1. Dog Day begins on the third Geng Day after the summer solstice.

2. The dog days are divided into the first, middle and last days. One dog day lasts for 30 or 40 days. Not only is the number of days of Futian uncertain, but the date when the number of Futian begins varies every year.

3. To accurately count the days of dog days, you need to understand the summer solstice and the method of counting days with stems and branches. In fact, the starting date of Shufu does not start from a fixed date in the Gregorian calendar or the lunar calendar, but is calculated through the zodiac calendar method.

4. The summer solstice is the 10th solar term among the twenty-four solar terms, and the time is between June 21st and 22nd in the Gregorian calendar every year. On this day, the sun shines directly on the Tropic of Cancer, making it the longest day of the year in the Northern Hemisphere. Shortly after the summer solstice, it is the dog days.

5. As the saying goes: "At the summer solstice, the number of volts is the number of volts." The word "geng" refers to the geng in the heavenly stems. This sentence means that the third Geng day after the summer solstice is the first day of Chufu.