About 2,000 years ago, St. Matthew recorded that the birth of Jesus was accompanied by something extraordinary that appeared in the sky above Bethlehem. For centuries since, astronomers have pondered the nature of this Star of Bethlehem.

Was it a one-time, supernatural event, never seen before and never seen since?

While that is a possibility, it seems unlikely that St. Matthew would have been the only person to record such an amazing event as that.

Another possibility is that the Star of Bethlehem was a rare but natural celestial event that might have gone unnoticed by the masses but would have caught the attention of sky watchers and astrologers, such as the Magi mentioned in St. Matthew’s gospel.

Assuming this to be the case, what type of celestial object could have appeared as the Star of Bethlehem?

A bright comet can be a spectacular sight in the sky, but a bright comet would have been noticed and recorded by sky watchers world wide, so it seems unlikely that St. Matthew would have been the only person to record it.

The death of a nearby star in a supernova explosion would have created a sudden and brilliant star in the heavens. Historically, bright supernovas have appeared in our sky about every 300 years.

The last one seen in our Milky Way galaxy was Kepler’s Supernova in 1604, so we are overdue for another one. Supernovas leave behind telltale signs astronomers can detect, like expanding clouds of gas.

No such cloud has been discovered that dates back to the time of Jesus’ birth, so the Star of Bethlehem was probably not a supernova. Besides, supernovas don’t move around in the sky, and St. Matthew specifically recorded that this star led the Wise Men to Bethlehem where it came and stood above where the young child lay.

Our best natural explanation for the Star of Bethlehem involves an unusual grouping of the bright planets in the sky. Planets are “wandering stars” that do move around against the background stars. Plus a conjunction of bright planets might have gone unnoticed by the masses, but might have caught the attention of sky watchers as a sign heralding the birth of a king.

Running the solar system clock backwards, astronomers have identified two very unusual groupings of the planets, either of which could have been the Star of Bethlehem.

The first one occurred in 7 BC. During the course of several months that year, the planets Jupiter and Saturn had a very unusual triple conjunction, passing each other three times, while in the constellation of Pisces, the Fish.

Jupiter was considered the king of the planets and the constellation of the fish was associated with Israel, so astrologers, such as the Magi, might have interpreted this a sign of the birth of a king in Israel.

The second unique planetary alignment occurred on the morning of June 17 in the year 2 BC. That’s when the two brightest planets, Jupiter and Venus, appeared to pass so close to each other that they would have briefly blended into a single bright star.

The date of this event doesn’t coincide as well with Jesus’ estimated birth date, but it certainly would have been spectacular.

Could one of these unusual planetary conjunctions have been the heavenly sign that launched the Magi on their journey westward to Jerusalem where they found the infant Jesus?

Unless other ancient records are found that give us more and better clues, this is as good a guess as any that astronomers can make.

This Christmas season, both Venus and Jupiter are visible in our morning sky. Dazzling Venus glows brightly in the southeast right before sunrise, while brilliant Jupiter gleams high in the southern sky.

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Craig Daily Press and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Westlake’s new “2016 Cosmic Calendar” of sky events on his website at jwestlake.com. It features 12 of his best sky photos and a day-by day listing of cool celestial events that you and your family can enjoy watching in 2016.