When the earth's revolution approaches the perihelion, it is at the beginning of July every year, and the closest solar term to the earth is the summer solstice, that is, June 22, so the closest solar term to the earth on June 22 is the summer solstice.

Twenty-four solar terms are an auxiliary calendar formulated in the pre-Qin period and completely established in the Han dynasty, which is used to guide farming. By observing the annual movement of the sun, we can know the changing laws of the four seasons, climate and phenology in a year.