Residents of Scott County may have noticed a brighter-than-usual star in the sky Monday night, but may not have known that what they saw is the “Christmas star,” though it’s not a star at all.
For the first time in nearly 800 years, the planets Jupiter and Saturn aligned in the night sky to be visible to nearly everybody with the naked eye for what is called a “great conjunction.” These two planets coming together is what creates the illusion of the star.
Dr. David Bowman, professor emeritus of physics at Georgetown College, said the conjunction set Monday evening two hours after the sun.
“That means only from after it gets dark enough to see the planets until about 7:20 p.m. (was) the conjunction visible, if clouds didn’t obscure the lower southwestern sky,” Bowman said.
Gary Ferland, physics and astronomy professor at University of Kentucky, said the best way to explain a conjunction is to envision yourself driving down the road.
“The Earth goes around the sun and we look out at other planets in the solar system, and we see it from our perspective on the Earth,” he said. “It’s like you’re driving in a car on the highway and there’s a water tower visible. If you’re driving faster than everybody, you can go faster than the car in the right lane. You might look at it once when the car’s in front of the water tower, but along the side it might look like the car’s lined up with the water tower.”
According to NASA, these types of conjunctions happen roughly every 20 years when Jupiter overtakes Saturn in orbit, but what makes this a “great conjunction” is that this is first time in 400 years the two planets have passed this close together.
“This one is special because, at 1/10th of a degree apart, they won’t be this close again for multiple centuries,” Bowman said. “And it is happening on the date of the December solstice, which makes it especially rare.”
It’s also been almost 800 years since this conjunction occurred at night, according to NASA.
“The previous great conjunction between Jupiter and Saturn was about 400 years ago, but it wasn’t visible from Earth because they were almost directly behind the sun when it happened and they can’t be seen in the daytime when looking directly at the sun,” Bowman said.
The two planets have been visible from the sky for over one week, but the point where the two are at their absolute closest during this conjunction was Dec. 21. This makes it visible and appear as the famed “Christmas star.”
“The association with Christmas is simply because it is happening in late December at Christmastime,” Bowman said. “Some people believe that the original Christmas star, recorded in the Gospel of Matthew, was a triple conjunction between Jupiter and Saturn. Others believe it was something else such as a triple conjunction between Jupiter and Venus, Saturn and Venus, a supernova, nova or a comet.”
Residents of Georgetown were able to see the culmination of the conjunction Monday night.
“It’s visible from here,” Ferland said. “Just go out in your backyard. You don’t even need a dark sky really. A conjunction like this, Jupiter and Saturn are just about the brightest lights in the sky. If you look around, you will definitely notice the two.”
Ferland said this is an exciting event for him as it reminds him why he got interested in astronomy as a child.
“It’s interesting, from my own perspective,” he said. “My father was in the Air Force, and I always wanted to be in the Air Force or an astronaut. Apollo happened when I was a teenager. It just always got me looking at the sky. There’s a sort of romantic connection with what’s in the sky.”
Ferland said he recommends star-gazers download one of the many apps available to assist with locating constellations and future conjunctions. Android users can download Sky Map for free from Google Play while Apple users can download a free or paid version of SkyView. These apps use your location to give you an accurate look at what can be seen in the star at all times.
Kyle Woosley can be reached at firstname.lastname@example.org.