Because of this "the winter solstice is the birth of Yang [or the sun]." What is interesting is that the ancient civilizations of the West began the new year at the vernal equinox, but the ancient Chinese started counting the new year from the winter solstice.
有趣的是，西方文明古國多以「春分」為一年的起始，中國早年卻是以「冬至」為歲首。