The event has not been seen with the naked eye since 1226.

With all the magical light shows that winter brings to Chicago, it’s easy to forget that the sky provides some stunning celestial light shows of its own. Astronomers have been spoiled of late with the blazing fireballs of the Leonid Meteor Shower in November and the incredible Geminid Meteor Shower earlier this month.

Thanks to the paths of Jupiter and Saturn, the skies have one last remarkable astronomical event for us before the year is out, and unlike the aforementioned meteor showers, you have to roll back nearly 800 years to find the last time we were treated to such an occasion.

The astronomical event, known as the “Great Conjunction”, happens once every 20 years when the orbits of Earth, Jupiter, and Saturn cause the two gas giants to shine brightly as a “double planet.” According to NASA, Jupiter takes 12 years to orbit the sun while Saturn’s orbit takes 30 years and so every couple of decades, Saturn is lapped by Jupiter.

This month on Monday, December 21, the two planets will come extremely close to one another in an event that hasn’t happened since medieval times on March 4, 1226. According to the Adler Planetarium, the double planet will be visible in the skies as early as Wednesday, December 16 and Thursday, December 17, but it will be at its most spectacular on the evening of December 21.

For Christians observing the holiday, the event, sometimes called the ‘Christmas Star’, holds even more meaning. Jupiter and Saturn’s alignment is theorized to be the ‘Star of Bethlehem’ that the three wise men followed on Christmas Eve in the biblical text. The ancient Magi supposedly came across the newly born Jesus Christ directly below where the star stopped.

The Bible’s mention of the “Star of Bethlehem” has long obsessed astronomers and theologians but it is commonly believed to be the result of an extremely rare alignment of planets such as the one we will be treated to later this month, and one that may never happen again.

[Featured image from Shuttershock]

See more: 22 Wonderful Things To Do In Washington DC This December