December Sky Event: Jupiter, Saturn Will Align To Create Rare 'Christmas Star'

Skywatchers will be in for a treat later this month as Jupiter and Saturn are preparing for quite a show. On the same day as the winter solstice, the two giant planets will align to form a "Christmas star" that has not been seen in about 800 years.

Jupiter-Saturn 'Great Conjunction'

Looking up at the sky this year, skywatchers may have noticed two particularly bright objects that have been traveling together across the sky. These are actually Jupiter and Saturn and they have been moving closer to each other.

On Dec. 21, the same day as the winter solstice in the Northern Hemisphere, the two planets will align in the sky and appear so close together that they will be just a tenth of a degree apart. According to NASA, that's about "the thickness of a dime held at arm's length."

Such an event, wherein the two objects align with the Earth and appear so close together in the sky, is called a conjunction. It typically happens once every 19 or 20 years. But this year's event is the "great conjunction" between Jupiter and Saturn since they will appear exceptionally close together.

"In fact, Saturn will appear as close to Jupiter as some of Jupiter's moons," NASA said, calling the Dec. 21 event the "greatest great conjunction" in 60 years, since Jupiter and Saturn will not appear this close again in the sky until 2080.

800-Year Alignment

As Forbes explained, the planets won't really be close together. Instead, they will simply appear as such because of the rare alignment. The event on Dec. 21 will be quite exceptional because it's something that hasn't been seen in about 800 years.

"Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to be to one another," Partick Hartigan, Rice University astronomer, said as per Forbes. "You'd have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky."

Christmas Star

It is believed by some that what's known as the "Christmas star" or the "star of Bethlehem" was actually triple conjunction between Jupiter, Saturn and Venus, Forbes explained. This year, skywatchers may catch a glimpse of the Christmas star with Jupiter and Saturn's great conjunction and, on the same day, as the shortest day of the year in the north in terms of daylight.

Although the two planets will be closest on Dec. 21, skywatchers can already start observing the two planets as they get closer to each other in the evenings leading to the event. As NASA explained, those who would like to watch this rare event unfold should simply look low in the southwest about an hour after sunset.