When did the weather start? The days get longer and longer.

The weather starts from the winter solstice and the days get longer and longer.

The solstice in winter is the day when the sun reaches the tropic of Capricorn. The shortest day and the longest night. After the solstice of winter, the days become longer and longer, and after a period of cold, the weather becomes warmer and warmer. Therefore, since the Xia Dynasty, people have taken the winter solstice as the starting point of solar terms.

At the latest in Shang Dynasty, China people had already used the method of "measuring ruler shadow" to measure the time of solstice, but there would be an error of two to three days. In history, He Chengtian once "set up an eight-foot platform and measured it for more than ten years", and Zu Chongzhi once "measured the shadow for several years and looked up".

Pay attention to the winter solstice, because the winter solstice and summer solstice are the key to making a calendar, and the calendar is accurate. Measurement can prove that the emperor has mastered the destiny and is qualified to meet the needs of heaven, so he attaches great importance to it. In the Zhou Dynasty, the annual winter solstice was New Year's Day.

The Duke of Zhou stipulated in Zhou Li that "winter is the day to send ghosts and gods" and "the five emperors, the sun, the moon and the stars are in the suburban altar". There are also folk activities in the suburbs that make use of the winter solstice to worship heaven.

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