On December 21, humans can witness something they haven’t seen in nearly 800 years.

That’s right, during the upcoming winter solstice, Jupiter and Saturn will line up to create what is known as the “Christmas Star” or “Star of Bethlehem.”

These two planets have not appeared (relatively) close to the Earth’s vantage point since the Middle Ages.

“The alignment between these two planets is rather rare, occurring once every 20 years or so, but this pairing is extremely rare due to how close the planets are to one another,” said Patrick Hartigan, astronomer at Rice University, Forbes said. “You will have to go back to before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”

Northern hemisphere stargazers must turn their heads and telescopes to the southwestern part of the sky about 45 minutes after sunset to see the planets on December 21.

According to Forbes, Seeing stars of this size will not happen again until 2080.