12/24/2020 – Ephemeris – Was the Star of Bethlehem a triple conjunction of Jupiter and Saturn in 7 BC?

This is Bob Moler with Ephemeris for Christmas Eve, Thursday, December 24th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:07, and it will rise tomorrow at 8:18. The Moon, 3 days past first quarter, will set at 3:50 tomorrow morning.

For many years the most popular theory for the origin of the Star of Bethlehem was a triple conjunction of Jupiter and Saturn in 7 BC. This is because, due to Earth’s motion, other planets from our view point seem to reverse course when we pass them or are being passed in the circular racetrack of the solar system. When Jupiter and Saturn approach each other just before they go retrograde or reverse course they have a chance to pass each other, backup and pass again, then going forward to pass a third time. Jupiter and Saturn did that last in 1981, so it’s a reasonably rare occurrence, especially when it happens in front of the constellation Pisces which was supposedly related to the Jews.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Jupiter and Saturn pass each other three times from May to December in 7 BC against the constellation of Pisces. Reload the page to replay the animation. Created using Cartes du Ciel (Sky Charts) and GIMP.

Retrograde motion illustrated using Mars in 2018. Created using my LookingUp program.