Every 20 years, Saturn and Jupiter pass each other like ships in the night sky. When they do, we call it a ‘Great Conjunction’ because it’s by far the rarest of the conjunctions between planets we can see with the naked eye. It last happened in December 2020 and lasted for two weeks.

During this time, Jupiter and Saturn were the closest they’ve been since 1623, back when Galileo was still alive, a little more than a decade after he first used a telescope to discover Jupiter’s four largest moons that now collectively bear his name. The Great Conjunction of 2020 was also the closest observable one for 800 years. So, if you missed it, that’s too bad - you’ll be waiting a while for the next one.

Johannes Kepler observed that a similar conjunction would have occurred in 7 BCE, hence the theory that it was the famous “Christmas Star” that guided the three wise men in the Biblical story about the birth of Jesus Christ.

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