Solar terms play with numbers in Song Dynasty.

The "several volts" of the solar term Song began on the first Geng day after the summer.

The "number nine" of the solar term Song began on the day of winter, which is generally 65438+February, 2 1 or 22 days every year.

How many volts are there in three volts? "Three volts" refers to the initial, middle and final three volts, probably from mid-July to mid-August. After the summer solstice, although the days are getting shorter and the nights are getting longer, the days are longer than the nights in a day. Every day, the ground absorbs more heat than it emits, and the temperature near the ground is getting higher every day.

During the "three volts" period, the heat absorbed by the ground is almost less than the heat emitted, and the weather is the hottest.

On the solstice after beginning of winter, "counting nine", commonly known as "crossing nine", means entering the coldest season of the year. The so-called "number nine" means that from the date of the "winter solstice", nine days is a unit, which is called "nine". After nine "nines", it is exactly 8 1 day, which is called "nine". From "September 19th" to "September 9th", the cold winter turned into a warm spring. Among them, March 9 is the coldest.