photo by: Associated Press

People are silhouetted against the sky at dusk as they watch the alignment of Saturn and Jupiter, Monday, Dec. 21, 2020, in Edgerton, Kan. (AP Photo/Charlie Riedel)

Jupiter and Saturn merged in the night sky Monday, 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 this one 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, weather permitting.

photo by: Associated Press

Saturn, top, and Jupiter, below, are seen in the sky, Monday, Dec. 21, 2020, above Edgerton, Kan. (AP Photo/Charlie Riedel)

photo by: Associated Press

People are silhouetted against the sky at dusk as they watch the alignment of Saturn, top, and Jupiter, Monday, Dec. 21, 2020, in Edgerton, Kan. (AP Photo/Charlie Riedel)

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.

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

Saturn and Jupiter had been drawing closer in the south-southwest sky for weeks. Jupiter — bigger and closer to Earth — is vastly brighter.

“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.

photo by: Associated Press

A statue of a Kansa Indian atop the Kansas Statehouse stands in the foreground as Saturn, top, and Jupiter, below, are seen Saturday, Dec. 19, 2020 in Topeka, Kan. (AP Photo/Charlie Riedel)

photo by: Associated Press

A statue of a Kansa Indian atop the Kansas Statehouse stands in the foreground as Saturn, top, and Jupiter, below, are seen Saturday, Dec. 19, 2020 in Topeka, Kan. (AP Photo/Charlie Riedel)