To enter the ambush means to enter the dog days. "Fu" is a popular saying among the people, which means that Yin qi is oppressed by Yang qi and hides in a low position. After falling, it means entering the hottest time of the year.
The determination of the lodging time in China is based on the ancient popular "trunk and branch calendar method", and 60 groups of different names matched with 10 heavenly stems and 12 earthly branches are used to record the days and recycle them.
The whole dog days will last for about 40 days, divided into three stages: initial, intermediate and final. After three Geng days of the summer solstice, counting to the fourth Geng day is the initial stage, the fourth Geng day to the fifth Geng day is the intermediate stage, and the first Geng day to the second Geng day after beginning of autumn is the final stage. Every Geng day is 10 days apart, and the number of midsummer days is not fixed. There are four Geng days between the summer solstice and beginning of autumn, the midsummer days are 10 days, and when there are six Geng days, the midsummer days are 20 days.
Although the dog days are the hottest period of the year, there is still a certain temperature difference in the three stages of the dog days. In the dog days, the nights are short and the days are long. The direct sunlight lasts for a long time, so the heat absorbed by the surface will be far greater than the heat emitted, and a large amount of heat will accumulate on the surface of the ground, making the temperature at the end of the day slightly higher than that at the beginning.