In December, Jupiter, Saturn will look like a double planet for the first time since the Middle Ages

Just after sunset on the evening of December 21, Jupiter and Saturn will appear closer to each other in Earth’s night sky than they have been since the Middle Ages, offering people of the world whole heavenly treat to ring at the winter solstice.

“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare due to the closeness of the planets to each other,” the astronomer said. Rice University, Patrick Hartigan. “One would have to go back to the dawn of March 4, 1226 to see a closer alignment between these objects visible in the night sky.”

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

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

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

“The farther north a viewer is, the less time they will have to see the conjunction before the planets sink below the horizon,” he said. Fortunately, the planets will be bright enough to be seen at dusk, which may be the best time for many American viewers to observe the conjunction.

“By the time the sky is completely dark in Houston, for example, the conjunction will be just 9 degrees above the horizon,” Hartigan said. “It would be manageable if the weather permitted and you had a clear view to the southwest.”

But an hour after sunset, people looking skyward in New York or London will find the planets even closer to the horizon, around 7.5 degrees and 5.3 degrees, respectively. Viewers there, and in similar latitudes, would do well to get a glimpse of the rare astronomical sight as soon as possible after sunset, he said.

Those who prefer to wait and see Jupiter and Saturn this close together and higher in the night sky will have to stay until March 15, 2080, Hartigan said. After that, the pair won’t make such an appearance until after 2400.