You might’ve noticed two bright points of light setting along the western horizon just before the sun sets. Over the past couple of months, they seem to have been getting closer and closer together. These are not stars, but planets: Jupiter and Saturn.
On December 21st (the same day as the winter solstice), these two gas giants will be in conjunction. A planetary conjunction means two celestial objects appear to be in close proximity to each other from the perspective of Earth-bound observers. A conjunction happens when planets appear incredibly close to one another in the sky because they line up with Earth in their respective orbits.
According to Joe Rao, instructor at the Hayden Planetarium in New York, when these two planets converge on Dec. 21 they will be the closest they’ve been to one another in the night sky since 1623.
This planetary conjunction is also known by some as the “Christmas Star.” It’s a popular belief that the Christmas Star from the Star of Bethlehem story was actually a planetary conjunction. But was the Christmas Star the very same conjunction of Jupiter and Saturn?
Actually, we can roll back time many thousands of years to see what the sky would look like at certain times. We’ve become very familiar with the movements of the stars as well as the planets and can accurately depict where they would be in the sky at a given time, even two-thousand years ago.
So, back in the time of the Star of Bethlehem story, there was indeed a planetary conjunction going on, but it wasn’t Jupiter and Saturn…it was Venus and Jupiter.
You’ll be able to see this year’s Great Conjunction of Jupiter and Saturn for yourself. All you have to do is look towards the west about 45 minutes after sunset on Dec. 21.
Keep in mind that, although they will appear close together in the sky, they are still separated by hundreds of millions of miles.
Irene W. Pennington Planetarium 