This year's winter solstice comes with a nice bonus for sky watchers: Jupiter and Saturn will be so close they will look like a double planet on Dec. 21, reports Fox Science. In fact, earthlings haven't had a chance to glimpse the pair so close since the Middle Ages. "You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky," says Rice University astronomer Patrick Hartigan in a statement. Specifically, the planets will be separated by only a fifth of the diameter of a full moon. In astronomical terms, this meeting of the planetary giants is known as a "great conjunction," per Earth and Sky.
While Jupiter and Saturn come into alignment with each other every 20 years or so, it's the closeness of their 2020 encounter that is so unusual. The next time it happens will be in 2080. For those interested in glimpsing the phenomenon, the best time is probably about an hour after sunset, in the western sky, says Hartigan. "For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening," he says. Earth and Sky notes that there's no need to wait until the solstice to check out the planets, because they're relatively close already through the end of the year. (A moon of Jupiter glows in the dark.)