Seeing the light
Bible scholars believe that Christ was most likely born in September, so it may not have been so severe in Bethlehem, in the manger, among the oxen and asses.
Apparently the feast was moved closer to the winter solstice as a way of marrying existing religious practice from pre-Christian culture and as a happy metaphor for light coming into the world.
As we know, each passing day after Christmas gets a little longer. My grandmother used to say that the stretch in the evenings was equivalent to a cock's step.