What does the lunar calendar mean?

In the calendar, Sanjiu means the third nine days from winter to the future, that is, the nineteenth day to the twenty-seventh day of the winter solstice in the lunar calendar.

Sanjiu is in the middle of the number nine, and the weather is coldest. There is a passage in the well-known "99 Songs": "1929 does not shoot, but walks on the ice in 3949. In 5969, I watched willows along the river. Seventy-nine rivers opened, eighty-nine geese came, ninety-nine and nineteen, and I plowed cattle everywhere. " Among them, Walking on the Ice in March 1949 said that March 1999 and April 1999 were the coldest seasons of the year, and there was thick solid ice in the river, so pedestrians could walk safely on the river.

The number nine method is passed down from mouth to mouth in some places in China, which has a history and lacks records. As for when it originated, there is no exact information. The ancients followed the example of the sky, took the image of the land, set solar terms to know solar terms, and made calendars to know time changes; Qi is divided into yin and yang, everything flows, man and astronomy are interlinked, and Tao becomes nature. In our traditional philosophy, yang grows and yin disappears, symbolizing cold and warm.

Introduction of coldest time in March and September

During the winter solstice, the daytime is the shortest, the angle of direct sunlight on the ground is the smallest, and the sunshine intensity per unit area on the ground is also the smallest, so the ground gets the least solar heat every day, and the daily heat budget deficit on the ground has not reached the maximum. On the solstice after winter, although the day is growing day by day, the growth rate is very slow. From the winter solstice to the "March 9" period, the average daily growth is only about one minute. At the same time, the angle between the direct angle of the sun and the ground is slowly increasing.

The daily heat budget of the ground is still in deficit, so it continues to lose heat and the ground temperature continues to drop. The deficit of total heat balance on the ground only reaches the maximum in the season of March 9. Because the temperature is mainly affected by the ground temperature, it leads to the lowest temperature in March 9 (of course, this is not the case all over the country, but every year, depending on the region and age). In addition, around March 9, the cold air mass in Siberia also developed to a strong stage.