1. Chufu: July 11, 2021 - July 20, 2021, ***10 days.

2. In 2021, the ambush will occur after the summer solstice. The summer solstice is June 21, and July 21 after the thirtieth day will be the first day of the ambush. It is divided into the first, middle and last days. Generally, the period from mid-July to mid-August is the hottest time of the year. The time of the Dog Day is not fixed every year, and the length of the Dog Day is also different.

3. There are currently two opinions on the time of the ambush in 2021, one is that it will enter the ambush on July 21, 2021, and the other is that it will enter the ambush on July 11, 2021. This is related to the algorithm of "summer solstice three Geng", which is the third "geng day" from the summer solstice.

4. Because the summer solstice in 2021 is on June 21, this day is the Gengzi day of the Jiawu lunar calendar. If this day is also counted as a "Gengzi day", then the time of entering ambushes will be It is July 11, 2021. Geng day refers to the day with the word "geng" in the zodiac calendar.