Corresponding to the twenty-four solar terms

The twenty-four solar terms are determined by the working people of our country according to the position of the sun running on the ecliptic and the ground climate change caused by it. People divide the ecliptic into twenty-four segments, and it is determined that every time the sun runs 15 degrees, it is a solar term starting from the longitude zero of the vernal equinox. The 24 solar terms are: beginning of spring, rain, fright, spring equinox, Qingming, Grain Rain, Changxia, Xiaoman, Mangzhong, Summer Solstice, Slight Summer, Great Summer, beginning of autumn, Summer Dew, Autumn Equinox, Cold Dew, First Frost, beginning of winter, Light Snow, Heavy Snow, Winter Solstice, Slight Cold and Great Summer. Twenty-four solar terms in Song Dynasty: "Spring rains shake the spring and clear the valley, and summer is full of heat;" Autumn, autumn frost, winter snow, winter cold; There will be 621 in the first half of the year and 823 in the second half. " The last two sentences are used to calculate the date of solar terms. Generally speaking, the solar terms in the first half of the solar calendar are around the 6th and 2nd1of each month. The second half of the year will be around the 8th and 23rd. The twenty-four solar terms are unique in our calendar. They became the main basis of agricultural production activities as early as the Qin and Han Dynasties, and have been in use ever since.

In addition, solar terms reflecting cold and hot are determined by the law of the earth's movement around the sun, and have nothing to do with the movement of the moon, so solar terms actually belong to the solar calendar category. But many people don't understand this truth, thinking that solar terms are the lunar calendar. In fact, as long as we pay attention to the dates of solar terms in the solar calendar and the lunar calendar, it is not difficult to see that the dates of solar terms in the lunar calendar are very different, but there are almost fixed dates in the solar calendar, and the difference between them will not exceed one or two days.

From one solar term to the next, it is called "solar term month". Because the earth moves around the sun in an elliptical orbit instead of a perfect circle, its speed is fast and slow. The speed near the slight cold is fast and the "moon festival" is short. Before and after the summer heat, the speed is the slowest and the "solar term month" is the longest. An average solar month is one twelfth of the tropical year, which is about 30 days 12 hour.