Virtual Idea Lab

Was the Star of Bethlehem a real event in the ancient sky? Astronomers ponder the mysterious bright object that led the Magi to Jesus' birthplace.

"Star Of Wonder"

by David H. Levy, published in Parade Magazine, December 23, 2001

In 40 years of watching the sky, I've been struck again and again by its spiritual majesty. As an astronomer, I have a scientific interest in the nature of the Sun and Moon, the planets, comets and stars. At the same time, a darkening sky and a starry night never cease to fill me with wonder, a feeling of awe shared with diverse individuals who have watched the sky over thousands of years - including a group of wise men who, 2000 years ago, saw an unusual "star" that eventually led them to the newly born Jesus Christ. The story is told in Matthew 2:1-10. The role of the star is described in the following verses:

     "Now when Jesus was born in Bethlehem of Judea in the days of Herod the king, behold, 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..." Then Herod, when he had privily called the wise men, inquired of them diligently what time the star appeared. And he sent them to Bethlehem... When they had heard the king, they departed; and lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was. When they saw the star, they rejoiced with exceeding great joy."

What was that star? Can its appearance be explained in terms of modern astronomy? Or was it a miracle that defies scientific explanation? Astronomers today, using sophisticated instruments, such as state-of-the-art planetariums, can reconstruct the appearance of the sky on any given night in history - including that miraculous night two millennia ago - and have proposed various theories to explain the Star of Bethlehem scientifically. Such theories are not meant to diminish the mystery and power of the Star or the Christmas story. As astronomers - not theologians or biblical scholars - we read Matthew's words and then use technology, mathematics and the laws of astrophysics to figure out what in creation might have occurred.

The most plausible theory suggests that the star that appeared over Bethlehem may have been Jupiter, the largest planet in our solar system and the second brightest after Venus. To understand how this could be, you need to know a few things about planetary motion. As the ancients knew well, the planets move through the sky relative to the "fixed" stars (planet comes from the Greek word for "wanderer"). Today we know that planets, like the Earth, orbit the Sun. As seen from Earth, they change their positions from night to night, generally moving eastward through a series of constellations known as the Zodiac.

But the planets don't always move eastward. At times they appear to reverse their course, moving westward for two or three months before turning back and heading eastward again. This is called retrograde motion. It happens because the planets farther from the Sun than we are - from Mars to Pluto - take longer to complete one orbit. Thus, Jupiter moves eastward until a time comes when the faster-orbiting Earth overtakes it; then it suddenly seems to be moving west (in retrograde). The effect is the same as when you're in a car that overtakes a slower car. As you begin to pass it, the other car appears to slow down, and at the moment of passing, it appears to move backward. These planetary "dances" have been going on from the time the solar system was formed 4.5 billion years ago and were occurring when the Magi looked at the stars and saw a wondrous event that has not happened since.

The observations of ancient sky-watchers were as accurate as their technology would allow. But, unlike modern astronomers, they saw in the motions of the stars and planets a connection with life on Earth, often portents of significant human events - a practice that today we call astrology. This way of thinking about the stars may have arisen from a real need in early agricultural societies. For example, the "rising" of the star Sirius just before the Sun heralded the annual Nile floods, and the early evening rising of Capella, the goat star, was a sign of winter storms on the Mediterranean. Magi, according to biblical scholars, were wise men - originally a respected Persian priestly caste - whose practices included observing the motions of the stars and interpreting their meaning, a combination of astronomy and astrology as we define those terms today.

Matthew writes that the wise men asked Herod where they could see the newly born King of the Jews, predicted throughout the Old Testament and heralded, they said, by "his star in the east." Educated sky observers of the time would have paid attention when, on September 14, 3 B.C. (our planetarium programs tell us), Jupiter appeared to pass very close to the star Regulus, "the King's star" (which happens to be in the constellation Leo, representative of the Lion of the tribe of Judah ~ LW). When two planets - or a planet and a bright star - appear to get close together, the event is called a conjunction. The conjunction of Jupiter and Regulus occurred in the eastern sky.

In the ensuing months, Jupiter headed eastward, stopped and reversed direction. On February 17, 2 B.C., the planet passed even closer to Regulus. Continuing its dance, Jupiter passed Regulus a third time on May 8. Thus, over nearly eight months, the Magi saw Jupiter appear to draw a circle, or crown, above the King's star, beginning in the east. Would astrologers have interpreted this as a prediction of a royal birth in Judea?

Jupiter's role continues: Five weeks after its third conjunction with Regulus, Jupiter formed a dramatic alignment with Venus, a celestial event almost unheard of in the history of astronomy. The sequence, which took place on the evening of June 17, 2 B.C., was first brought to light by the American astronomer Roger Sinnott. As the sky darkened over Babylonia, Sinnott tells us, Jupiter and Venus drew closer and closer until, at 8:51 that night, the two planets appeared to virtually kiss each other, fusing into a single brilliant star in the western sky, seemingly pointing the direction to Bethlehem.

This scenario, centering on Jupiter, might explain in modern terms what came to be called the Star of Bethlehem. There are other, entirely different explanations. (It could have been a comet, for example. Or it may have been a "miracle," impossible to explain scientifically.) But if we look up at Jupiter on this silent night, it might help to bring back that amazing event from long ago - thanks to the miracle of modern astronomy.

(For an excellent animated sequence of these astronomical events, visit this website: