What is the reason why there are two solar terms in the song dynasty every month?

There are two solar terms in each month in the first half of the year. The former is around the 6th, and the latter is around the 2nd1,with a difference of 1~2 days. There are two festivals every month in the second half of the year, the first one is around the 8th, and the second one is around the 23rd, with a difference of 1~2 days.

"Twenty-four solar term song" is a small poem compiled for the convenience of remembering the twenty-four solar terms in the ancient calendar of China, and there are many versions circulating. Solar terms refer to the 24 solar terms and climate. It is a calendar made in ancient China to express seasonal changes and guide farming. It is the crystallization of the long-term experience and wisdom of the ancient working people in China.

Because the lunar calendar in China is a kind of "yin and yang calendar", which is based on the movement of the sun and the moon, it can't fully reflect the solar cycle. But China is an agricultural society, and agriculture needs a strict understanding of the movement of the sun, so farming is entirely based on the sun. Therefore, the "twenty-four solar terms" that reflect the solar cycle alone are added to the calendar as the standard for determining leap months.