How to calculate the ambush of Sangeng on the summer solstice?

This is one of the ways to calculate the dog days in China lunar calendar, that is to say, from the solstice in summer, the third Geng Day will enter the dog days.

Heavenly stems and earthly branches recorded the time in ancient times, and the word "Geng" in the three gengzi was the seventh word in the ten-day trunk of the numbers "A, B, C, D, E, Ji, G, Xin, Ren and Gui", which was repeated every 10 day on Geng Day. I was three years old on the solstice of summer and my head fell off. Astronomical experts said that although the summer solstice indicates that the hot summer has arrived, it is not the hottest time, because the heat near the ground is still accumulating and has not reached its peak. From mid-July to mid-August, the temperature is the highest in all parts of the country.

How to calculate the autumn of Xia San Geng?

The summer solstice begins on "Summer Day" and the third "Geng Day". The fourth to fifth tables are middle tables, and the first to second tables after beginning of autumn are final tables, which are called "three volts". The dog days are the hottest period of the year, because the nights are getting shorter and shorter, the days are getting longer and longer, and the sunshine is close to direct sunlight.