Jupiter and Saturn will align in the night sky on Monday. It’ll be the closest they’ve appeared in 800 years.
The two planets move into alignment, or conjunction, every 20 years. But this year they will be so close that they’ll look like a “double planet.”
The last time Saturn and Jupiter were both this close and visible was in 1226.
Here are the best ways to see, photograph, or watch a live stream of the conjunction.
Jupiter and Saturn are about to line up perfectly in the night sky, getting so close on December 21 that they’ll seem to touch.
The last time they looked this close from Earth’s vantage point was nearly 800 years ago, on March 4, 1226.
An astronomical event in which celestial bodies align is called a conjunction. Since this conjunction involves the two biggest gas giants in our solar system, it’s known as the great conjunction. It happens to some degree once every two decades.
“But it is fair to say that this conjunction is truly exceptional in that the planets get very close to one another,” Patrick Hartigan, a professor of physics and astronomy at Rice University, explained on his website.
He added, “In fact, they will be so close it may be a challenge to separate them with the unaided eye for many people.”
Here’s how to see this rare conjunction.
How to view a ‘double planet’
Jupiter and Saturn are actually separated by more than four times the distance between Earth and the sun.
But on the night of the winter solstice, they will be separated in the sky by a distance equal to about one-fifth of a full moon’s diameter, according to Hartigan. That’s so close that the two points of light will look like they form a double planet. According to NASA, a pinkie finger at arm’s length should easily cover both Jupiter and Saturn in the sky.
Viewed through a small telescope, Jupiter and Saturn should appear in the same field of view, along with some of their moons.
For viewers in the United States, Canada, and Europe, it could be challenging to see this conjunction because of how low it will be on the horizon in the Northern Hemisphere, Hartigan said.
“Viewing conditions are best close to the equator, though no matter where you are there is maybe an hour or so to observe this conjunction before the planets sink into the haze,” he added.
To catch a glimpse, head out around twilight – the hour after sunset – and point your telescope toward the southwestern sky. (Websites like Stellarium can help you orient your telescope.)
“You will need to have a clear southwestern horizon and no low clouds in the distance,” Hartigan said.
He recommends setting up your telescope before it gets dark and bringing binoculars, which could help you spot Jupiter’s four moons too.
If it ends up being cloudy on the night of the solstice, don’t worry, Hartigan said. The conjunction is an ongoing event from December 17 to 25 – December 21 is just when the two planets will be the closest in the sky.
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” Henry Throop, a NASA astronomer, said in a press release. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
You could photograph the conjunction with your phone
Jupiter and Saturn’s conjunction “can be photographed easily on DSLR cameras and many cell phone cameras,” NASA said.
The agency suggests using the “night mode” feature on an iPhone, Pixel, or Galaxy to get a stable, long-exposure photo.
“Try to frame the planets with something – the silhouette of a tree, an outdoor landscape, the arch of a building, or even a neon sign,” NASA said.
If you use a DSLR camera, a tripod is recommended to get good long-exposure photos. In the absence of a tripod, set your camera to a shutter speed of less than one-quarter of a second. Also be sure to open your camera’s aperture to its widest setting and use manual focus mode, NASA said.
For people who can’t head outside for the event, the Lowell Observatory in Flagstaff, Arizona, will host a YouTube livestream of views through its telescopes starting at 7 p.m. ET on December 21. In Rome, the Virtual Telescope Project also plans to share live views of the conjunction.
Another conjunction like this will come in 2080
In the last 2,000 years, there were just two times that Jupiter and Saturn came closer in the sky than they’ll get this year. One was in 1623, but the sun’s glare made it impossible to see. The other was in 1226.
But if you miss this upcoming conjunction, another will come in 60 years.
On March 15, 2080, Jupiter and Saturn will look just as close as they do this year. That event will be easier to see, since it’ll appear higher above the horizon, Hartigan said.
“The major challenge there is you’ll have to stay alive for another 60 years to see it!” he added.
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