On December 21, two enormous planets will align in a rare phenomenon known as a “Great Conjunction.” Jupiter and Saturn will orbit around the sun until they seem as if they have become one giant star. The last time this happened was March 4, 1226, making this a once-in-a-lifetime opportunity to see an astronomical wonder. It’s also a great outdoor holiday activity that can create a memory to last forever with the ones you love.
Don’t forget to look up at the sky tonight – it’s also the winter solstice – and catch sight of something no one currently on earth has ever experienced. This is a grand alignment that has not happened in eight centuries. When planets align in this particular way, it’s called a conjunction. While every 20 years Jupiter and Saturn appear to align as they orbit around the sun (their last conjunction was in 2000), the pair have never come anywhere as close as this to each other.
There’s no doubt this episode of Jupiter and Saturn’s heavenly dance is unique.
“This conjunction is exceptionally rare,” explained Rice University astronomer Patrick Hartigan, “because of how close the planets will appear to one another.”
In fact, these two gas giant planets will have a visible separation of only 0.1 degrees. We can only see this conjunction based on our point of view from Earth. In reality, the two planets remain millions of miles apart. However, this celestial display comes at a remarkable holiday time, causing some to harken the not-seen-since-the-Middle-Ages event as the “Christmas Star.”
Taking the time to see this amazing light will undoubtedly be worth it, and you won’t even need a telescope. All you need is a good viewing spot and to be on time, starting just before dusk December 21. Find a spot away from tall buildings or mountains, and as far from city lights as possible – and of course, you’ll need clear weather without clouds obscuring the sky. Look toward the low southwestern horizon right after the sun sets. The two planets will look like two strong points of light in the sky. Saturn, which is further away from Earth, will be slightly fainter. If you’re too early you might miss a fainter Saturn, and if you’re too late the two planets will have already slipped beneath the horizon for the night. Viewers closest to the equator will have the best viewing opportunity as there will be less time to catch a glimpse the further north you are. For most of North America, the ideal time is between dusk and 20 minutes after dark – and fortunately the planets will be bright enough to be viewed right at twilight.
If you do have a telescope, you’ll even be able to see some of the moons around each planet. With a typical amateur instrument set to low power, the two giant planets will fit within a single field-of-view. Jupiter, with its four bright moons, and Saturn, with its distinctive rings, will be visible all at once.
If the weather does not cooperate, there’s good news. Though the maximum conjunction is December 21 at 1:20 p.m. Eastern Time (when the sun is still out), Jupiter and Saturn will continue to appear closer than the diameter of a full moon until Christmas Day!
This is also a wonderful opportunity for parents to share the conjunction with their kids, as it won’t happen again March 15, 2080. Though 60 years from now is too far away for most adults to see it a second time, it is a perfect chance for children to remember their younger experience and look back fondly at their family.
“Astronomy gives you a different kind of perspective on the universe, which is different from our day-to-day experiences,” Hartigan added. “Things are going on above us all the time. They mark eras. [This event] is an important connection between generations.”This year’s conjunction is particularly special, not only for its appearance at the holidays but because these are the two furthest-away planets we can see from Earth with unaided eyes. Jupiter orbits the sun every 12 years, where Saturn takes about 30, meaning they meet every two decades, but this page in their celestial playbook brings them gorgeously close together just in time to celebrate the wonder of the holidays and the turn toward the rebirth of a new year. This is the solar system showing off in a magical display. Make sure to keep your eyes on the horizon Monday at nightfall.