What time is used to calculate the first day?

The extinction date of the twenty-four solar terms can be calculated by the formula of "the third night of the summer solstice" Starting from the summer solstice, according to the date of trunk, the third Geng day is the first, the fourth Geng day is the middle, and the 1 th Geng day after beginning of autumn is the last. The interval of each Geng day is 10 day, the time from initial lodging to intermediate lodging is 10 day, and the final lodging is 10 day. The midsummer may be 10 day or 20 days: when there are four Geng days between the summer solstice and the beginning of autumn, the midsummer is 10 day, and when there are five Geng days, it is 20 days.

June 2 1 this year is the summer solstice, which is Bingzi Day, followed by Chen Geng Day on June 25, Gengyin Day on July 5, and Gengzi Day on July 15. The third boxer day from summer to the future is the boxer day on July 15, and it begins to fall. July 25th is the first day of Zhongfu, and there are five more days from the solstice in summer to this year's beginning of autumn. Therefore, the medium dose lasts for 20 days. August 7th this year in beginning of autumn, August 14 is the first day of the last autumn. As the saying goes, there is no end to autumn, and there is autumn after autumn.

The "Geng Day" mentioned here refers to the day prefixed with Geng according to the "heavenly stems and earthly branches auspicious day law". Among them, Tiangan consists of 10, which are a, b, c, d, e, f, g, Xin, n and d in turn. The earthly branches are composed of 12, which are Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai in turn. Each "stem" and each "stem" are arranged in sequence as the names of each day, such as "Jiazi Day" and "Gengwu Day" ... so that the two "Gengri Days" are just 10 days apart. "One volt" and "three volts" are both 10 days, while "two volts" are sometimes 10 days and sometimes 20 days.