Skywatchers and those who celebrate Christmas will be certain to enjoy a celestial event Monday evening when Jupiter and Saturn will appear to meet up forming one star on the winter solstice — an event people are commonly calling the “Christmas Star.”
According to NASA, what is formally called the “Great Conjunction” of the two planets was first discovered by Italian astronomer Galileo Galilei in 1623, 13 years after he had discovered Jupiter’s four moons and Saturn’s ring.
And that was the last time anyone has witnessed such a near alignment.
Locally, the best chance to see the star will be at twilight — just after the sun sets from about 5:30 to 6:15 p.m. — on Monday, according to Kathryn Devine, physics professor at College of Idaho in Caldwell.
The planetary duo have been visible all summer, but not this close together.
“They have been doing this little dance all summer long, and have been noticeably closer since late summer,” Devine said.
It is noteworthy, however, that if you had taken a trip to Mars or the International Space Station or anywhere else in space for that matter, that you wouldn’t see the “Great Conjunction.” The viewing of the Christmas Star is reserved solely for earthlings.
“What’s happening is from our point of view on Earth,” Devine said.
She said while looking up toward from Earth, they will be in just the right position along our line of site.
“Looking at the night sky, they will appear at the same point in a beautiful alignment of Earth, Jupiter and Saturn around their point of the sun,” Devine said.
She explained that the planets will not be precisely aligned however — as that is physically impossible due to their own tip in the orbital path. Those using a telescope or a pair of binoculars, such as those used to watch birds, will be able to notice the planets will be one-tenth of a degree apart, with Jupiter in front of Mars. The “Christmas Star” will still be visible to the naked eye.
For Devine, Monday will be a special celebration indeed as she has stakes from a professional and personal information, as it is also her birthday. She and her brother were born two years apart on the exact same day. As such, celebrating winter solstice at her house has always been special.
“I’m not a big fan of the short daylight, so I’m always like, ‘OK, this is the worst it gets,’” Devine said of the solstice shifting us back to longer days.
According to NASA, what makes this spectacle so rare is not only that it’s been 400 years since they passed this close to each other in the sky, it’s been nearly 800 years since it happened at night.
Devine urges people not to wait until too late to see the celestial phenomenon which isn’t expected to happen again for another couple hundred years.
“Go out in the early evening — if you wait too long it will set,” she said, noting that the planets are so bright they will be visible before the stars themselves start to pop up.
So long as there aren’t a lot of clouds, the planetary alignment should be easy to see, as the moon is also being “very cooperative” for stargazing at this time, Devine said. It is a crescent, keeping the sky dark and stars easy to view.
NASA reminds viewers to find a spot with an unobstructed view of the sky, such as a field or park.
“We’ve got this really ice opportunity right when the sun goes down, before it gets too cold outside and before the kids go to bed,” Devine said. “It’s a good way to celebrate the days getting longer and the nights getting shorter.”