The first half of the year is June 21, and the second half is August 23. The dates of the two festivals are set every month, with a maximum difference of one or two days.
Since five thousand years of history, China's main political, economic, cultural and agricultural activity centers have been concentrated in the Yellow River Basin [1] Central Plains, and the 24 solar terms have been established on the basis of the climate and phenology in this area. Because of China's vast territory and changeable terrain, the 24 solar terms are only a reference for many regions. As far back as the Spring and Autumn Period, four solar terms, namely, mid-spring, mid-summer, mid-autumn and mid-winter, were set. After continuous improvement and perfection, by the Qin and Han Dynasties, the 24 solar terms had been completely established. In BC 104, taichu calendar, written by Deng Ping, officially set the 24 solar terms in the calendar, and defined the astronomical position of the 24 solar terms. In ancient times, a year was divided into twelve months, and each month had two solar terms. The former is the festival calendar, and the latter is the Chinese spirit. For example, beginning of spring is the first month festival and the rain is in the first month. Later generations refer to the festival calendar and the Chinese spirit as solar terms. The 24 solar terms are divided according to the position of the sun on the ecliptic (that is, the orbit of the earth around the sun). Depending on the sun starting from vernal equinox (longitude zero, at this moment the sun shines vertically on the equator), every forward 15 degrees is a solar term; After a week's operation, I returned to vernal equinox, which is a tropical year, which is 360 degrees, so it is divided into 24 solar terms. The dates of solar terms are relatively fixed in the solar calendar. For example, beginning of spring is always between February 3rd and 5th in the solar calendar. However, in the lunar calendar, the date of the solar term is not easy to determine. Take beginning of spring as an example, it can be on1February 15 of the previous year's lunar calendar and on 15 of the first month at the latest. The current lunar calendar is neither a lunar calendar nor a solar calendar, but a combination of lunar and solar calendars. There are leap months in the lunar calendar. If one year is counted from the first day of the first month to the New Year's Eve of the twelfth month, the number of days in each year of the lunar calendar varies greatly (leap year 13 months). In order to standardize the number of years, the first day of the lunar calendar year (heavenly stems and earthly branches) is not the first day of the first month, but beginning of spring. That is, a year in the lunar calendar is the day before from beginning of spring in that year to beginning of spring in the following year. For example, 2008 is the year of Wuzi, and the first day of Wuzi is not February 7, 2008 (the first day of the first lunar month), but February 5, 2008.