Right after sunset on the evening of December 21, 2020, Jupiter And the Saturn They will appear more closely together in Earth’s night sky than they have been since the Middle Ages, providing people around the world with a celestial remedy for ringing in the winter solstice.

“The alignments between these two planets are rather rare, they happen every 20 years or so,” said Rice University astronomer Patrick Hartigan. “But this conjunction is extremely rare because of how close the planets are to each other.” “You will have to return to pre-dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”

Jupiter and Saturn have been close to each other in Earth’s sky since summer. From December 16 to 25, the two will be separated by a diameter less than a full moon.

A view showing how the conjunction of Jupiter and Saturn will appear in a telescope directed towards the western horizon at 6 PM CST, December 21, 2020. Image adapted from graphics by the open-source planetarium software Stellarium. Credit: This work, ‘jupsat1’, is adapted from Stellarium by Patrick Hartigan, used under GPL-2.0, and made available under CC BY 4.0 with permission from Patrick Hartigan

“On the evening of the closest approach, on December 21, it will look like a double planet, separated by only 1/5 of the diameter of the full moon,” said Hartigan, a professor of physics and astronomy. “For most telescope viewers, every planet and many of their largest moons will be visible in the same field of view that evening.”

Although the best viewing conditions would be near the equator, the event would be visible anywhere on Earth, weather permitting. Hartigan said the planetary duo would appear low in the western sky for about an hour after sunset each evening.

“The further north the sights are, the less time they will have to peek at the conjunction before the planets sink below the horizon,” he said. Fortunately, the planets will be bright enough to be viewed at twilight, which may be the best time for many American viewers to observe the conjunction.

“By the time the sky gets completely dark in Houston, for example, the pairing will only be 9 degrees above the horizon,” Hartigan said. “This can be controlled if the weather is cooperative and you have an unobstructed view to the southwest.”

But an hour after sunset, people looking at the sky in New York or London will find the planets closer to the horizon, about 7.5 degrees and 5.3 degrees, respectively. He said that viewers there, and at similar latitudes, would do well to catch a glimpse of a rare astronomical sight as soon after sunset as possible.

Hartigan said those who prefer to wait and see Jupiter and Saturn close together and higher in the night sky will need to stay until March 15, 2080. After that, the pair will not appear like this until sometime after the year 2400.