The Christmas Star--Or Was It Planets?

As sure as mid-December brings out eggnog and enough bearded men in Ared suits to make you believe in cloning, so it inclines astronomers' thoughts to the Star of Bethlehem--the "Christmas Star" that led the Three Magi to visit Jesus in the manger. There has never been a shortage of ideas: 17th-century astronomer Johannes Kepler put his money on a conjunction of Jupiter and Saturn in 7 B.C. which, he thought, would have caused a star to explode. More recent notions have centered on novas (stars that suddenly grow brighter), such as one in 5 B.C. This holiday season, a British scientist makes the case for a comet, while an astronomer at Case Western Reserve University argues for a planetary conjunction. Both imply that the tinsel should be stashed near the Easter baskets: the comet as well as the conjunction appeared in the springtime.

There's no problem discovering what the night sky looked like on any evening of any year. Reliable astronomical records and tables go back millennia. The difficulty is in deciding which year to look up, for the year of Christ's birth remains problematical. Clearly he was born during the reign of Herod the Great, but historians disagree on whether Herod died in 4 B.C., 1 B.C. or in between. Another clue is Luke's assertion that Jesus was "about thirty" when he began his ministry, and was crucified on a Friday during Passover. Only April 7 of the year 30 or April 3 of 33 meets these criteria. With such ambiguous evidence, the best astronomers can come up with is that Christ was born between 7 B.C. and 1 B.C. "The uncertainty surrounding Jesus' birth year leaves a great deal of freedom in choosing the astronomical effect" to link with the Christmas Star, says astrophysicist Kenneth Brecher of Boston University.

The Bible's description also leaves a lot to the imagination. Here is Matthew: "... Behold, there came wise men from the east to Jerusalem ... And, lo, the star, which they saw in the east, went before them, 'til it came and stood over where the young child was." The other three Gospels don't mention a star. Why did Matthew? Astrology was popular at the time, and including a celestial sign in the Nativity story would have given it cosmic significance and helped attract converts. Or perhaps the other Gospel writers suppressed the star. Astronomer William Bidelman of Case speculates that Luke may have wanted to "disassociate astrology completely from his account of the origin of Christianity."

One "star" that might have appeared first in the east and then stopped above the manger is a comet, says British researcher Colin Humphreys in a recent paper in the Journal of the Royal Astronomical Society. (A comet oriented with its tail straight up might appear to stay still.) Chinese records show that a comet appeared for about 70 days in the spring of 5 B.C. Humphreys's conclusion: Jesus was born in that year, between April 13 and April 27.

A spring birth squares with Luke's Gospel, which mentions shepherds tending their flocks by night, something they do only during the spring lambing season. In fact, there is nothing sacrosanct about Dec.25: the birth of Christ was celebrated in January until the fourth century, when it was moved to Dec. 25 to coincide with the Roman observance of the first day of winter. The problem with the comet theory is that these long-tailed wanderers have, from antiquity, been considered portents of doom, not of joyous news like the Nativity. And they don't stay still for long, for the Earth's rotation makes everything in the sky appear to rise in the east and move west.

Bidelman thinks a conjunction of Venus and Jupiter makes a more plausible Christmas Star. Such a rendezvous occurred on Aug. 12 of 3 B.C. and again on June 17 of the following year. He suspects that the time between sightings matches the Magi's travel time from "the east" to Jerusalem and from there to Bethlehem (map). Venus and Jupiter are the brightest objects in the sky, after the moon, so the conjunction "would have been very conspicuous," Bidelman argues. Moreover, the August event occurred in the constellation Leo, which was associated with Judaism because the lion was the symbol of the tribe of Judah. "Seeing the bright 'star' in the morning sky in Leo may have been sufficient to set the wise men off," says Bidelman. If the Magi were astrologers--all working together in the cities of Ahwaz or Ramadan in Persia, or Basra in Mesopotamia--they would have paid particular attention to a planetary phenomenon, not a stellar one. "When the wise men reached Jerusalem, the same object they saw [from their starting point in the east] would have been before them, in the southwestern sky," says Bidelman. If the Magi arrived in June, during the second conjunction, Jesus might have been born in March, 2 B.C.

Scientists who keep track of Christmas Star theories find Bidelman's paper "very well done," as science historian Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics says. But in the end, trying to match Gospel to astronomy is more an intellectual game than a research enterprise, especially since the star can be seen as "not a physical but a spiritual beacon," says Brecher. There will likely never be a definitive answer to the mystery of the Star of Bethlehem. Nor is one needed for those who still see it shine.