Why does the heat have 30 days and 40 days?

The first and last days are 65,438+00 days, and the middle days are not fixed. This is because when there are four more days between the summer solstice and the beginning of autumn, the middle is 65,438+00 days, and when there are five more days, the middle is 20 days.

So the period from "mid-range" to "terminal" is sometimes 10 days, and sometimes it is 20 days. This has caused some years to have 30 days in dog days, some years to have more 10 days because of dog days, and the dog days add up to 40 days.

Autumn belongs to "Geng Xin Gold", so "ambush" should start from "Geng Day". The temperature is the highest, and it needs to be hidden for 20 days from summer to the future, so it starts from summer to the third "watch" in the future and ends on the second watch after beginning of autumn.

If Geng Day falls on beginning of autumn Day and two days later, the sum of summer days is 30 days, otherwise the sum of summer days is 40 days. Summer is between summer and midsummer, and it is the hottest, humid and sultry day of the year.

"Fu" means that the weather is too hot to move. Xiafu is the hottest 30-40 days in a year in the Central Plains. According to the lunar calendar, it is from mid-July to early August in the solar calendar.