Matthew 2:2 adds a detail that has baffled and intrigued Bible scholars and astronomers for 2,000 years: "We have seen his star in the east, and have come to worship him." What was "his star in the east"?
Over the years there have been four main theories:
Halley's Comet: Unfortunately, the nearest appearance was in 11 B.C., which is simply too early for the birth of Christ.
Supernova: This is an exploding star that suddenly fills the sky with light in a brilliant, blinding flash of light. These are unpredictable and very rare, and there is no record in any astronomical records of a supernova in the years surrounding the birth of Christ.
Conjunction of Planets: This is probably the most popular theory. One version suggests that in 7 B.C. Jupiter, Mars, and Saturn came together in a very rare conjunction that only occurs once every 125 years. Another possibility is a conjunction of Jupiter and Venus in 2 B.C. (This last possibility is the one suggested by the "Star of Wonder" presentation at the Adler Planetarium in Chicago.) The conjunction theory has this to favor it: It would explain why the Magi saw it and the people of Israel didn't. Conjunctions don't attract the attention of people who don't normally watch the skies. They aren't highly-visible phenomena like comets or supernovas or meteor showers. But to anyone who watched the stars regularly, a "triangular" conjunction like the one in 7 B.C. would certainly attract extraordinary attention.
A Supernatural Light: This theory suggests that the "star" was not a natural phenomena at all, but rather was a light placed by God in the atmosphere especially for the Magi to see. Those who hold this view (which I myself lean to) point to the shekinah glory of God in the Old Testament. At certain points in history God revealed himself as a bright light in order to guide his people. In this context, we might think of the pillar of fire with which God led Israel in the wilderness.
Excerpted from "We Three Kings" from Keep Believing Ministries (used by permission).