Today's yellow calendar

The twenty-four solar terms are based on the astronomical calendar, which was formulated by the ancients according to the astronomical phenomena and combined with the guidance of farming. A solar term is about 15 days, and a solar term is divided into three parts. A cycle is exactly 5 days, and 24×3=72 has 72 cycles a year. "Wait for 73 days" and "Wait for 5 days" are both general terms, which are aimed at ordinary people or people who don't understand astronomical calendars.

The ancient calendar in China is mainly a combination of two calendars, namely the solar calendar and the lunar calendar. The ancient solar calendar is not the universal Gregorian calendar in the world today. The solar calendar used by our ancestors is mainly a dry calendar, which needs to be made by constantly measuring astronomical phenomena, synchronized with astronomy and complicated. Because of the earth's revolution speed, precession and sidereal years, the sun looks neither uniform nor equal on the ecliptic.

Due to these complex changes in the sky, the solar term time is different every month. In each dynasty, Qin Tianjian devoted himself to observing astronomical measurements, calculating accurate solar terms and making calendars. Therefore, "some solar terms in the current yellow calendar are only 14 days or 16 days", which was formulated by Zijin or the National Astronomical Observatory through observational astronomy.

The ancients thought that there were five degrees in the sky, and after five degrees, the numbers changed. The climate corresponds to the fifth degree of the ecliptic, which is consistent with the astronomical phenomena in the calendar. The ancients thought that farming should correspond to the weather, and the four seasons, six atmospheres and three climates all depended on the astronomical phenomena, so the so-called general reference was not accurate.

Another solar term has nothing to do with the size of the moon, but only with the solar calendar or the speed of the earth's orbit. Big month and small month are concepts in lunar calendar and Gregorian calendar. They are different calendars.