The dog days are the hottest thirty or forty days in a year in the Central Plains. The dog days are calculated according to the lunar calendar, that is, from the middle and late July to the early August of the solar calendar. The time of accommodation is not fixed every year, and the length of accommodation is also different. You need to check the almanac to calculate it. Simply put, we can use the formula of "Xia San Geng" to express the lodging date, that is, from the third Geng day in Xia Hou, the initial lodging is 10 day, the intermediate lodging is 10 day or 20 days, and the final lodging is 10 day.