Tonight, if it’s not cloudy, look for two points of light huddled together in the night sky—one as bright as a star, the other slightly dimmer. Step outside an hour after sunset, stick a hand out, and cover them with your thumb. There, in the space of a fingertip, you’ll hold Jupiter, Saturn, and the many moons around them both.
Jupiter and Saturn come together like this in Earth’s night sky only once every 20 years, when the orbits of all three planets align. From our perspective, the giant planets have journeyed together across the evening sky all year. In the past few weeks, they’ve appeared a tiny fraction of a degree closer every night, like a cosmic stop-motion animation.
“They’re so bright and very easy to pick out in the night sky,” says Amanda Bosh, a planetary scientist and operations manager at Lowell Observatory in Arizona, one of the oldest observatories in the country.
The meeting of the solar system’s biggest planets will be visible from just about anywhere on Earth. This conjunction coincides with the winter solstice in the Northern Hemisphere, but it is special for another reason, too: The last time anyone on Earth experienced such a sight was 800 years ago.
Saturn takes longer than Jupiter to orbit the sun, so every two decades, Jupiter catches up to it, a phenomenon that astronomers call a “great conjunction.” Some conjunctions appear cozier to us than others, thanks to differences in the big planets’ orbits from our own. The last time Jupiter and Saturn showed up this close together in the sky was in 1623, but the planets were near the sun then, so by the time it dipped below the horizon, they had gone with it. The last time the planets appeared this close and could be seen from the ground was in 1226.
That year, when construction of the Notre-Dame cathedral was still under way in Paris, the two planets were visible just before dawn. “You may very well have had artisans that were working on the stained glass that were going to work in the morning, looking up, and seeing it,” Patrick Hartigan, a physics and astronomy professor at Rice University, told me. Would they have noticed, as they stepped outside each morning, that the pair of milky-white points overhead had moved closer together with each passing day?
The great conjunctions of Jupiter and Saturn are some of the oldest observations in history, and they have long been associated with big and meaningful events: the ends of empires, the rise of new dynasties, chasmic cultural shifts. “From time immemorial, people have looked to the stars to help them explain the chaos of their present and the uncertainty of their future,” Ali A. Olomi, a history professor at Penn State who has studied how early observers thought about planetary conjunctions, told me. Thirteenth-century Muslim writers, for example, believed that the 1226 conjunction foretold the arrival of the Mongols in China. “By 1226, the Mongols were already on the scene, so they’re reading the writing on the wall, but they’re giving significance to those changes by saying, look, this was ordained by the stars,” Olomi said.
Reading about tonight's event—a cosmic conjunction to end this year, of all years—and jumping to making meaning out of it might be tempting. That tendency has sharpened for many of us in 2020, and when unusual news has come out, especially anything related to the cosmos, we’ve treated it as a reflection of these months that sometimes seemed to exist out of time. The discovery of a black hole near Earth back in May seemed like some kind of sign. So did that monolith in Utah that seemed to come out of nowhere. The rareness of this conjunction will likely prompt some similar shivers.
Because while we certainly know a lot more about Jupiter and Saturn today than anyone did 800 years ago, the desire to draw meaning from celestial bodies and apply it to earthly matters hasn't disappeared. The instinct is hardwired; it’s why we see animals in the shapes of cumulus clouds, faces in the craters on the moon—and meaning in two bright planets in the night sky. In moments of crisis and anxiety, the urge to find explanations everywhere is particularly strong. It’s one reason that astrology has seen such a resurgence among Millennials in the past decade; as my colleague Julie Beck has written, people tend to turn to the zodiac in times of stress. “We’re always trying to look for meaning, and that’s something that doesn’t change, whether we’re talking about the 12th century or the 21st century," Olomi said.
For Jeffrey Hunt, an astronomy educator in Illinois who tracks conjunctions, their meaning is simple enough: Time is passing, generation by generation. He recently told one of his young grandsons about the Voyager missions, using as reference a model of the solar system they had painted on the sidewalk near their house. In the 1970s, NASA took advantage of a rare cosmic alignment to visit the planets of our solar system. It took two years to reach Jupiter, another year to reach Saturn, and another six to reach Uranus. By the time the mission reached Neptune, 12 years had elapsed. When Hunt told his grandson that great conjunctions come along every 20 years, the child gave him a strange look. To a 9-year-old, two decades might seem almost as unfathomable as the millions of miles that separate Jupiter and Saturn. “It was an interesting response, to see a 9-year-old look at you and wonder whether you’re telling the truth,” Hunt told me.
Tonight, he will go outside, not long after sunset, to find the planets—so close they seem to be nearly touching—before they fade later in the night. “As Earth turns and those planets get lower in the sky, they’ll be more difficult to see,” Hunt said, especially if buildings or trees block your horizon. But these conjunctions are some of the most accessible in all of astronomy. For many of the most dramatic shows in space, people have to be in the right place at the right time—like last week’s solar eclipse, which cast a shadow on Chile and Argentina. This summer, when a comet, one of the brightest in decades, whizzed past Earth, residents of the Northern Hemisphere got the best view. Even then, many needed binoculars to spot the comet, which won’t appear again for another 6,800 years.
This year’s rare planetary alignment may not be a harbinger from the heavens, but it is a pleasant distraction. The conjunction won’t resemble a biblical, blazing star, as some news reports have suggested, but the sight might provide a little dose of awe nonetheless. And the experience of awe, psychology research has shown, can actually prompt feelings of connectedness with other people—something this year could use, conjunction or not. Tomorrow, Jupiter and Saturn will start moving away from each other, tracing their own paths through the solar system. They will hover lower in the sky, and by early next year, vanish into the sun’s glare.