What are the unusual full moon months in China?

May, June and July are the most common months, and there are other months, but there are almost no first and twelfth months. At present, the lunar calendar uses fixed new moon and fixed sky to arrange the moon and the sun, and the time of fixed new moon and fixed sky is calculated according to the precise orbit.

The orbit of the earth's revolution is elliptical, so the speed of the earth is fast and slow. The speed is the fastest at perihelion, so the angle swept by revolution is the fastest. However, solar terms (corresponding to a latitude circle where the sun shines directly on the ground) are closely related to the angle swept by the earth's revolution. The faster the angle swept by the earth's revolution, the shorter the time it takes to pass through each solar point in the orbit. On the contrary, the slower the angle swept by the earth's revolution, the longer the time interval through each solar point in the orbit. Therefore, the time interval of solar terms near the perihelion (about 13 days from winter to the future) may be shorter than the time interval between two fixed days (the number of days in a lunar month), so it is very unlikely that the lunar month near the perihelion is not neutral. Both 65438+February and the first lunar month are near the perihelion, so the probability of becoming a leap month will be even smaller.

On the contrary, the time interval of solar terms near the perihelion (about 13 days from summer to the future) may be longer than the time interval between two fixed days (the number of days in a lunar month), so there are many opportunities for May, June and July of the lunar calendar to be neutral near the perihelion, so the lunar calendar will leap May, June and July. However, since the Qing Dynasty 1645, leap January and leap February 12 have never appeared once.

In fact, perihelion is the "leap decline" point of the lunar calendar, and apohelion is the "leap surplus" point of the lunar calendar. At present, the frequency of leap month reflects the astronomical phenomenon of the changes of perihelion and apohelion of the earth, and leap month is also of great astronomical significance. Due to the influence of the celestial pole shift, the long axis of the earth's orbit is slowly moving eastward relative to a certain point on the ecliptic, and the vernal equinox is slowly moving westward relative to a certain point on the ecliptic, so the perihelion is moving away from the winter solstice and towards the vernal equinox. In the future, when the perihelion moves to the summer solstice, it will be the opposite of the current situation, that is, leap May and June are not easy to happen, but leap 65438+ February and leap first month are very common.