Please explain in detail how to calculate the third Geng Day "The third Geng Day after long summer is the first day of the solstice".

"Three Geng" is the first time to meet three "Geng" characters, and the third Geng Day is the first time. Because there are 10 days, there is a Geng Day every 10 day, such as Geng Zi Day, Geng Yin Day and Chen Geng Day.

Dog days, one volt is ten days, counted by days. Therefore, the dog days are divided into three days, that is to say, after the third day of Gengtian, the summer solstice is the first day, the first volt. For example, the summer solstice in 2006 is June 2 1 in the western calendar year. The dry day of this day is Xin Day, and 28 days later is the third Geng Day.

Therefore, July 20, 2006 is the second dry day, and it entered the second volt on July 29; Ten days later, it was another Geng day, that is, August 9, and it entered the dog days. In other words, it is very hot after entering the dog days every year, especially on the tenth day of dog days, which is the hottest.