72 yellow calendar

Twenty-four solar terms were formulated by the ancients according to the astronomical calendar and the guidance of agriculture. A solar term is about 15 days, and a solar term is divided into three points. 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 all general statements, aiming 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 surveying the astronomical phenomena, which is synchronous 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.

Because of these complicated changes in the sky, the preservation time of solar terms is different every month. In each dynasty, Qin Tianjian devoted himself to observing astronomical measurements, calculating accurate solar terms and drawing up 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 by observing astronomy.

The ancients thought that there were five degrees in the sky, five degrees, and after five degrees, the number 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 qi and three qi all depended on the astronomical phenomena, so the so-called general reference was not accurate.

The other solar term has nothing to do with the size of the moon, but only with the solar calendar or the revolution speed of the earth. Big and small months are concepts in the lunar calendar and the Gregorian calendar, which are different calendars.