“A Christmas Star” might sound like the name of a really bad Hallmark movie, but it’s a real astronomical phenomenon, and it’ll appear in the night sky this month.

When Jupiter and Saturn align so closely in the night sky that they appear to collide, creating a point of light, it’s called a “Christmas star” or “star of Bethlehem.” It hasn’t happened since March 4, 1226, but lucky for us it’s happening this year on December 21.

The nickname “Christmas star” comes from the belief that the “star of Bethlehem” in the story of the three wise men was nothing more than the scenic and rare alignment of Jupiter, Saturn, and Venus.

Patrick Hartigan, astronomer at Rice University in Texas, told Forbes, “Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to be to one another.”

The event technically occurs every 19 to 20 years, but this is the closest the planets will look to us from Earth since the 13th century. To see it, look toward the southwest about 45 minutes after sunset on December 21. It will also be visible for about one hour after sunset in the northern hemisphere for the whole fourth week of December.

The next occurrence of such an alignment isn’t expected to take place until 2080.