3, September 1991. Copyright
1991 International Planetarium Society. For permission to reproduce please
contact Executive Editor, Sharon Shanks.
