Tonight, on December 21, Jupiter and Saturn are putting on a show.

The two planets are coming so close together that they will look like one, bright light source, known as a "Christmas Star".

It's a great opportunity to teach kids about science, as this is something that hasn't happened in 800 years.

"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," Patrick Hartigan, an astronomer at Rice University, told Forbes. "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."