Proverbs often say: practice three summers in summer and three days in winter. What exactly are three summers? What are the dog days? ;

It should be: three or nine days in winter and three days in summer.

Three volts (summer) is a solar term. Three volts means that the first day is from summer to the third Geng day in the future, and then it is a volt every ten days. The third ten days in the dog days are the hottest; Judging from the date of winter solstice, there are nine days every nine days, and the third nine days is the coldest March 9th.