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See it again: Jupiter and Saturn had their Great Conjunction on Dec. 21, 2020

Jupiter and Saturn appeared closer to each other than they had since the 1600s.

Jupiter and Saturn merged in the night sky on Dec. 21, 2020 for the "Great Conjunction," appearing closer to one another than they have since Galileo’s time in the 17th century. 

Astronomers say so-called conjunctions between the two largest planets in our solar system aren't particularly rare. Jupiter passes its neighbor Saturn in their respective laps around the sun every 20 years.

But the one last year was especially close: Jupiter and Saturn were just one-tenth of a degree apart from our perspective or about one-fifth the width of a full moon. They were easily visible around the world a little after sunset, if local weather permitted.

For those who couldn't see it, the Lowell Observatory in Arizona livestreamed the conjunction, which can be seen in the player above.

Toss in the winter solstice in the Northern Hemisphere, the longest night of the year — and the summer solstice in the Southern Hemisphere — and this just-in-time-for-Christmas spectacle promised to be one of the greatest of Great Conjunctions.

“What is most rare is a close conjunction that occurs in our nighttime sky," said Vanderbilt University’s David Weintraub, an astronomy professor. "I think it’s fair to say that such an event typically may occur just once in any one person’s lifetime, and I think ‘once in my lifetime’ is a pretty good test of whether something merits being labeled as rare or special.”

It was the closest Jupiter-Saturn pairing since July 1623, when the two planets appeared a little nearer. That conjunction was almost impossible to see, however, because of its closeness to the sun.

Credit: AP
Saturn, top, and Jupiter, below, are seen in the sky, Monday, Dec. 21, 2020, above Edgerton, Kan. The two planets are in their closest observable alignment since 1226. Appearing a tenth of a degree apart, the alignment known as the "great conjunction" has also been called the "Christmas Star." (AP Photo/Charlie Riedel)

Considerably closer and in plain view was the March 1226 conjunction of the two planets — when Genghis Khan was conquering Asia. The 2020 conjunction was the closest pairing that was visible since way back then.

“I love watching them come closer and closer to each other and the fact that I can see it with my naked eyes from my back porch!” Virginia Tech astronomer Nahum Arav said in an email.

Despite appearances, Jupiter and Saturn were actually more than 450 million miles apart. Earth, meanwhile, was 550 million miles from Jupiter.

Their next super-close pairing: March 15, 2080.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.