What is the "arrival" of the summer solstice?

Drawing: Chen Xiaocheng

June 21 is the summer solstice of this year.

What does the "Zhi" of the summer solstice mean? Does it mean? In fact, the "Zhi" here refers to "extreme, the most", emphasizing the extreme in the astronomical sense. "Extreme", there are two more layers of meaning:

The first layer is the longest of the day of the northern hemisphere. On the day of summer solstice, except for Hainan and other places, most regions in my country are the longest of the year, and the length of the day is greater than the night, and the longer the north day. For example, Harbin sunshine time is about 16 hours, and Nanjing can reach 14 hours, even in Haikou, there are 13 hours.

The second meaning is the largest angle of the solar (that is, the angle between the incident of sunlight and the ground surface of the earth). Nikko is a time instrument that uses the time to measure the moment of the sun. On this summer solstice, the sun shot from the sun in the sun can not form a shadow to indicate the time on the noodles -from the perspective of modern astronomy, the emergence of this phenomenon is because at this time the height angle of the northern hemisphere is the largest, almost direct shooting the north, which almost shines in the north. Return area. In most parts of our country, on the summer solstice, the high angle of the sun has reached the maximum of the year.

In fact, the entire twenty -four solar terms are closely related to the height of the sun. The ancients found that with the movement of the sun, the shadow of the object would also move accordingly. Using the instrument, they also slowly discovered the longest summer solstice of Sun Ying and the longest winter solstice, and determined the length of the return year by measuring the winter solstice of the adjacent two years. Then, the law of the long and short changes of the shadow, combined with the law of the climate of the climate, established the spring equinox, autumnal equinox, Lichun, Lixia, Liqiu, Lidong, etc., and gradually outlined the image of the year and four seasons.

The longest sunshine time and the largest height angle, so is the summer solstice the hottest day of the year? In fact, because the light time is long and the surface solar radiation is sufficient, the temperature will indeed be relatively high during the summer solstice. However, after the summer solstice, because the sunlight will "scan" the northern hemisphere again to the south, the heat will continue to save, and then we will usher in the two hottest solar terms in summer -small summer and heavy summer.

It is worth mentioning that the meteorology gives standards for the temperature of the temperature: the highest temperature of the daily maximum temperature or more than 35 degrees Celsius is called a high temperature, and it is called the hot summer when it reaches or exceeds 37 degrees Celsius.

"The green trees are long and long in the summer, and the platform is pouring into the pond." Although the summer solstice is hot, it is the time when everything grows lush.

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(Source: People's Daily)

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