《淮南子·天文训》
如果冬至壬午日，那么甲子受命起行主管春季，这时木气为主宰，火烟呈青色。
壬午冬至，甲子受制，木用事，火烟青。
If the winter solstice is Renwu day, then Jiazi will be assigned to lead the spring, at this time, the wood energy dominates, and the smoke will be green.