Division of day and night length of 24 solar terms

The length of the 24 solar terms is divided according to the position of the sun on the ecliptic (that is, the orbit of the earth around the sun).

Twenty-four solar terms reflect the natural phenomenon and seasonal characteristics of farming in a certain area of China (represented by the middle and lower reaches of the Yellow River). That is, beginning of spring, Rain, Surprise, Vernal Equinox, Qingming, Grain Rain, Changxia, Xiaoman, Busy, Summer Solstice, Xiaoshu, Dashu, beginning of autumn, Chushu, Bailu, Equinox, Cold Dew, First Frost, beginning of winter, Light Snow, Heavy Snow, Slight Cold and Severe Cold.

On March 20-22 of the vernal equinox (usually at 3-2 1), the straight equator is as long as day and night; The intersection of summer solstice June 2 1-22 (6-2 1) goes directly to the Tropic of Cancer (northern hemisphere); On September 23rd to 24th of the autumnal equinox, the intersection point (9th to 23rd) is equal to the equator day and night; Winter solstice 65438+February 2 1-23( 12-22) Tropic of Capricorn (northern hemisphere) has short days and long nights.

Depending on the sun starting from vernal equinox (longitude zero, at this moment, the sun shines vertically on the equator), every advance of 15 degrees is a solar term; A week after the operation, I returned to the vernal equinox, which is a tropical year, and the tropical year is 360 degrees, so it is divided into 24 solar terms.

When the sun shines directly on the tropic of Capricorn, this day is called the winter solstice, that is, 65438+February 22. In the northern hemisphere, the days are short and the nights are long, and the phenomenon of extreme night appears in the Arctic Circle. When the sun shines directly on the Tropic of Cancer, this day is called the summer solstice, that is, June 22nd. The days in the northern hemisphere are long and the nights are short, and the Arctic Circle has extreme days. When the sun directly hits the equator for the first time, this day is called the vernal equinox, that is, March 2 1 day, and the world is divided into day and night on average; The second direct event on the equator is the autumnal equinox, that is, September 23, when the world distributes day and night equally.