When something inordinately rare or unexpected happens, it is said âthe planets aligned.â
On Dec. 21, the winter solstice, two planets will appear nearly aligned, resulting in an event so uncommon itâs befitting of the saying. At one time, astronomers may have felt it so closely resembled a Christmas miracle â or, perhaps, the star of Bethlehem â that they named the spectacle the âChristmas Star.â
The event is called a conjunction, said Shane Larson, associate director of Northwesternâs Center for Interdisciplinary Exploration and Research in Astrophysics.
âConjunctions of Jupiter and Saturn happen every 20 years and most arenât very close at all. Whatâs special this year is theyâre right, right next to each other,â said Larson. âThese two planets have never been this close in the sky for 400 years so no one really knows what itâs going to look like because it hasnât happened since 1623, in Galileoâ