Are there any rules in the lunar calendar?

The moon orbits the earth for 29.53 days (30 days in the first lunar month and 29 days in the second lunar month), and the earth orbits the sun for 365.25 days. In this way, the moon has to make 12.37 revolutions every year to synchronize with the revolution between the earth and the sun. This is why the lunar calendar leaps for one month every three years or so. (Usually 19 7 leap) Which leap? This means that 24 solar terms and 24 solar terms were obtained by ancient astronomers in China who observed the relationship between the earth and the sun, and had nothing to do with the moon. Simply put, the circumference is divided into 24 equal parts with the sun as the center, and each equal part is divided into a solar term. Every solar term is average.

15, 22 days. There are 1.94 solar terms on average in January of the lunar calendar. Less than two. Therefore, according to the lunar calendar, if there is only one solar term in any month, then next month is a leap month. Then you may ask: In that case, which month is not a leap month should be random. Why not watch leap December and leap January? This is because the earth revolves around the sun in an oval shape. In winter in the northern hemisphere, the earth is closer to the sun, and the speed of the earth's orbit around the sun is relatively fast, only about 1.4 days and a half, which happens to be the first month of the lunar calendar with two solar terms. That's why we don't have two twelfth lunar months and two New Year's days in a year. When I started to answer, no one answered. When I finished, I found that I was teaching fish to swim.