What does it mean to get hot on the midsummer solstice?

This sentence is about how people calculate the time of falling into the sky every year. The summer solstice is one of the 24 solar terms of the lunar calendar, and the time is around June 2 1 of the Gregorian calendar every year. The summer heat began on the third Geng day after the summer solstice solar terms. Summer lodging is "three volts", which is the hottest thirty or forty days in a year, and it is divided into initial lodging, middle lodging and final lodging. "Night till the sun" is the first day of early autumn.

According to the calculation rules in dog days, the third Geng day from summer to the future is the beginning of the first squat, the fourth Geng day is the beginning of the middle squat, and the first Geng day after beginning of autumn is the beginning of the last squat. The first and last days of each year are 10 days, and some years are 10 days, and some years are 20 days.

There are 45 days between the summer solstice and the solar terms in beginning of autumn. If there are four Geng days in this period, there are 10 days in the middle, and if there are five Geng days in this period, there are 20 days in the middle.