The winter solstice was anciently called tiānzhèng — the moment when yang energy is first reborn.
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history
Ancient dynasties disagreed over which lunar month started the year. Zhou began its calendar at the winter-solstice month (天正, 'heaven's first'), Shang at the following month (地正), Xia at the one after (人正) — the Xia system survives in today's 农历.