In this month, the winter cold tightens its grip, and the nights are at their longest and darkest. This full moon often comes before Christmas and so was sometimes called the moon before yule.

Among other tribes, this was called the long nights moon, a doubly appropriate name since the midwinter nights are indeed very long, and the moon is also above the horizon a long time. The full moon in midwinter has this high trajectory across the sky because it is opposite to the low sun.