What does midsummer mean?

In midsummer, people often say that it is hot in the dog days. "V" means to hide for the summer. The dog days reflect the general situation of China's midsummer changes and contain many scientific truths. It is closely related to agricultural production and our daily life. The date of the dog days is determined by the date of the trunk and branches. The third watch day from summer solstice is the first day, the fourth watch day is the middle day, and the first watch day from autumn is the last day, which is collectively called the third day. "Geng" is the "Geng" in decameron. The gengxu interval is 10 days, while the solar calendar is 365 days a year (one more day in leap year), not an integer multiple of 10. So the date of Geng Day is different every year, so the date of its first appearance is also different. But the first onset date must be in early July, and there are some other laws: when the first onset date of two consecutive years is a flat year or the first year is a leap year, and the second year is a flat year, the first onset date of the next year is 5 days earlier or later than the previous year; When the first year is a flat year and the second year is a leap year, the first day of the next year is 6 days earlier or 4 days later than the previous year. For example, the initial date of 1990 is July 14, 199 1 9, 1992 is July 13,13. The time from initial lodging to intermediate lodging is fixed at 10 day. The time from the middle period of lodging to the end of lodging is not fixed, because the date of lodging is the first Geng Day after beginning of autumn. When there are 4 shifts before the arrival of beginning of autumn, the time from the middle lodging stage to the end lodging stage is 10 days. When there are five Geng days before beginning of autumn arrives, the interval from mid-lying to last lying is 20 days.

The dog days usually appear after the intense heat in beginning of autumn, that is, from mid-July to mid-August in the solar calendar. The temperature is the highest and the weather is the hottest in dog days. According to the statistics of national average temperature data for many years, Beijing and Changchun have the highest temperatures in mid-July, Nanjing and Hankou have the highest temperatures in late July, Nanchang and Changsha have the highest temperatures in early August, and Guangzhou has the highest temperatures in mid-August, almost all in dog days.

The dog days are the hottest, because the ground heat is accumulated step by step, but the temperature is rising step by step. In most parts of the northern hemisphere, the days are the longest and the sunshine is the strongest in summer solstice. At first glance, the summer of solstice seems to be the hottest day, but it is not the case. Because after the summer solstice, for a long time, the days are still long, the nights are also long, the sunshine is still strong, the heat income on the ground is still greater than the expenditure, and the ground continues to gather heat and heat up. It was not until one month after the summer solstice that the heat accumulated on the ground reached its peak. Coupled with the influence of the Pacific subtropical warm and high pressure, the weather is the hottest, and it is also a dog day.