This Christmas there will be an astronomical phenomenon that has not occurred for the past 800 years. On Dec. 21, Jupiter and Saturn will come into such close alignment that they will appear to be a unit, calling to mind the “Christmas star” the Magi followed to find the newborn Messiah.
“Alignments between these two planets are rather rare, occurring once every 20 years or so,” Patrick Hartigan, astronomer at Rice University, told Forbes, “but this conjunction is exceptionally rare because of how close the planets will appear to be to one another. 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.”
When celestial bodies pass or appear to meet in the sky, astronomers call the event a “conjunction.” Even though Jupiter and Saturn experience a conjunction once every 19.6 years, they will not come into this close of an alignment again until March 15, 2080.
A Christmas Star on the Darkest Day of the Year
The day the “Christmas star” will appear happens to be the Northern Hemisphere’s winter solstice, which is the day of the year when the North Pole is tilted the furthest away from the sun. This is also the shortest and darkest day of the year for those living in this hemisphere.
The conjunction of the two planets will be visible to the naked eye everywhere on Earth, assuming local weather does not obscure it. People should look for the “Christmas star” in the southwestern part of the sky near the horizon for about an hour after sunset. That is when it will be brightest, although the conjunction might be visible at other times that week. Those viewing the phenomenon through telescopes will be able to see each of the two planets, as well as some of their moons.