Why is there a saying about the winter solstice solar terms?

This is because there is a "winter solstice" in the earth's orbit. The earth moves to the winter solstice, which is the moment of winter solstice. Astronomy can be accurate to microsecond level. The winter solstice is the perihelion, when the angular velocity and linear velocity of the earth are the largest.

On the contrary, in summer solstice, the earth is at apohelion, and its angular velocity and linear velocity are the smallest.

In fact, China knew the existence of "winter solstice" in ancient times. In Qionglin, a kindergarten student, it is said that "autumn begins to leave the tung tree, but winter solstice leaves ashes". Jia ash is the ash burned by reed film. On the day of winter solstice, put "pepper" on the ground. At the moment of winter solstice, pepper will fly, indicating that the "Yang Qi" of "winter solstice is the sun" blows pepper up. I haven't tried, but I don't believe it.