What is the coldest day and the coldest month in early winter?

During the winter solstice and the light snow festival (equivalent to October of the lunar calendar), there is often a warm weather like spring, so that some fruit trees mistakenly think that spring has come and bloom for the second time. As the saying goes, "August is warm, September is warm, and October is sunny."

In the dead of winter, the so-called "March 9 cold" is usually when it is not too cold before the winter solstice. Starting from the winter solstice, every nine days counts as a "nine", the first nine days are called "one nine", the last nine days are called "two nine", and so on. The coldest period of the year is "three nine days".

Astronomical variation of extended data

At first, bucket handle's direction decided the alternation of seasons, and the Big Dipper rotated in cycles, which was closely related to the change of seasons. Taking the direction pointed by Beidou bucket handle as the standard to judge the season is called sword fighting, and when Beidou bucket handle points to the northwest, it is called beginning of winter solar term.

The current "twenty-four solar terms" come from the "Dayang Huangjing Longitude Method" concluded more than 300 years ago (used since 1645), and the "Dayang Huangjing Method" is a method to determine solar terms according to the position of the sun on the ecliptic.

That is to say, on a 360-degree circle "ecliptic" (the apparent path of the sun on the celestial sphere for one year), it is divided into 24 equal parts, each equal part is 15, with spring as the starting point of 0 degrees (but beginning of spring is still ranked first in the ranking), and it is arranged in longitude.