Why does it always fall on July 7th?

The time of light summer is different from year to year. Every year around July 6 -8 of the Gregorian calendar, when the sun reaches the yellow meridian 105, it is regarded as a light summer solar term.

"Twenty-four solar terms": "June Festival" ... It is also hot in summer, and it is small at the beginning of the month, big in the month, and still small today. "Summer heat. The ancients thought that the summer heat period was not the hottest time of the year, so it was called summer heat.

There is also a solar term ballad: "Little summer is not hot, big summer is three days." It is pointed out that the hottest period of the year has arrived, but it has not reached the extreme hot level. As the saying goes, "the heat is at three volts." The dog days in China generally appear in the summer to the next 28 days, which is the so-called "summer solstice is the first of the night"

In ancient China, the summer heat was divided into three periods: "First, it was warm and windy; Second, wait for crickets to live in space; The third waiting eagle began to crow. " In summer, there is no cool wind on the earth, and all the winds carry heat waves; The Book of Songs? In July, the words to describe crickets are "July is in the wild, August is in the house, September is in the house, and October crickets enter my bed."