December 21 marks the Winter solstice in northern hemisphere and is the shortest day and longest night of the year. The exact opposite happens in the southern hemisphere.

According to astronomers, on the night of December 21, Jupiter and Saturn will appear so closely aligned in the southern/southwestern sky that they will look like a double planet. This close approach is called a conjunction. The fact that this event is happening during the winter solstice is pure coincidence, according to NASA.

They say the 2020 great conjunction of Jupiter and Saturn will be the closest since 1623 and the closest observable since 1226.

This year’s extra-close Jupiter-Saturn conjunction won’t be matched again until March 15, 2080.