The planets Jupiter and Saturn will come together this month in a spectacular conjunction low in the southwestern sky after sunset just in time for Christmas, recreating that famed “Star of Bethlehem.” These two worlds have been near each other in the evening sky since late summer, drawing ever-closer together from week-to-week in preparation for this month’s big event.
One of the theories put forth by astronomers and historians for what the Christmas Star might have been is a rare double—or even rarer—triple conjunction of the bright naked-eye planets Mars, Jupiter and Saturn. And while the Red Planet is indeed in the evening sky looking south (along with the First-Quarter Moon), it’s not anywhere near enough to the other two for a triple conjunction to occur.
Begin the fun at the start of the month by watching Jupiter and Saturn slowly closing in on each other from night to night. (You will see why the ancients called these worlds “planets” meaning “wanderers”—in contrast to the fixed star patterns around them). As the 21st approaches, it brings with it a challenge to see their merging together as a “double planet.” The problem is that sunset is around 5:00 p.m. at that time (which happens to be earliest sunset and longest night of the year since it’s also the Winter Solstice). And the planetary pair sets around 6:30 p.m. So it will be a race to let the sky get dark enough to see them for a while before they dip into the horizon. It’s worth every effort to see this conjunction—even if you have to drive somewhere to get a clear western horizon free of trees and houses. That’s because Jupiter and Saturn will come to within an astounding 6 minutes of arc of each other—or about one-fifth the apparent diameter of the Moon! (And here it’s important to remember that people always overestimate the size of the Moon in the sky—a dime held at arm’s length more than covers it!) Binoculars will give a fascinating view of the two planets in the same field of view and also help following them until they disappear below the horizon.
Two additional points worth mentioning. If you wear glasses for near-sightedness, take them off for a moment to look at the conjunction. Those with good uncorrected eyesight will see a double planet—but without needed corrective vision the two worlds may merge into one brilliant “star”! The other is that the big uncertainty in pinning down exactly what the Christmas Star really was is uncertainty in the time of Christ’s birth—not only what month it occurred but also even what year. In any case, make this year’s conjunction your personal Star!
Finally, as a prelude to this spectacle, the annual Geminid meteor shower will occur on the evening of December 13th into the morning of the 14th. Considered by many as the “King of Meteor Showers”, it’s capable of producing up to 120 “shooting stars” per hour (or as many as two per minute!) at its peak. As your Scientifics Star and Planet Locator will show, the constellation Gemini itself clears the northeastern horizon early in the evening. And this year, the Moon will be nearly new, insuring dark skies all night long.
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of 10 books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.