The Moon Period of Revolution

The period of the moon's revolution is between 29 and 30 days, and a month in the lunar calendar is only 29 to 30 days before the new moon appears. 30 days for the big moon and 29 days for the small moon. Unlike the solar calendar, large and small months are not fixed in different years. For example, the day before the Spring Festival is usually called New Year's Eve, but in many years, such as the 2000 lunar calendar1February, there are only 29 days. Since the period of twelve months is about shorter than that of the solar year 1 1 day, in order to keep the lunar year and the solar year relatively stable, a leap month should be added every two or three years. About every nineteen years, seven leap months will be added. The 24 solar terms are determined by the position of the earth in its orbit around the sun. Starting from the annual winter solstice, every 15 degree is a solar term. Therefore, the 24 solar terms have roughly fixed dates in each month of the solar calendar. In ancient times, the twenty-four solar terms guided farming, which is why the lunar calendar is also called the lunar calendar. Among them, the twelve solar terms in the second half of the solar calendar are also called zhongqi. The time when Qi appears is directly related to the determination of leap month.