Why is the winter solstice a very important solar term among the 24 solar terms?

From winter to the future, the direct point of the sun moves northward, the daytime in the northern hemisphere becomes longer, the sunrise time is advanced, and the sunset time is delayed; In the southern hemisphere, the days are shortened, the sunrise time is delayed and the sunset time is advanced.

Winter solstice, also known as "one-day birth", is an important solar term in the China lunar calendar and a traditional festival of the Chinese nation. The solstice in winter is commonly known as "Jiujiu, Winter Festival", "Long Festival" and "Ya Nian". As early as more than 2,500 years ago in the Spring and Autumn Period, China had observed the sun with earth gauges and determined the winter solstice, which was the earliest of the 24 solar terms, and the time was between June 65438+February 2 1 ~23 in the Gregorian calendar every year.