Once every 20 years, the two largest planets in our solar system—Jupiter and Saturn—appear to meet in Earth’s skies.
This “Great Conjunction” happens next on December 21, 2020, but this time, Jupiter and Saturn will be closer than they’ve been in nearly 400 years.
December 21 also happens to be the night of the winter solstice, and the peak of the Ursid meteor shower.
For most Great Conjunctions, Jupiter and Saturn are separated by about 1 degree, which is the width of two full moons in the sky.
This year, they will be separated by just one-tenth of a degree, which is one-fifth the size of the full moon.
A Great Conjunction happens every 20 years, but the last time Jupiter and Saturn were this close was the year 1623.