What is the dog days in summer?

The date of stay varies from year to year. It starts from summer to the first Geng day in the future and ends on the day before the second Geng day after the beginning of autumn, and generally appears in the solar calendar from mid-July to mid-August.

In the calendar, the dog days do not start from a fixed date, but have a set of calculation modes. The date of dive can be expressed by the formula of "three gengzi" from summer to day, that is, from summer to the third gengzi in the future.

It was initially set as 10 day, and finally set as 10 day, while some years in the middle section were 10 day and some years were 20 days. The determination method is as follows: if there are 4 Geng days between the summer solstice and the beginning of autumn, the middle part is 10 days; If there are five more days between the summer solstice and the beginning of autumn, the middle part is 20 days.

Add up the first, middle and last three days and you can get the total number of days in dog days. In other words, there are 30 days in dog days and 40 days in dog days.