The meaning of vernal equinox, autumnal equinox, summer solstice and winter solstice

1, vernal equinox, summer solstice, autumn equinox and winter solstice are determined by the height of the sun. Solstices in summer and winter are the days when the sun's orbit is at both ends. The summer solstice is "the day when the sun reaches the northernmost point" and the winter solstice is "the day when the sun reaches the southernmost point". In contrast, the vernal equinox and the autumnal equinox "just divide the solar height of summer solstice and winter solstice into two equal days". The vernal equinox and autumnal equinox are similar to the summer solstice and the winter solstice, but they are not the same.

2. The vernal equinox is the midpoint, midpoint and midpoint of 90 days in spring. On the vernal equinox, the sun shines almost directly on the equator of the earth, and the whole world is almost as long as day and night. After the vernal equinox, the direct point of the sun began to enter the northern hemisphere, and the days became longer and the nights became shorter in all parts of the northern hemisphere.

The solstice of summer is the arrival of hot summer. The solstice of winter has come, and so has it. Like the winter solstice, the summer solstice is also a solar term reflecting the changes of the four seasons. Astronomy stipulates that the summer solstice is the beginning of summer in the northern hemisphere. From summer to the future, although the direct point of the sun began to move south from the Tropic of Cancer, the daytime in the northern hemisphere began to shorten gradually, and the height of the sun began to decrease day by day for the Tropic of Cancer and its northern area.

Extended data:

The twenty-four solar terms are divided according to the position of the earth on the ecliptic (that is, the earth's orbit around the sun). Depending on the sun starting from the vernal equinox (longitude zero, at this moment the sun shines vertically on the equator), every advance of 15 degrees is a solar term; After a week's operation, I returned to the vernal equinox, which is a tropical year with 360 degrees, so it is divided into 24 solar terms.

12 solar terms, including beginning of spring, Jingzhe, Qingming, Changxia, Mangzhong, Xiaoshu, beginning of autumn, Bailu, Hanlu, beginning of winter, heavy snow and slight cold; The second solar term of each month is "Zhongqi", that is, there are 12 solar terms such as rain, vernal equinox, Grain Rain, Xiaoman, summer solstice, summer heat, summer heat, autumn equinox, first frost, light snow, winter solstice and great cold. "Solar term" and "neutral qi" appear alternately, each lasting 15 days. Now people have collectively referred to "solar terms" and "neutral gas" as "solar terms", that is, 24 solar terms.

Baidu encyclopedia, 24 solar terms