What's the tenth day of winter?

The first 10 day of the winter month is 65438+February 5th.

According to the lunar calendar, the solar term from the winter solstice must appear in 1 1 month. If the operation is improper, there will usually be a leap month to adjust, which is just a rule. Because for ancient surveying techniques, the altimeter shadow method is the simplest and most reliable means to determine the tropic year. For the northern hemisphere, the winter solstice surface shadow is the longest, and the measurement accuracy is the most guaranteed. It is most suitable as a calendar coordinate point (although the summer solstice is the shortest, the shadow length is too short, the measurement error is large, and it is inconvenient due to precipitation problems).

But in the early days, different dynasties and vassal States chose the first month differently. Some build children, that is, the first month is in February (the month in which winter is located), some build ugliness (the first month after February), and some build shade (February after February). (As for Qi, it involves the setting of leap month. Every other month in the 24 solar terms is qi, and the month without qi is last month.

Because Yin Jian's words were close to beginning of spring in the first month, which was suitable for guiding agricultural production, Emperor Wu of the Han Dynasty promulgated "taichu calendar" and kept Yin Jian in our calendar.