The solstice summer is getting shorter and shorter, isn't it? Or does it start to get shorter after 18 days from the summer solstice?

After the summer solstice, the days begin to shorten. From summer to the sun, the direct position of the sun on the ground reaches the northernmost point of the year, almost directly to the Tropic of Cancer, with the shortest sun shadow, the longest day and the shortest night in the northern hemisphere.

The solstice in summer is also the turning point of the sun. The point of direct sunlight moves southward from the tropic of cancer, and the days in the northern hemisphere will get shorter day by day. For the Tropic of Cancer (23 26' north latitude) and its northern area, after the summer solstice, the noon sun height began to decrease day by day.

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The origin of summer solstice

Among the 24 solar terms, the solstice in summer and the solstice in winter are the earliest two solar terms determined by the ancients. The vernal equinox, autumnal equinox and "four solar terms" (beginning of spring, long summer, beginning of autumn and beginning of winter) are all determined on the basis of "two solstices".

According to "Yao Dian of Shangshu", in order to calculate the age, Emperor Yao made a calendar and ordered his uncle Xi to go to a place called Du Ming in the south to observe the changes caused by the sun moving from north to south. As a result, he found that "the sun always has sparks." That is to say, when the fire lodge in the Seven Nights of the Oriental Black Dragon appears in the southern sky, this day is the longest, so it is determined that this day is the summer solstice of the second month of summer.

Baidu encyclopedia-summer solstice