Why doesn't the lunar calendar decorate the first month and the twelfth month?

Lunar calendar adopts fixed new moon, fixed sky, moon and 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's rotation is fast or slow. The perihelion is the fastest, so the revolution angle is the fastest. Solar terms (a latitude circle corresponding to the direct sunlight on the ground) are closely related to the revolution angle of the earth. The greater the angle of the earth's revolution, the faster it will pass through the solar terms in 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, while the vernal equinox is slowly moving westward relative to a certain point on the ecliptic, and the perihelion is moving away from the winter solstice and towards 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 12 and leap January are very common. At that time, we will celebrate Lunar New Year's Eve and Spring Festival at the end of leap 65438+February, while Laba Festival (65438+February 8) and off-year (65438+February 23) are celebrated, that is, Laba Festival (simple Laba Festival, the eighth day of the twelfth lunar month, it is no longer the exact day of the New Year. This day will be leap 65438+February 8) and the second Laba Festival (lunar leap 65438+February 8). This day is not only the repetition of Laba Festival, but also the beginning and preparation of the New Year. This is because the Lunar New Year can only be on the first day of the first lunar month, and the first day of leap 65438+ February is not the Lunar New Year, so it is the day before. ), off-year (65438+ February 23rd of the lunar calendar, we will celebrate off-year, and carry out some folk activities other than offering sacrifices to stoves, but the sacrifices to stoves must be held on February 23rd of leap 65438+February 23rd) and the second off-year (that is, leap 65438+February 23rd, the same as previous off-year, and the sacrifices to stoves are also held on this day.