On December 21, 2020, the two gas giants in the solar system will appear together in Earth’s night sky more than they have been since 1226 AD.
On December 21, Jupiter and Saturn will appear only a tenth of a degree apart. This means that the two giant planets and their moons will be visible in the same field of view through binoculars or a small telescope.
In fact, Saturn will appear near Jupiter like some Moons of Jupiter. This event is called a “big link.”
This happens every 20 years in this century as the orbits of Earth, Jupiter and Saturn are periodically interconnected, making these two outermost planets appear close to the night sky.
Nevertheless, this is the “greatest” significant association between Jupiter and Saturn over the next 60 years, as the two planets did not appear that close to the sky until 2080.
Professor Patrick Hartigan, astronomer at Rice University, said: “The alignments between these two planets are rather rare. They happen every 20 years or so, 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.”
He added, “On the evening of the closest approach, on December 21, the planet will look like a double planet, separated by only 1/5 of the diameter of the full moon.”
“For most telescope viewers, every planet and many of their largest moons will be visible in the same field of view that evening.”
Jupiter and Saturn will appear low in the western sky for about an hour after sunset each evening.
Professor Hartigan said: “The further north the sights are, the less time they will have to peek at the connection before the planets sink below the horizon.”
“Fortunately, the planets will be bright enough to watch in 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.”
“It would be possible to control viewing this if the weather cooperated and you had an unobstructed view to the southwest.”
“But an hour after sunset, people looking toward the sky in New York or London will find the planets closer to the horizon, about 7.5 degrees and 5.3 degrees, respectively.”
“It is best for viewers there, and at similar latitudes, to catch a glimpse of a rare astronomical sight as soon as possible after sunset.”
“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.”
“Then, the duo would not make such an appearance until sometime after the year 2400.”
This article is based on text provided by the National Aeronautics and Space Administration and Rice University.