The dog days of summer 三伏 (sān fú) fall between Slight Heat and Great Heat. They are humid and sultry days with the highest temperatures of the year. “伏(fú)” means the weather is so hot that it is advisable to lie down than to move. The dog days, consisting of the first, the second and the third period of the hot season, refer to the thirty to forty hottest days of the year. The dog days are determined according to the Chinese lunar calendar and they usually fall between mid July and early August.