1. The first day of the ambush in 2021 is July 11, and the first ambush is from July 11, 2021 to July 20, 2021, ***10 days.

2. Entering the ambush means entering the dog days of summer. "Summer solstice three Geng several heads fall", this is the basis for establishing the ambush.

3. The Dog Days appear in the period of Xiaoshu and Beginning of Autumn. They are the hottest, humid and sultry days of the year. The so-called "Dog Days" refers to the "Dog Days" of the lunar calendar, which is the hottest period of the year. But the reason why the dog days of summer are called "dog days" is because there are also many cold factors involved. Sanfu is the hottest three to forty days of the year in the Central Plains. Sanfu is calculated according to the lunar calendar, and it is approximately from mid-to-late July to early August in the solar calendar.