Ancient books say that the Japanese papermaking sun runs to the northernmost day, and from that day on it enters the hot season. What festival is this?

Solar term is a special festival in the trunk and branch calendar that expresses the change of natural rhythm and establishes "December construction" (monthly order). The 24 solar terms are: beginning of spring, Rain, Sting, Equinox, Qingming, Grain Rain, Changxia, Xiaoman, Mangzhong, Summer Solstice, Xiaoxia, Daxia, beginning of autumn, Early Summer, Bailu, Autumn Equinox, Cold Dew, Early Frost, beginning of winter, Light Snow, Heavy Snow, Winter Solstice, Slight Cold and Severe Cold. The twenty-four solar terms are related to cadres and gossip and have a long history. In the historical development, the 24 solar terms have been incorporated into the lunar calendar and become an important part of the lunar calendar.