The "dog days" are from the summer solstice (June 2 1 day or 22 in the solar calendar), the third Geng day is the first (with ten days), the fourth Geng day is the middle (with ten days in some years and twenty days in others), and the first Geng day after beginning of autumn (August 7 or 8 in the solar calendar) is the dog days with ten days. In this way, there will be a fixed date for the dog. According to this regulation, it can be calculated that the dog days are from mid-July to mid-August in the solar calendar.

third nine-day period after the winter solstice—coldest days of winter

"Sanjiu" refers to the third "nine days" after the winter solstice, that is, the 19th to 27th days after the winter solstice. There is a saying of "Jiujiu" in Chinese lunar calendar, which is used to calculate the seasons. The calculation method is to count from the winter solstice in winter (starting from the winter solstice, it means the beginning of cold), and every nine days are called a nine, the first nine days are called a nine, the second nine days are called a two-nine, and so on, until the ninth nine days, when the number reaches 9981 days. At this time, winter has passed and spring has arrived.

Generally, it is the coldest in the "March 9th".